1IO::Socket::SSL(3)    User Contributed Perl Documentation   IO::Socket::SSL(3)
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NAME

6       IO::Socket::SSL - SSL sockets with IO::Socket interface
7

SYNOPSIS

9           use strict;
10           use IO::Socket::SSL;
11
12           # simple client
13           my $cl = IO::Socket::SSL->new('www.google.com:443');
14           print $cl "GET / HTTP/1.0\r\n\r\n";
15           print <$cl>;
16
17           # simple server
18           my $srv = IO::Socket::SSL->new(
19               LocalAddr => '0.0.0.0:1234',
20               Listen => 10,
21               SSL_cert_file => 'server-cert.pem',
22               SSL_key_file => 'server-key.pem',
23           );
24           $srv->accept;
25

DESCRIPTION

27       IO::Socket::SSL makes using SSL/TLS much easier by wrapping the
28       necessary functionality into the familiar IO::Socket interface and
29       providing secure defaults whenever possible.  This way, existing
30       applications can be made SSL-aware without much effort, at least if you
31       do blocking I/O and don't use select or poll.
32
33       But, under the hood, SSL is a complex beast.  So there are lots of
34       methods to make it do what you need if the default behavior is not
35       adequate.  Because it is easy to inadvertently introduce critical
36       security bugs or just hard to debug problems, I would recommend
37       studying the following documentation carefully.
38
39       The documentation consists of the following parts:
40
41       ·   "Essential Information About SSL/TLS"
42
43       ·   "Basic SSL Client"
44
45       ·   "Basic SSL Server"
46
47       ·   "Common Usage Errors"
48
49       ·   "Common Problems with SSL"
50
51       ·   "Using Non-Blocking Sockets"
52
53       ·   "Advanced Usage"
54
55       ·   "Integration Into Own Modules"
56
57       ·   "Description Of Methods"
58
59       Additional documentation can be found in
60
61       ·   IO::Socket::SSL::Intercept - Doing Man-In-The-Middle with SSL
62
63       ·   IO::Socket::SSL::Utils - Useful functions for certificates etc
64

Essential Information About SSL/TLS

66       SSL (Secure Socket Layer) or its successor TLS (Transport Layer
67       Security) are protocols to facilitate end-to-end security. These
68       protocols are used when accessing web sites (https), delivering or
69       retrieving email, and in lots of other use cases.  In the following
70       documentation we will refer to both SSL and TLS as simply 'SSL'.
71
72       SSL enables end-to-end security by providing two essential functions:
73
74       Encryption
75           This part encrypts the data for transit between the communicating
76           parties, so that nobody in between can read them. It also provides
77           tamper resistance so that nobody in between can manipulate the
78           data.
79
80       Identification
81           This part makes sure that you talk to the right peer.  If the
82           identification is done incorrectly it is easy to mount man-in-the-
83           middle attacks, e.g. if Alice wants to talk to Bob it would be
84           possible for Mallory to put itself in the middle, so that Alice
85           talks to Mallory and Mallory to Bob.  All the data would still be
86           encrypted, but not end-to-end between Alice and Bob, but only
87           between Alice and Mallory and then between Mallory and Bob.  Thus
88           Mallory would be able to read and modify all traffic between Alice
89           and Bob.
90
91       Identification is the part which is the hardest to understand and the
92       easiest to get wrong.
93
94       With SSL, the Identification is usually done with certificates inside a
95       PKI (Public Key Infrastructure).  These Certificates are comparable to
96       an identity card, which contains information about the owner of the
97       card. The card then is somehow signed by the issuer of the card, the CA
98       (Certificate Agency).
99
100       To verify the identity of the peer the following must be done inside
101       SSL:
102
103       ·   Get the certificate from the peer.  If the peer does not present a
104           certificate we cannot verify it.
105
106       ·   Check if we trust the certificate, e.g. make sure it's not a
107           forgery.
108
109           We believe that a certificate is not a fake if we either know the
110           certificate already or if we trust the issuer (the CA) and can
111           verify the issuers signature on the certificate.  In reality there
112           is often a hierarchy of certificate agencies and we only directly
113           trust the root of this hierarchy.  In this case the peer not only
114           sends his own certificate, but also all intermediate certificates.
115           Verification will be done by building a trust path from the trusted
116           root up to the peers certificate and checking in each step if the
117           we can verify the issuer's signature.
118
119           This step often causes problems because the client does not know
120           the necessary trusted root certificates. These are usually stored
121           in a system dependent CA store, but often the browsers have their
122           own CA store.
123
124       ·   Check if the certificate is still valid.  Each certificate has a
125           lifetime and should not be used after that time because it might be
126           compromised or the underlying cryptography got broken in the mean
127           time.
128
129       ·   Check if the subject of the certificate matches the peer.  This is
130           like comparing the picture on the identity card against the person
131           representing the identity card.
132
133           When connecting to a server this is usually done by comparing the
134           hostname used for connecting against the names represented in the
135           certificate.  A certificate might contain multiple names or
136           wildcards, so that it can be used for multiple hosts (e.g.
137           *.example.com and *.example.org).
138
139           Although nobody sane would accept an identity card where the
140           picture does not match the person we see, it is a common
141           implementation error with SSL to omit this check or get it wrong.
142
143       ·   Check if the certificate was revoked by the issuer.  This might be
144           the case if the certificate was compromised somehow and now
145           somebody else might use it to claim the wrong identity.  Such
146           revocations happened a lot after the heartbleed attack.
147
148           For SSL there are two ways to verify a revocation, CRL and OCSP.
149           With CRLs (Certificate Revocation List) the CA provides a list of
150           serial numbers for revoked certificates. The client somehow has to
151           download the list (which can be huge) and keep it up to date.  With
152           OCSP (Online Certificate Status Protocol) the client can check a
153           single certificate directly by asking the issuer.
154
155           Revocation is the hardest part of the verification and none of
156           today's browsers get it fully correct. But, they are still better
157           than most other implementations which don't implement revocation
158           checks or leave the hard parts to the developer.
159
160       When accessing a web site with SSL or delivering mail in a secure way
161       the identity is usually only checked one way, e.g. the client wants to
162       make sure it talks to the right server, but the server usually does not
163       care which client it talks to.  But, sometimes the server wants to
164       identify the client too and will request a certificate from the client
165       which the server must verify in a similar way.
166

Basic SSL Client

168       A basic SSL client is simple:
169
170           my $client = IO::Socket::SSL->new('www.example.com:443')
171               or die "error=$!, ssl_error=$SSL_ERROR";
172
173       This will take the OpenSSL default CA store as the store for the
174       trusted CA.  This usually works on UNIX systems.  If there are no
175       certificates in the store it will try use Mozilla::CA which provides
176       the default CAs of Firefox.
177
178       In the default settings, IO::Socket::SSL will use a safer cipher set
179       and SSL version, do a proper hostname check against the certificate,
180       and use SNI (server name indication) to send the hostname inside the
181       SSL handshake. This is necessary to work with servers which have
182       different certificates behind the same IP address.  It will also check
183       the revocation of the certificate with OCSP, but currently only if the
184       server provides OCSP stapling (for deeper checks see "ocsp_resolver"
185       method).
186
187       Lots of options can be used to change ciphers, SSL version, location of
188       CA and much more. See documentation of methods for details.
189
190       With protocols like SMTP it is necessary to upgrade an existing socket
191       to SSL.  This can be done like this:
192
193           my $client = IO::Socket::INET->new('mx.example.com:25') or die $!;
194           # .. read greeting from server
195           # .. send EHLO and read response
196           # .. send STARTTLS command and read response
197           # .. if response was successful we can upgrade the socket to SSL now:
198           IO::Socket::SSL->start_SSL($client,
199               # explicitly set hostname we should use for SNI
200               SSL_hostname => 'mx.example.com'
201           ) or die $SSL_ERROR;
202
203       A more complete example for a simple HTTP client:
204
205           my $client = IO::Socket::SSL->new(
206               # where to connect
207               PeerHost => "www.example.com",
208               PeerPort => "https",
209
210               # certificate verification - VERIFY_PEER is default
211               SSL_verify_mode => SSL_VERIFY_PEER,
212
213               # location of CA store
214               # need only be given if default store should not be used
215               SSL_ca_path => '/etc/ssl/certs', # typical CA path on Linux
216               SSL_ca_file => '/etc/ssl/cert.pem', # typical CA file on BSD
217
218               # or just use default path on system:
219               IO::Socket::SSL::default_ca(), # either explicitly
220               # or implicitly by not giving SSL_ca_*
221
222               # easy hostname verification
223               # It will use PeerHost as default name a verification
224               # scheme as default, which is safe enough for most purposes.
225               SSL_verifycn_name => 'foo.bar',
226               SSL_verifycn_scheme => 'http',
227
228               # SNI support - defaults to PeerHost
229               SSL_hostname => 'foo.bar',
230
231           ) or die "failed connect or ssl handshake: $!,$SSL_ERROR";
232
233           # send and receive over SSL connection
234           print $client "GET / HTTP/1.0\r\n\r\n";
235           print <$client>;
236
237       And to do revocation checks with OCSP (only available with OpenSSL
238       1.0.0 or higher and Net::SSLeay 1.59 or higher):
239
240           # default will try OCSP stapling and check only leaf certificate
241           my $client = IO::Socket::SSL->new($dst);
242
243           # better yet: require checking of full chain
244           my $client = IO::Socket::SSL->new(
245               PeerAddr => $dst,
246               SSL_ocsp_mode => SSL_OCSP_FULL_CHAIN,
247           );
248
249           # even better: make OCSP errors fatal
250           # (this will probably fail with lots of sites because of bad OCSP setups)
251           # also use common OCSP response cache
252           my $ocsp_cache = IO::Socket::SSL::OCSP_Cache->new;
253           my $client = IO::Socket::SSL->new(
254               PeerAddr => $dst,
255               SSL_ocsp_mode => SSL_OCSP_FULL_CHAIN|SSL_OCSP_FAIL_HARD,
256               SSL_ocsp_cache => $ocsp_cache,
257           );
258
259           # disable OCSP stapling in case server has problems with it
260           my $client = IO::Socket::SSL->new(
261               PeerAddr => $dst,
262               SSL_ocsp_mode => SSL_OCSP_NO_STAPLE,
263           );
264
265           # check any certificates which are not yet checked by OCSP stapling or
266           # where we have already cached results. For your own resolving combine
267           # $ocsp->requests with $ocsp->add_response(uri,response).
268           my $ocsp = $client->ocsp_resolver();
269           my $errors = $ocsp->resolve_blocking();
270           if ($errors) {
271               warn "OCSP verification failed: $errors";
272               close($client);
273           }
274

Basic SSL Server

276       A basic SSL server looks similar to other IO::Socket servers, only that
277       it also contains settings for certificate and key:
278
279           # simple server
280           my $server = IO::Socket::SSL->new(
281               # where to listen
282               LocalAddr => '127.0.0.1',
283               LocalPort => 8080,
284               Listen => 10,
285
286               # which certificate to offer
287               # with SNI support there can be different certificates per hostname
288               SSL_cert_file => 'cert.pem',
289               SSL_key_file => 'key.pem',
290           ) or die "failed to listen: $!";
291
292           # accept client
293           my $client = $server->accept or die
294               "failed to accept or ssl handshake: $!,$SSL_ERROR";
295
296       This will automatically use a secure set of ciphers and SSL version and
297       also supports Forward Secrecy with (Elliptic-Curve) Diffie-Hellmann Key
298       Exchange.
299
300       If you are doing a forking or threading server, we recommend that you
301       do the SSL handshake inside the new process/thread so that the master
302       is free for new connections.  We recommend this because a client with
303       improper or slow SSL handshake could make the server block in the
304       handshake which would be bad to do on the listening socket:
305
306           # inet server
307           my $server = IO::Socket::INET->new(
308               # where to listen
309               LocalAddr => '127.0.0.1',
310               LocalPort => 8080,
311               Listen => 10,
312           );
313
314           # accept client
315           my $client = $server->accept or die;
316
317           # SSL upgrade client (in new process/thread)
318           IO::Socket::SSL->start_SSL($client,
319               SSL_server => 1,
320               SSL_cert_file => 'cert.pem',
321               SSL_key_file => 'key.pem',
322           ) or die "failed to ssl handshake: $SSL_ERROR";
323
324       Like with normal sockets, neither forking nor threading servers scale
325       well.  It is recommended to use non-blocking sockets instead, see
326       "Using Non-Blocking Sockets"
327

Common Usage Errors

329       This is a list of typical errors seen with the use of IO::Socket::SSL:
330
331       ·   Disabling verification with "SSL_verify_mode".
332
333           As described in "Essential Information About SSL/TLS", a proper
334           identification of the peer is essential and failing to verify makes
335           Man-In-The-Middle attacks possible.
336
337           Nevertheless, lots of scripts and even public modules or
338           applications disable verification, because it is probably the
339           easiest way to make the thing work and usually nobody notices any
340           security problems anyway.
341
342           If the verification does not succeed with the default settings, one
343           can do the following:
344
345           ·       Make sure the needed CAs are in the store, maybe use
346                   "SSL_ca_file" or "SSL_ca_path" to specify a different CA
347                   store.
348
349           ·       If the validation fails because the certificate is self-
350                   signed and that's what you expect, you can use the
351                   "SSL_fingerprint" option to accept specific leaf
352                   certificates by their certificate or pubkey fingerprint.
353
354           ·       If the validation failed because the hostname does not
355                   match and you cannot access the host with the name given in
356                   the certificate, you can use "SSL_verifycn_name" to specify
357                   the hostname you expect in the certificate.
358
359           A common error pattern is also to disable verification if they
360           found no CA store (different modules look at different "default"
361           places).  Because IO::Socket::SSL is now able to provide a usable
362           CA store on most platforms (UNIX, Mac OSX and Windows) it is better
363           to use the defaults provided by IO::Socket::SSL.  If necessary
364           these can be checked with the "default_ca" method.
365
366       ·   Polling of SSL sockets (e.g. select, poll and other event loops).
367
368           If you sysread one byte on a normal socket it will result in a
369           syscall to read one byte. Thus, if more than one byte is available
370           on the socket it will be kept in the network stack of your OS and
371           the next select or poll call will return the socket as readable.
372           But, with SSL you don't deliver single bytes. Multiple data bytes
373           are packaged and encrypted together in an SSL frame. Decryption can
374           only be done on the whole frame, so a sysread for one byte actually
375           reads the complete SSL frame from the socket, decrypts it and
376           returns the first decrypted byte. Further sysreads will return more
377           bytes from the same frame until all bytes are returned and the next
378           SSL frame will be read from the socket.
379
380           Thus, in order to decide if you can read more data (e.g. if sysread
381           will block) you must check if there are still data in the current
382           SSL frame by calling "pending" and if there are no data pending you
383           might check the underlying socket with select or poll.  Another way
384           might be if you try to sysread at least 16kByte all the time.
385           16kByte is the maximum size of an SSL frame and because sysread
386           returns data from only a single SSL frame you can guarantee that
387           there are no pending data.
388
389           See also "Using Non-Blocking Sockets".
390
391       ·   Expecting exactly the same behavior as plain sockets.
392
393           IO::Socket::SSL tries to emulate the usual socket behavior as good
394           as possible, but full emulation can not be done. Specifically a
395           read on the SSL socket might also result in a write on the TCP
396           socket or a write on the SSL socket might result in a read on the
397           TCP socket. Also "accept" and close on the SSL socket will result
398           in writing and reading data to the TCP socket too.
399
400           Especially the hidden writes might result in a connection reset if
401           the underlying TCP socket is already closed by the peer. Unless
402           signal PIPE is explicitly handled by the application this will
403           ususally result in the application crashing. It is thus recommended
404           to explicitly IGNORE signal PIPE so that the errors get propagated
405           as EPIPE instead of causing a crash of the application.
406
407       ·   Set 'SSL_version' or 'SSL_cipher_list' to a "better" value.
408
409           IO::Socket::SSL tries to set these values to reasonable, secure
410           values which are compatible with the rest of the world.  But, there
411           are some scripts or modules out there which tried to be smart and
412           get more secure or compatible settings.  Unfortunately, they did
413           this years ago and never updated these values, so they are still
414           forced to do only 'TLSv1' (instead of also using TLSv12 or TLSv11).
415           Or they set 'HIGH' as the cipher list and thought they were secure,
416           but did not notice that 'HIGH' includes anonymous ciphers, e.g.
417           without identification of the peer.
418
419           So it is recommended to leave the settings at the secure defaults
420           which IO::Socket::SSL sets and which get updated from time to time
421           to better fit the real world.
422
423       ·   Make SSL settings inaccessible by the user, together with bad
424           builtin settings.
425
426           Some modules use IO::Socket::SSL, but don't make the SSL settings
427           available to the user. This is often combined with bad builtin
428           settings or defaults (like switching verification off).
429
430           Thus the user needs to hack around these restrictions by using
431           "set_args_filter_hack" or similar.
432
433       ·   Use of constants as strings.
434
435           Constants like "SSL_VERIFY_PEER" or "SSL_WANT_READ" should be used
436           as constants and not be put inside quotes, because they represent
437           numerical values.
438
439       ·   Forking and handling the socket in parent and child.
440
441           A fork of the process will duplicate the internal user space SSL
442           state of the socket. If both master and child interact with the
443           socket by using their own SSL state strange error messages will
444           happen. Such interaction includes explicit or implicit close of the
445           SSL socket. To avoid this the socket should be explicitly closed
446           with SSL_no_shutdown.
447
448       ·   Forking and executing a new process.
449
450           Since the SSL state is stored in user space it will be duplicated
451           by a fork but it will be lost when doing exec. This means it is not
452           possible to simply redirect stdin and stdout for the new process to
453           the SSL socket by duplicating the relevant file handles. Instead
454           explicitly exchanging plain data between child-process and SSL
455           socket are needed.
456

Common Problems with SSL

458       SSL is a complex protocol with multiple implementations and each of
459       these has their own quirks. While most of these implementations work
460       together, it often gets problematic with older versions, minimal
461       versions in load balancers, or plain wrong setups.
462
463       Unfortunately these problems are hard to debug.  Helpful for debugging
464       are a knowledge of SSL internals, wireshark and the use of the debug
465       settings of IO::Socket::SSL and Net::SSLeay, which can both be set with
466       $IO::Socket::SSL::DEBUG.  The following debugs levels are defined, but
467       used not in any consistent way:
468
469       ·   0 - No debugging (default).
470
471       ·   1 - Print out errors from IO::Socket::SSL and ciphers from
472           Net::SSLeay.
473
474       ·   2 - Print also information about call flow from IO::Socket::SSL and
475           progress information from Net::SSLeay.
476
477       ·   3 - Print also some data dumps from IO::Socket::SSL and from
478           Net::SSLeay.
479
480       Also, "analyze-ssl.pl" from the ssl-tools repository at
481       <https://github.com/noxxi/p5-ssl-tools>  might be a helpful tool when
482       debugging SSL problems, as do the "openssl" command line tool and a
483       check with a different SSL implementation (e.g. a web browser).
484
485       The following problems are not uncommon:
486
487       ·   Bad server setup: missing intermediate certificates.
488
489           It is a regular problem that administrators fail to include all
490           necessary certificates into their server setup, e.g. everything
491           needed to build the trust chain from the trusted root.  If they
492           check the setup with the browser everything looks ok, because
493           browsers work around these problems by caching any intermediate
494           certificates and apply them to new connections if certificates are
495           missing.
496
497           But, fresh browser profiles which have never seen these
498           intermediates cannot fill in the missing certificates and fail to
499           verify; the same is true with IO::Socket::SSL.
500
501       ·   Old versions of servers or load balancers which do not understand
502           specific TLS versions or croak on specific data.
503
504           From time to time one encounters an SSL peer, which just closes the
505           connection inside the SSL handshake. This can usually be worked
506           around by downgrading the SSL version, e.g. by setting
507           "SSL_version". Modern Browsers usually deal with such servers by
508           automatically downgrading the SSL version and repeat the connection
509           attempt until they succeed.
510
511           Worse servers do not close the underlying TCP connection but
512           instead just drop the relevant packet. This is harder to detect
513           because it looks like a stalled connection. But downgrading the SSL
514           version often works here too.
515
516           A cause of such problems are often load balancers or security
517           devices, which have hardware acceleration and only a minimal (and
518           less robust) SSL stack. They can often be detected because they
519           support much fewer ciphers than other implementations.
520
521       ·   Bad or old OpenSSL versions.
522
523           IO::Socket::SSL uses OpenSSL with the help of the Net::SSLeay
524           library. It is recommend to have a recent version of this library,
525           because it has more features and usually fewer known bugs.
526
527       ·   Validation of client certificates fail.
528
529           Make sure that the purpose of the certificate allows use as ssl
530           client (check with "openssl x509 -purpose", that the necessary root
531           certificate is in the path specified by "SSL_ca*" (or the default
532           path) and that any intermediate certificates needed to build the
533           trust chain are sent by the client.
534
535       ·   Validation of self-signed certificate fails even if it is given
536           with "SSL_ca*" argument.
537
538           The "SSL_ca*" arguments do not give a general trust store for
539           arbitrary certificates but only specify a store for CA certificates
540           which then can be used to verify other certificates.  This
541           especially means that certificates which are not a CA get simply
542           ignored, notably self-signed certificates which do not also have
543           the CA-flag set.
544
545           This behavior of OpenSSL differs from the more general trust-store
546           concept which can be found in browsers and where it is possible to
547           simply added arbitrary certificates (CA or not) as trusted.
548

Using Non-Blocking Sockets

550       If you have a non-blocking socket, the expected behavior on read,
551       write, accept or connect is to set $! to EWOULDBLOCK if the operation
552       cannot be completed immediately. Note that EWOULDBLOCK is the same as
553       EAGAIN on UNIX systems, but is different on Windows.
554
555       With SSL, handshakes might occur at any time, even within an
556       established connection. In these cases it is necessary to finish the
557       handshake before you can read or write data. This might result in
558       situations where you want to read but must first finish the write of a
559       handshake or where you want to write but must first finish a read.  In
560       these cases $! is set to EAGAIN like expected, and additionally
561       $SSL_ERROR is set to either SSL_WANT_READ or SSL_WANT_WRITE.  Thus if
562       you get EWOULDBLOCK on a SSL socket you must check $SSL_ERROR for
563       SSL_WANT_* and adapt your event mask accordingly.
564
565       Using readline on non-blocking sockets does not make much sense and I
566       would advise against using it.  And, while the behavior is not
567       documented for other IO::Socket classes, it will try to emulate the
568       behavior seen there, e.g. to return the received data instead of
569       blocking, even if the line is not complete. If an unrecoverable error
570       occurs it will return nothing, even if it already received some data.
571
572       Also, I would advise against using "accept" with a non-blocking SSL
573       object because it might block and this is not what most would expect.
574       The reason for this is that "accept" on a non-blocking TCP socket (e.g.
575       IO::Socket::IP, IO::Socket::INET..) results in a new TCP socket which
576       does not inherit the non-blocking behavior of the master socket. And
577       thus, the initial SSL handshake on the new socket inside
578       "IO::Socket::SSL::accept" will be done in a blocking way. To work
579       around this you are safer by doing a TCP accept and later upgrade the
580       TCP socket in a non-blocking way with "start_SSL" and "accept_SSL".
581
582           my $cl = IO::Socket::SSL->new($dst);
583           $cl->blocking(0);
584           my $sel = IO::Select->new($cl);
585           while (1) {
586               # with SSL a call for reading n bytes does not result in reading of n
587               # bytes from the socket, but instead it must read at least one full SSL
588               # frame. If the socket has no new bytes, but there are unprocessed data
589               # from the SSL frame can_read will block!
590
591               # wait for data on socket
592               $sel->can_read();
593
594               # new data on socket or eof
595               READ:
596               # this does not read only 1 byte from socket, but reads the complete SSL
597               # frame and then just returns one byte. On subsequent calls it than
598               # returns more byte of the same SSL frame until it needs to read the
599               # next frame.
600               my $n = sysread( $cl,my $buf,1);
601               if ( ! defined $n ) {
602                   die $! if not ${EWOULDBLOCK};
603                   next if $SSL_ERROR == SSL_WANT_READ;
604                   if ( $SSL_ERROR == SSL_WANT_WRITE ) {
605                       # need to write data on renegotiation
606                       $sel->can_write;
607                       next;
608                   }
609                   die "something went wrong: $SSL_ERROR";
610               } elsif ( ! $n ) {
611                   last; # eof
612               } else {
613                   # read next bytes
614                   # we might have still data within the current SSL frame
615                   # thus first process these data instead of waiting on the underlying
616                   # socket object
617                   goto READ if $cl->pending;    # goto sysread
618                   next;                         # goto $sel->can_read
619               }
620           }
621
622       Additionally there are differences to plain sockets when using select,
623       poll, kqueue or similar technologies to get notified if data are
624       available.  Relying only on these calls is not sufficient in all cases
625       since unread data might be internally buffered in the SSL stack. To
626       detect such buffering pending() need to be used. Alternatively the
627       buffering can be avoided by using sysread with the maximum size of an
628       SSL frame. See "Common Usage Errors" for details.
629

Advanced Usage

631   SNI Support
632       Newer extensions to SSL can distinguish between multiple hostnames on
633       the same IP address using Server Name Indication (SNI).
634
635       Support for SNI on the client side was added somewhere in the OpenSSL
636       0.9.8 series, but with 1.0 a bug was fixed when the server could not
637       decide about its hostname. Therefore client side SNI is only supported
638       with OpenSSL 1.0 or higher in IO::Socket::SSL.  With a supported
639       version, SNI is used automatically on the client side, if it can
640       determine the hostname from "PeerAddr" or "PeerHost" (which are
641       synonyms in the underlying IO::Socket:: classes and thus should never
642       be set both or at least not to different values).  On unsupported
643       OpenSSL versions it will silently not use SNI.  The hostname can also
644       be given explicitly given with "SSL_hostname", but in this case it will
645       throw in error, if SNI is not supported.  To check for support you
646       might call "IO::Socket::SSL->can_client_sni()".
647
648       On the server side, earlier versions of OpenSSL are supported, but only
649       together with Net::SSLeay version >= 1.50.  To check for support you
650       might call "IO::Socket::SSL->can_server_sni()".  If server side SNI is
651       supported, you might specify different certificates per host with
652       "SSL_cert*" and "SSL_key*", and check the requested name using
653       "get_servername".
654
655   Talk Plain and SSL With The Same Socket
656       It is often required to first exchange some plain data and then upgrade
657       the socket to SSL after some kind of STARTTLS command. Protocols like
658       FTPS even need a way to downgrade the socket again back to plain.
659
660       The common way to do this would be to create a normal socket and use
661       "start_SSL" to upgrade and stop_SSL to downgrade:
662
663           my $sock = IO::Socket::INET->new(...) or die $!;
664           ... exchange plain data on $sock until starttls command ...
665           IO::Socket::SSL->start_SSL($sock,%sslargs) or die $SSL_ERROR;
666           ... now $sock is an IO::Socket::SSL object ...
667           ... exchange data with SSL on $sock until stoptls command ...
668           $sock->stop_SSL or die $SSL_ERROR;
669           ... now $sock is again an IO::Socket::INET object ...
670
671       But, lots of modules just derive directly from IO::Socket::INET.  While
672       this base class can be replaced with IO::Socket::SSL, these modules
673       cannot easily support different base classes for SSL and plain data and
674       switch between these classes on a starttls command.
675
676       To help in this case, IO::Socket::SSL can be reduced to a plain socket
677       on startup, and connect_SSL/accept_SSL/start_SSL can be used to enable
678       SSL and "stop_SSL" to talk plain again:
679
680           my $sock = IO::Socket::SSL->new(
681               PeerAddr => ...
682               SSL_startHandshake => 0,
683               %sslargs
684           ) or die $!;
685           ... exchange plain data on $sock until starttls command ...
686           $sock->connect_SSL or die $SSL_ERROR;
687           ... now $sock is an IO::Socket::SSL object ...
688           ... exchange data with SSL on $sock until stoptls command ...
689           $sock->stop_SSL or die $SSL_ERROR;
690           ... $sock is still an IO::Socket::SSL object ...
691           ... but data exchanged again in plain ...
692

Integration Into Own Modules

694       IO::Socket::SSL behaves similarly to other IO::Socket modules and thus
695       could be integrated in the same way, but you have to take special care
696       when using non-blocking I/O (like for handling timeouts) or using
697       select or poll.  Please study the documentation on how to deal with
698       these differences.
699
700       Also, it is recommended to not set or touch most of the "SSL_*"
701       options, so that they keep their secure defaults. It is also
702       recommended to let the user override these SSL specific settings
703       without the need of global settings or hacks like
704       "set_args_filter_hack".
705
706       The notable exception is "SSL_verifycn_scheme".  This should be set to
707       the hostname verification scheme required by the module or protocol.
708

Description Of Methods

710       IO::Socket::SSL inherits from another IO::Socket module.  The choice of
711       the super class depends on the installed modules:
712
713       ·   If IO::Socket::IP with at least version 0.20 is installed it will
714           use this module as super class, transparently providing IPv6 and
715           IPv4 support.
716
717       ·   If IO::Socket::INET6 is installed it will use this module as super
718           class, transparently providing IPv6 and IPv4 support.
719
720       ·   Otherwise it will fall back to IO::Socket::INET, which is a perl
721           core module.  With IO::Socket::INET you only get IPv4 support.
722
723       Please be aware that with the IPv6 capable super classes, it will look
724       first for the IPv6 address of a given hostname. If the resolver
725       provides an IPv6 address, but the host cannot be reached by IPv6, there
726       will be no automatic fallback to IPv4.  To avoid these problems you can
727       enforce IPv4 for a specific socket by using the "Domain" or "Family"
728       option with the value AF_INET as described in IO::Socket::IP.
729       Alternatively you can enforce IPv4 globally by loading IO::Socket::SSL
730       with the option 'inet4', in which case it will use the IPv4 only class
731       IO::Socket::INET as the super class.
732
733       IO::Socket::SSL will provide all of the methods of its super class, but
734       sometimes it will override them to match the behavior expected from SSL
735       or to provide additional arguments.
736
737       The new or changed methods are described below, but please also read
738       the section about SSL specific error handling.
739
740       Error Handling
741           If an SSL specific error occurs, the global variable $SSL_ERROR
742           will be set.  If the error occurred on an existing SSL socket, the
743           method "errstr" will give access to the latest socket specific
744           error.  Both $SSL_ERROR and the "errstr" method give a dualvar
745           similar to $!, e.g.  providing an error number in numeric context
746           or an error description in string context.
747
748       new(...)
749           Creates a new IO::Socket::SSL object.  You may use all the friendly
750           options that came bundled with the super class (e.g.
751           IO::Socket::IP, IO::Socket::INET, ...) plus (optionally) the ones
752           described below.  If you don't specify any SSL related options it
753           will do its best in using secure defaults, e.g. choosing good
754           ciphers, enabling proper verification, etc.
755
756           SSL_server
757             Set this option to a true value if the socket should be used as a
758             server.  If this is not explicitly set it is assumed if the
759             "Listen" parameter is given when creating the socket.
760
761           SSL_hostname
762             This can be given to specify the hostname used for SNI, which is
763             needed if you have multiple SSL hostnames on the same IP address.
764             If not given it will try to determine the hostname from
765             "PeerAddr", which will fail if only an IP was given or if this
766             argument is used within "start_SSL".
767
768             If you want to disable SNI, set this argument to ''.
769
770             Currently only supported for the client side and will be ignored
771             for the server side.
772
773             See section "SNI Support" for details of SNI the support.
774
775           SSL_startHandshake
776             If this option is set to false (defaults to true) it will not
777             start the SSL handshake yet. This has to be done later with
778             "accept_SSL" or "connect_SSL".  Before the handshake is started
779             read/write/etc. can be used to exchange plain data.
780
781           SSL_keepSocketOnError
782             If this option is set to true (defaults to false) it will not
783             close the underlying TCP socket on errors. In most cases there is
784             no real use for this behavior since both sides of the TCP
785             connection will probably have a different idea of the current
786             state of the connection.
787
788           SSL_ca | SSL_ca_file | SSL_ca_path
789             Usually you want to verify that the peer certificate has been
790             signed by a trusted certificate authority. In this case you
791             should use this option to specify the file ("SSL_ca_file") or
792             directory ("SSL_ca_path") containing the certificate(s) of the
793             trusted certificate authorities.
794
795             "SSL_ca_path" can also be an array or a string containing
796             multiple path, where the path are separated by the platform
797             specific separator. This separator is ";" on DOS, Windows,
798             Netware, "," on VMS and ":" for all the other systems.  If
799             multiple path are given at least one of these must be accessible.
800
801             You can also give a list of X509* certificate handles (like you
802             get from Net::SSLeay or IO::Socket::SSL::Utils::PEM_xxx2cert)
803             with "SSL_ca". These will be added to the CA store before path
804             and file and thus take precedence.  If neither SSL_ca, nor
805             SSL_ca_file or SSL_ca_path are set it will use "default_ca()" to
806             determine the user-set or system defaults.  If you really don't
807             want to set a CA set SSL_ca_file or SSL_ca_path to "\undef" or
808             SSL_ca to an empty list. (unfortunately '' is used by some
809             modules using IO::Socket::SSL when CA is not explicitly given).
810
811           SSL_client_ca | SSL_client_ca_file
812             If verify_mode is VERIFY_PEER on the server side these options
813             can be used to set the list of acceptable CAs for the client.
814             This way the client can select they required certificate from a
815             list of certificates.  The value for these options is similar to
816             "SSL_ca" and "SSL_ca_file".
817
818           SSL_fingerprint
819             Sometimes you have a self-signed certificate or a certificate
820             issued by an unknown CA and you really want to accept it, but
821             don't want to disable verification at all. In this case you can
822             specify the fingerprint of the certificate as
823             'algo$hex_fingerprint'. "algo" is a fingerprint algorithm
824             supported by OpenSSL, e.g. 'sha1','sha256'... and
825             "hex_fingerprint" is the hexadecimal representation of the binary
826             fingerprint. Any colons inside the hex string will be ignored.
827
828             If you want to use the fingerprint of the pubkey inside the
829             certificate instead of the certificate use the syntax
830             'algo$pub$hex_fingerprint' instead.  To get the fingerprint of an
831             established connection you can use "get_fingerprint".
832
833             It is also possible to skip "algo$", i.e. only specifiy the
834             fingerprint. In this case the likely algorithms will be
835             automatically detected based on the length of the digest string.
836
837             You can specify a list of fingerprints in case you have several
838             acceptable certificates.  If a fingerprint matches the topmost
839             (i.e. leaf) certificate no additional validations can make the
840             verification fail.
841
842           SSL_cert_file | SSL_cert | SSL_key_file | SSL_key
843             If you create a server you usually need to specify a server
844             certificate which should be verified by the client. Same is true
845             for client certificates, which should be verified by the server.
846             The certificate can be given as a file with SSL_cert_file or as
847             an internal representation of an X509* object (like you get from
848             Net::SSLeay or IO::Socket::SSL::Utils::PEM_xxx2cert) with
849             SSL_cert.  If given as a file it will automatically detect the
850             format.  Supported file formats are PEM, DER and PKCS#12, where
851             PEM and PKCS#12 can contain the certificate and the chain to use,
852             while DER can only contain a single certificate.
853
854             If given as a list of X509* please note, that the all the chain
855             certificates (e.g. all except the first) will be "consumed" by
856             openssl and will be freed if the SSL context gets destroyed - so
857             you should never free them yourself. But the servers certificate
858             (e.g. the first) will not be consumed by openssl and thus must be
859             freed by the application.
860
861             For each certificate a key is need, which can either be given as
862             a file with SSL_key_file or as an internal representation of an
863             EVP_PKEY* object with SSL_key (like you get from Net::SSLeay or
864             IO::Socket::SSL::Utils::PEM_xxx2key).  If a key was already given
865             within the PKCS#12 file specified by SSL_cert_file it will ignore
866             any SSL_key or SSL_key_file.  If no SSL_key or SSL_key_file was
867             given it will try to use the PEM file given with SSL_cert_file
868             again, maybe it contains the key too.
869
870             If your SSL server should be able to use different certificates
871             on the same IP address, depending on the name given by SNI, you
872             can use a hash reference instead of a file with "<hostname ="
873             cert_file>>.
874
875             If your SSL server should be able to use both RSA and ECDSA
876             certificates for the same domain/IP a similar hash reference like
877             with SNI is given. The domain names used to specify the
878             additional certificates should be "hostname%whatever", i.e.
879             "hostname%ecc" or similar. This needs at least OpenSSL 1.0.2. To
880             let the server pick the certificate based on the clients cipher
881             preference "SSL_honor_cipher_order" should be set to false.
882
883             In case certs and keys are needed but not given it might fall
884             back to builtin defaults, see "Defaults for Cert, Key and CA".
885
886             Examples:
887
888              SSL_cert_file => 'mycert.pem',
889              SSL_key_file => 'mykey.pem',
890
891              SSL_cert_file => {
892                 "foo.example.org" => 'foo-cert.pem',
893                 "foo.example.org%ecc" => 'foo-ecc-cert.pem',
894                 "bar.example.org" => 'bar-cert.pem',
895                 # used when nothing matches or client does not support SNI
896                 '' => 'default-cert.pem',
897                 '%ecc' => 'default-ecc-cert.pem',
898              },
899              SSL_key_file => {
900                 "foo.example.org" => 'foo-key.pem',
901                 "foo.example.org%ecc" => 'foo-ecc-key.pem',
902                 "bar.example.org" => 'bar-key.pem',
903                 # used when nothing matches or client does not support SNI
904                 '' => 'default-key.pem',
905                 '%ecc' => 'default-ecc-key.pem',
906              }
907
908           SSL_passwd_cb
909             If your private key is encrypted, you might not want the default
910             password prompt from Net::SSLeay.  This option takes a reference
911             to a subroutine that should return the password required to
912             decrypt your private key.
913
914           SSL_use_cert
915             If this is true, it forces IO::Socket::SSL to use a certificate
916             and key, even if you are setting up an SSL client.  If this is
917             set to 0 (the default), then you will only need a certificate and
918             key if you are setting up a server.
919
920             SSL_use_cert will implicitly be set if SSL_server is set.  For
921             convenience it is also set if it was not given but a cert was
922             given for use (SSL_cert_file or similar).
923
924           SSL_version
925             Sets the version of the SSL protocol used to transmit data.
926             'SSLv23' uses a handshake compatible with SSL2.0, SSL3.0 and
927             TLS1.x, while 'SSLv2', 'SSLv3', 'TLSv1', 'TLSv1_1', 'TLSv1_2', or
928             'TLSv1_3' restrict handshake and protocol to the specified
929             version.  All values are case-insensitive.  Instead of 'TLSv1_1',
930             'TLSv1_2', and 'TLSv1_3' one can also use 'TLSv11', 'TLSv12', and
931             'TLSv13'.  Support for 'TLSv1_1', 'TLSv1_2', and 'TLSv1_3'
932             requires recent versions of Net::SSLeay and openssl.  The default
933             SSL_version is defined by the underlying cryptographic library.
934
935             Independent from the handshake format you can limit to set of
936             accepted SSL versions by adding !version separated by ':'.
937
938             For example, 'SSLv23:!SSLv3:!SSLv2' means that the handshake
939             format is compatible to SSL2.0 and higher, but that the
940             successful handshake is limited to TLS1.0 and higher, that is no
941             SSL2.0 or SSL3.0 because both of these versions have serious
942             security issues and should not be used anymore.  You can also use
943             !TLSv1_1 and !TLSv1_2 to disable TLS versions 1.1 and 1.2 while
944             still allowing TLS version 1.0.
945
946             Setting the version instead to 'TLSv1' might break interaction
947             with older clients, which need and SSL2.0 compatible handshake.
948             On the other side some clients just close the connection when
949             they receive a TLS version 1.1 request. In this case setting the
950             version to 'SSLv23:!SSLv2:!SSLv3:!TLSv1_1:!TLSv1_2' might help.
951
952           SSL_cipher_list
953             If this option is set the cipher list for the connection will be
954             set to the given value, e.g. something like
955             'ALL:!LOW:!EXP:!aNULL'. Look into the OpenSSL documentation
956             (<http://www.openssl.org/docs/apps/ciphers.html#CIPHER_STRINGS>)
957             for more details.
958
959             Unless you fail to contact your peer because of no shared ciphers
960             it is recommended to leave this option at the default setting,
961             which honors the system-wide PROFILE=SYSTEM cipher list.
962
963             In case different cipher lists are needed for different SNI hosts
964             a hash can be given with the host as key and the cipher suite as
965             value, similar to SSL_cert*.
966
967           SSL_honor_cipher_order
968             If this option is true the cipher order the server specified is
969             used instead of the order proposed by the client. This option
970             defaults to true to make use of our secure cipher list setting.
971
972           SSL_dh_file
973             To create a server which provides forward secrecy you need to
974             either give the DH parameters or (better, because faster) the
975             ECDH curve. This setting cares about DH parameters.
976
977             To support non-elliptic Diffie-Hellman key exchange a suitable
978             file needs to be given here or the SSL_dh should be used with a
979             appropriate value.  See dhparam command in openssl for more
980             information.
981
982             If neither "SSL_dh_file" nor "SSL_dh" are set a builtin DH
983             parameter with a length of 2048 bit is used to offer DH key
984             exchange by default. If you don't want this (e.g. disable DH key
985             exchange) explicitly set this or the "SSL_dh" parameter to undef.
986
987           SSL_dh
988             Like SSL_dh_file, but instead of giving a file you use a
989             preloaded or generated DH*.
990
991           SSL_ecdh_curve
992             To create a server which provides forward secrecy you need to
993             either give the DH parameters or (better, because faster) the
994             ECDH curve. This setting cares about the ECDH curve(s).
995
996             To support Elliptic Curve Diffie-Hellmann key exchange the OID or
997             NID of at least one suitable curve needs to be provided here.
998
999             With OpenSSL 1.1.0+ this parameter defaults to "auto", which
1000             means that it lets OpenSSL pick the best settings. If support for
1001             CTX_set_ecdh_auto is implemented in Net::SSLeay (needs at least
1002             version 1.86) it will use this to implement the same default.
1003             Otherwise it will default to "prime256v1" (builtin of OpenSSL) in
1004             order to offer ECDH key exchange by default.
1005
1006             If setting groups or curves is supported by Net::SSLeay (needs at
1007             least version 1.86) then multiple curves can be given here in the
1008             order of the preference, i.e.  "P-521:P-384:P-256". When used at
1009             the client side this will include the supported curves as
1010             extension in the TLS handshake.
1011
1012             If you don't want to have ECDH key exchange this could be set to
1013             undef or set "SSL_ciphers" to exclude all of these ciphers.
1014
1015             You can check if ECDH support is available by calling
1016             "IO::Socket::SSL->can_ecdh".
1017
1018           SSL_verify_mode
1019             This option sets the verification mode for the peer certificate.
1020             You may combine SSL_VERIFY_PEER (verify_peer),
1021             SSL_VERIFY_FAIL_IF_NO_PEER_CERT (fail verification if no peer
1022             certificate exists; ignored for clients), SSL_VERIFY_CLIENT_ONCE
1023             (verify client once; ignored for clients).  See OpenSSL man page
1024             for SSL_CTX_set_verify for more information.
1025
1026             The default is SSL_VERIFY_NONE for server  (e.g. no check for
1027             client certificate) and SSL_VERIFY_PEER for client (check server
1028             certificate).
1029
1030           SSL_verify_callback
1031             If you want to verify certificates yourself, you can pass a sub
1032             reference along with this parameter to do so.  When the callback
1033             is called, it will be passed:
1034
1035             1. a true/false value that indicates what OpenSSL thinks of the
1036             certificate,
1037             2. a C-style memory address of the certificate store,
1038             3. a string containing the certificate's issuer attributes and
1039             owner attributes, and
1040             4. a string containing any errors encountered (0 if no errors).
1041             5. a C-style memory address of the peer's own certificate
1042             (convertible to PEM form with
1043             Net::SSLeay::PEM_get_string_X509()).
1044             6. The depth of the certificate in the chain. Depth 0 is the leaf
1045             certificate.
1046
1047             The function should return 1 or 0, depending on whether it thinks
1048             the certificate is valid or invalid.  The default is to let
1049             OpenSSL do all of the busy work.
1050
1051             The callback will be called for each element in the certificate
1052             chain.
1053
1054             See the OpenSSL documentation for SSL_CTX_set_verify for more
1055             information.
1056
1057           SSL_verifycn_scheme
1058             The scheme is used to correctly verify the identity inside the
1059             certificate by using the hostname of the peer.  See the
1060             information about the verification schemes in verify_hostname.
1061
1062             If you don't specify a scheme it will use 'default', but only
1063             complain loudly if the name verification fails instead of letting
1064             the whole certificate verification fail. THIS WILL CHANGE, e.g.
1065             it will let the certificate verification fail in the future if
1066             the hostname does not match the certificate !!!!  To override the
1067             name used in verification use SSL_verifycn_name.
1068
1069             The scheme 'default' is a superset of the usual schemes, which
1070             will accept the hostname in common name and subjectAltName and
1071             allow wildcards everywhere.  While using this scheme is way more
1072             secure than no name verification at all you better should use the
1073             scheme specific to your application protocol, e.g. 'http',
1074             'ftp'...
1075
1076             If you are really sure, that you don't want to verify the
1077             identity using the hostname  you can use 'none' as a scheme. In
1078             this case you'd better have alternative forms of verification,
1079             like a certificate fingerprint or do a manual verification later
1080             by calling verify_hostname yourself.
1081
1082           SSL_verifycn_publicsuffix
1083             This option is used to specify the behavior when checking
1084             wildcards certificates for public suffixes, e.g. no wildcard
1085             certificates for *.com or *.co.uk should be accepted, while
1086             *.example.com or *.example.co.uk is ok.
1087
1088             If not specified it will simply use the builtin default of
1089             IO::Socket::SSL::PublicSuffix, you can create another object with
1090             from_string or from_file of this module.
1091
1092             To disable verification of public suffix set this option to ''.
1093
1094           SSL_verifycn_name
1095             Set the name which is used in verification of hostname. If
1096             SSL_verifycn_scheme is set and no SSL_verifycn_name is given it
1097             will try to use SSL_hostname or PeerHost and PeerAddr settings
1098             and fail if no name can be determined.  If SSL_verifycn_scheme is
1099             not set it will use a default scheme and warn if it cannot
1100             determine a hostname, but it will not fail.
1101
1102             Using PeerHost or PeerAddr works only if you create the
1103             connection directly with "IO::Socket::SSL->new", if an
1104             IO::Socket::INET object is upgraded with start_SSL the name has
1105             to be given in SSL_verifycn_name or SSL_hostname.
1106
1107           SSL_check_crl
1108             If you want to verify that the peer certificate has not been
1109             revoked by the signing authority, set this value to true. OpenSSL
1110             will search for the CRL in your SSL_ca_path, or use the file
1111             specified by SSL_crl_file.  See the Net::SSLeay documentation for
1112             more details.  Note that this functionality appears to be broken
1113             with OpenSSL < v0.9.7b, so its use with lower versions will
1114             result in an error.
1115
1116           SSL_crl_file
1117             If you want to specify the CRL file to be used, set this value to
1118             the pathname to be used.  This must be used in addition to
1119             setting SSL_check_crl.
1120
1121           SSL_ocsp_mode
1122             Defines how certificate revocation is done using OCSP (Online
1123             Status Revocation Protocol). The default is to send a request for
1124             OCSP stapling to the server and if the server sends an OCSP
1125             response back the result will be used.
1126
1127             Any other OCSP checking needs to be done manually with
1128             "ocsp_resolver".
1129
1130             The following flags can be combined with "|":
1131
1132             SSL_OCSP_NO_STAPLE
1133                     Don't ask for OCSP stapling.  This is the default if
1134                     SSL_verify_mode is VERIFY_NONE.
1135
1136             SSL_OCSP_TRY_STAPLE
1137                     Try OCSP stapling, but don't complain if it gets no
1138                     stapled response back.  This is the default if
1139                     SSL_verify_mode is VERIFY_PEER (the default).
1140
1141             SSL_OCSP_MUST_STAPLE
1142                     Consider it a hard error, if the server does not send a
1143                     stapled OCSP response back. Most servers currently send
1144                     no stapled OCSP response back.
1145
1146             SSL_OCSP_FAIL_HARD
1147                     Fail hard on response errors, default is to fail soft
1148                     like the browsers do.  Soft errors mean, that the OCSP
1149                     response is not usable, e.g. no response, error response,
1150                     no valid signature etc.  Certificate revocations inside a
1151                     verified response are considered hard errors in any case.
1152
1153                     Soft errors inside a stapled response are never
1154                     considered hard, e.g. it is expected that in this case an
1155                     OCSP request will be send to the responsible OCSP
1156                     responder.
1157
1158             SSL_OCSP_FULL_CHAIN
1159                     This will set up the "ocsp_resolver" so that all
1160                     certificates from the peer chain will be checked,
1161                     otherwise only the leaf certificate will be checked
1162                     against revocation.
1163
1164           SSL_ocsp_staple_callback
1165             If this callback is defined, it will be called with the SSL
1166             object and the OCSP response handle obtained from the peer, e.g.
1167             "<$cb-"($ssl,$resp)>>.  If the peer did not provide a stapled
1168             OCSP response the function will be called with "$resp=undef".
1169             Because the OCSP response handle is no longer valid after leaving
1170             this function it should not by copied or freed. If access to the
1171             response is necessary after leaving this function it can be
1172             serialized with "Net::SSLeay::i2d_OCSP_RESPONSE".
1173
1174             If no such callback is provided, it will use the default one,
1175             which verifies the response and uses it to check if the
1176             certificate(s) of the connection got revoked.
1177
1178           SSL_ocsp_cache
1179             With this option a cache can be given for caching OCSP responses,
1180             which could be shared between different SSL contexts. If not
1181             given a cache specific to the SSL context only will be used.
1182
1183             You can either create a new cache with
1184             "IO::Socket::SSL::OCSP_Cache->new([size])" or implement your own
1185             cache, which needs to have methods "put($key,\%entry)" and
1186             "get($key)" (returning "\%entry") where entry is the hash
1187             representation of the OCSP response with fields like
1188             "nextUpdate". The default implementation of the cache will
1189             consider responses valid as long as "nextUpdate" is less then the
1190             current time.
1191
1192           SSL_reuse_ctx
1193             If you have already set the above options for a previous instance
1194             of IO::Socket::SSL, then you can reuse the SSL context of that
1195             instance by passing it as the value for the SSL_reuse_ctx
1196             parameter.  You may also create a new instance of the
1197             IO::Socket::SSL::SSL_Context class, using any context options
1198             that you desire without specifying connection options, and pass
1199             that here instead.
1200
1201             If you use this option, all other context-related options that
1202             you pass in the same call to new() will be ignored unless the
1203             context supplied was invalid.  Note that, contrary to versions of
1204             IO::Socket::SSL below v0.90, a global SSL context will not be
1205             implicitly used unless you use the set_default_context()
1206             function.
1207
1208           SSL_create_ctx_callback
1209             With this callback you can make individual settings to the
1210             context after it got created and the default setup was done.  The
1211             callback will be called with the CTX object from Net::SSLeay as
1212             the single argument.
1213
1214             Example for limiting the server session cache size:
1215
1216               SSL_create_ctx_callback => sub {
1217                   my $ctx = shift;
1218                   Net::SSLeay::CTX_sess_set_cache_size($ctx,128);
1219               }
1220
1221           SSL_session_cache_size
1222             If you make repeated connections to the same host/port and the
1223             SSL renegotiation time is an issue, you can turn on client-side
1224             session caching with this option by specifying a positive cache
1225             size.  For successive connections, pass the SSL_reuse_ctx option
1226             to the new() calls (or use set_default_context()) to make use of
1227             the cached sessions.  The session cache size refers to the number
1228             of unique host/port pairs that can be stored at one time; the
1229             oldest sessions in the cache will be removed if new ones are
1230             added.
1231
1232             This option does not effect the session cache a server has for
1233             it's clients, e.g. it does not affect SSL objects with SSL_server
1234             set.
1235
1236             Note that session caching with TLS 1.3 needs at least Net::SSLeay
1237             1.86.
1238
1239           SSL_session_cache
1240             Specifies session cache object which should be used instead of
1241             creating a new.  Overrules SSL_session_cache_size.  This option
1242             is useful if you want to reuse the cache, but not the rest of the
1243             context.
1244
1245             A session cache object can be created using
1246             "IO::Socket::SSL::Session_Cache->new( cachesize )".
1247
1248             Use set_default_session_cache() to set a global cache object.
1249
1250           SSL_session_key
1251             Specifies a key to use for lookups and inserts into client-side
1252             session cache.  Per default ip:port of destination will be used,
1253             but sometimes you want to share the same session over multiple
1254             ports on the same server (like with FTPS).
1255
1256           SSL_session_id_context
1257             This gives an id for the servers session cache. It's necessary if
1258             you want clients to connect with a client certificate. If not
1259             given but SSL_verify_mode specifies the need for client
1260             certificate a context unique id will be picked.
1261
1262           SSL_error_trap
1263             When using the accept() or connect() methods, it may be the case
1264             that the actual socket connection works but the SSL negotiation
1265             fails, as in the case of an HTTP client connecting to an HTTPS
1266             server.  Passing a subroutine ref attached to this parameter
1267             allows you to gain control of the orphaned socket instead of
1268             having it be closed forcibly.  The subroutine, if called, will be
1269             passed two parameters: a reference to the socket on which the SSL
1270             negotiation failed and the full text of the error message.
1271
1272           SSL_npn_protocols
1273             If used on the server side it specifies list of protocols
1274             advertised by SSL server as an array ref, e.g.
1275             ['spdy/2','http1.1'].  On the client side it specifies the
1276             protocols offered by the client for NPN as an array ref.  See
1277             also method "next_proto_negotiated".
1278
1279             Next Protocol Negotiation (NPN) is available with Net::SSLeay
1280             1.46+ and openssl-1.0.1+. NPN is unavailable in TLSv1.3 protocol.
1281             To check support you might call "IO::Socket::SSL->can_npn()".  If
1282             you use this option with an unsupported Net::SSLeay/OpenSSL it
1283             will throw an error.
1284
1285           SSL_alpn_protocols
1286             If used on the server side it specifies list of protocols
1287             supported by the SSL server as an array ref, e.g. ['http/2.0',
1288             'spdy/3.1','http/1.1'].  On the client side it specifies the
1289             protocols advertised by the client for ALPN as an array ref.  See
1290             also method "alpn_selected".
1291
1292             Application-Layer Protocol Negotiation (ALPN) is available with
1293             Net::SSLeay 1.56+ and openssl-1.0.2+. More details about the
1294             extension are in RFC7301. To check support you might call
1295             "IO::Socket::SSL->can_alpn()". If you use this option with an
1296             unsupported Net::SSLeay/OpenSSL it will throw an error.
1297
1298             Note that some client implementations may encounter problems if
1299             both NPN and ALPN are specified. Since ALPN is intended as a
1300             replacement for NPN, try providing ALPN protocols then fall back
1301             to NPN if that fails.
1302
1303           SSL_ticket_keycb => [$sub,$data] | $sub
1304             This is a callback used for stateless session reuse (Session
1305             Tickets, RFC 5077).
1306
1307             This callback will be called as "$sub->($data,[$key_name])" where
1308             $data is the argument given to SSL_ticket_keycb (or undef) and
1309             $key_name depends on the mode:
1310
1311             encrypt ticket
1312                     If a ticket needs to be encrypted the callback will be
1313                     called without $key_name. In this case it should return
1314                     "($current_key,$current_key_name") where $current_key is
1315                     the current key (32 byte random data) and
1316                     $current_key_name the name associated with this key
1317                     (exactly 16 byte). This $current_key_name will be
1318                     incorporated into the ticket.
1319
1320             decrypt ticket
1321                     If a ticket needs to be decrypted the callback will be
1322                     called with $key_name as found in the ticket. It should
1323                     return "($key,$current_key_name") where $key is the key
1324                     associated with the given $key_name and $current_key_name
1325                     the name associated with the currently active key.  If
1326                     $current_key_name is different from the given $key_name
1327                     the callback will be called again to re-encrypt the
1328                     ticket with the currently active key.
1329
1330                     If no key can be found which matches the given $key_name
1331                     then this function should return nothing (empty list).
1332
1333                     This mechanism should be used to limit the life time for
1334                     each key encrypting the ticket. Compromise of a ticket
1335                     encryption key might lead to decryption of SSL sessions
1336                     which used session tickets protected by this key.
1337
1338             Example:
1339
1340                 Net::SSLeay::RAND_bytes(my $oldkey,32);
1341                 Net::SSLeay::RAND_bytes(my $newkey,32);
1342                 my $oldkey_name = pack("a16",'oldsecret');
1343                 my $newkey_name = pack("a16",'newsecret');
1344
1345                 my @keys = (
1346                    [ $newkey_name, $newkey ], # current active key
1347                    [ $oldkey_name, $oldkey ], # already expired
1348                 );
1349
1350                 my $keycb = [ sub {
1351                    my ($mykeys,$name) = @_;
1352
1353                    # return (current_key, current_key_name) if no name given
1354                    return ($mykeys->[0][1],$mykeys->[0][0]) if ! $name;
1355
1356                    # return (matching_key, current_key_name) if we find a key matching
1357                    # the given name
1358                    for(my $i = 0; $i<@$mykeys; $i++) {
1359                        next if $name ne $mykeys->[$i][0];
1360                        return ($mykeys->[$i][1],$mykeys->[0][0]);
1361                    }
1362
1363                    # no matching key found
1364                    return;
1365                 },\@keys ];
1366
1367                 my $srv = IO::Socket::SSL->new(..., SSL_ticket_keycb => $keycb);
1368
1369       accept
1370           This behaves similar to the accept function of the underlying
1371           socket class, but additionally does the initial SSL handshake. But
1372           because the underlying socket class does return a blocking file
1373           handle even when accept is called on a non-blocking socket, the SSL
1374           handshake on the new file object will be done in a blocking way.
1375           Please see the section about non-blocking I/O for details.  If you
1376           don't like this behavior you should do accept on the TCP socket and
1377           then upgrade it with "start_SSL" later.
1378
1379       connect(...)
1380           This behaves similar to the connect function but also does an SSL
1381           handshake.  Because you cannot give SSL specific arguments to this
1382           function, you should better either use "new" to create a connect
1383           SSL socket or "start_SSL" to upgrade an established TCP socket to
1384           SSL.
1385
1386       close(...)
1387           Contrary to a close for a simple INET socket a close in SSL also
1388           mandates a proper shutdown of the SSL part. This is done by sending
1389           a close notify message by both peers.
1390
1391           A naive implementation would thus wait until it receives the close
1392           notify message from the peer - which conflicts with the commonly
1393           expected semantic that a close will not block. The default behavior
1394           is thus to only send a close notify but not  wait for the close
1395           notify of the peer. If this is required "SSL_fast_shutdown" need to
1396           be explicitly set to false.
1397
1398           There are also cases where a SSL shutdown should not be done at
1399           all. This is true for example when forking to let a child deal with
1400           the socket and closing the socket in the parent process. A naive
1401           explicit "close" or an implicit close when destroying the socket in
1402           the parent would send a close notify to the peer which would make
1403           the SSL socket in the client process unusable. In this case an
1404           explicit "close" with "SSL_no_shutdown" set to true should be done
1405           in the parent process.
1406
1407           For more details and other arguments see "stop_SSL" which gets
1408           called from "close" to shutdown the SSL state of the socket.
1409
1410       sysread( BUF, LEN, [ OFFSET ] )
1411           This function behaves from the outside the same as sysread in other
1412           IO::Socket objects, e.g. it returns at most LEN bytes of data.  But
1413           in reality it reads not only LEN bytes from the underlying socket,
1414           but at a single SSL frame. It then returns up to LEN bytes it
1415           decrypted from this SSL frame. If the frame contained more data
1416           than requested it will return only LEN data, buffer the rest and
1417           return it on further read calls.  This means, that it might be
1418           possible to read data, even if the underlying socket is not
1419           readable, so using poll or select might not be sufficient.
1420
1421           sysread will only return data from a single SSL frame, e.g. either
1422           the pending data from the already buffered frame or it will read a
1423           frame from the underlying socket and return the decrypted data. It
1424           will not return data spanning several SSL frames in a single call.
1425
1426           Also, calls to sysread might fail, because it must first finish an
1427           SSL handshake.
1428
1429           To understand these behaviors is essential, if you write
1430           applications which use event loops and/or non-blocking sockets.
1431           Please read the specific sections in this documentation.
1432
1433       syswrite( BUF, [ LEN, [ OFFSET ]] )
1434           This functions behaves from the outside the same as syswrite in
1435           other IO::Socket objects, e.g. it will write at most LEN bytes to
1436           the socket, but there is no guarantee, that all LEN bytes are
1437           written. It will return the number of bytes written.  Because it
1438           basically just calls SSL_write from OpenSSL syswrite will write at
1439           most a single SSL frame. This means, that no more than 16.384
1440           bytes, which is the maximum size of an SSL frame, will be written
1441           at once.
1442
1443           For non-blocking sockets SSL specific behavior applies.  Pease read
1444           the specific section in this documentation.
1445
1446       peek( BUF, LEN, [ OFFSET ])
1447           This function has exactly the same syntax as sysread, and performs
1448           nearly the same task but will not advance the read position so that
1449           successive calls to peek() with the same arguments will return the
1450           same results.  This function requires OpenSSL 0.9.6a or later to
1451           work.
1452
1453       pending()
1454           This function gives you the number of bytes available without
1455           reading from the underlying socket object. This function is
1456           essential if you work with event loops, please see the section
1457           about polling SSL sockets.
1458
1459       get_fingerprint([algo,certificate,pubkey])
1460           This methods returns the fingerprint of the given certificate in
1461           the form "algo$digest_hex", where "algo" is the used algorithm,
1462           default 'sha256'.  If no certificate is given the peer certificate
1463           of the connection is used.  If "pubkey" is true it will not return
1464           the fingerprint of the certificate but instead the fingerprint of
1465           the pubkey inside the certificate as "algo$pub$digest_hex".
1466
1467       get_fingerprint_bin([algo,certificate,pubkey])
1468           This methods returns the binary fingerprint of the given
1469           certificate by using the algorithm "algo", default 'sha256'.  If no
1470           certificate is given the peer certificate of the connection is
1471           used.  If "pubkey" is true it will not return the fingerprint of
1472           the certificate but instead the fingerprint of the pubkey inside
1473           the certificate.
1474
1475       get_cipher()
1476           Returns the string form of the cipher that the IO::Socket::SSL
1477           object is using.
1478
1479       get_sslversion()
1480           Returns the string representation of the SSL version of an
1481           established connection.
1482
1483       get_sslversion_int()
1484           Returns the integer representation of the SSL version of an
1485           established connection.
1486
1487       get_session_reused()
1488           This returns true if the session got reused and false otherwise.
1489           Note that with a reused session no certificates are send within the
1490           handshake and no ciphers are offered and thus functions which rely
1491           on this might not work.
1492
1493       dump_peer_certificate()
1494           Returns a parsable string with select fields from the peer SSL
1495           certificate.  This method directly returns the result of the
1496           dump_peer_certificate() method of Net::SSLeay.
1497
1498       peer_certificate($field;[$refresh])
1499           If a peer certificate exists, this function can retrieve values
1500           from it.  If no field is given the internal representation of
1501           certificate from Net::SSLeay is returned.  If refresh is true it
1502           will not used a cached version, but check again in case the
1503           certificate of the connection has changed due to renegotiation.
1504
1505           The following fields can be queried:
1506
1507           authority (alias issuer)
1508                   The certificate authority which signed the certificate.
1509
1510           owner (alias subject)
1511                   The owner of the certificate.
1512
1513           commonName (alias cn) - only for Net::SSLeay version >=1.30
1514                   The common name, usually the server name for SSL
1515                   certificates.
1516
1517           subjectAltNames - only for Net::SSLeay version >=1.33
1518                   Alternative names for the subject, usually different names
1519                   for the same server, like example.org, example.com,
1520                   *.example.com.
1521
1522                   It returns a list of (typ,value) with typ GEN_DNS,
1523                   GEN_IPADD etc (these constants are exported from
1524                   IO::Socket::SSL).  See
1525                   Net::SSLeay::X509_get_subjectAltNames.
1526
1527       sock_certificate($field)
1528           This is similar to "peer_certificate" but will return the sites own
1529           certificate. The same arguments for $field can be used.  If no
1530           $field is given the certificate handle from the underlying OpenSSL
1531           will be returned. This handle will only be valid as long as the SSL
1532           connection exists and if used afterwards it might result in strange
1533           crashes of the application.
1534
1535       peer_certificates
1536           This returns all the certificates send by the peer, e.g. first the
1537           peers own certificate and then the rest of the chain. You might use
1538           CERT_asHash from IO::Socket::SSL::Utils to inspect each of the
1539           certificates.
1540
1541           This function depends on a version of Net::SSLeay >= 1.58 .
1542
1543       get_servername
1544           This gives the name requested by the client if Server Name
1545           Indication (SNI) was used.
1546
1547       verify_hostname($hostname,$scheme,$publicsuffix)
1548           This verifies the given hostname against the peer certificate using
1549           the given scheme. Hostname is usually what you specify within the
1550           PeerAddr.  See the "SSL_verifycn_publicsuffix" parameter for an
1551           explanation of suffix checking and for the possible values.
1552
1553           Verification of hostname against a certificate is different between
1554           various applications and RFCs. Some scheme allow wildcards for
1555           hostnames, some only in subjectAltNames, and even their different
1556           wildcard schemes are possible.  RFC 6125 provides a good overview.
1557
1558           To ease the verification the following schemes are predefined (both
1559           protocol name and rfcXXXX name can be used):
1560
1561           rfc2818, xmpp (rfc3920), ftp (rfc4217)
1562                   Extended wildcards in subjectAltNames and common name are
1563                   possible, e.g.  *.example.org or even www*.example.org. The
1564                   common name will be only checked if no DNS names are given
1565                   in subjectAltNames.
1566
1567           http (alias www)
1568                   While name checking is defined in rfc2818 the current
1569                   browsers usually accept also an IP address (w/o wildcards)
1570                   within the common name as long as no subjectAltNames are
1571                   defined. Thus this is rfc2818 extended with this feature.
1572
1573           smtp (rfc2595), imap, pop3, acap (rfc4642), netconf (rfc5538),
1574           syslog (rfc5425), snmp (rfc5953)
1575                   Simple wildcards in subjectAltNames are possible, e.g.
1576                   *.example.org matches www.example.org but not
1577                   lala.www.example.org. If nothing from subjectAltNames match
1578                   it checks against the common name, where wildcards are also
1579                   allowed to match the full leftmost label.
1580
1581           ldap (rfc4513)
1582                   Simple wildcards are allowed in subjectAltNames, but not in
1583                   common name.  Common name will be checked even if
1584                   subjectAltNames exist.
1585
1586           sip (rfc5922)
1587                   No wildcards are allowed and common name is checked even if
1588                   subjectAltNames exist.
1589
1590           gist (rfc5971)
1591                   Simple wildcards are allowed in subjectAltNames and common
1592                   name, but common name will only be checked if their are no
1593                   DNS names in subjectAltNames.
1594
1595           default This is a superset of all the rules and is automatically
1596                   used if no scheme is given but a hostname (instead of IP)
1597                   is known.  Extended wildcards are allowed in
1598                   subjectAltNames and common name and common name is checked
1599                   always.
1600
1601           none    No verification will be done.  Actually is does not make
1602                   any sense to call verify_hostname in this case.
1603
1604           The scheme can be given either by specifying the name for one of
1605           the above predefined schemes, or by using a hash which can have the
1606           following keys and values:
1607
1608           check_cn:  0|'always'|'when_only'
1609                   Determines if the common name gets checked. If 'always' it
1610                   will always be checked (like in ldap), if 'when_only' it
1611                   will only be checked if no names are given in
1612                   subjectAltNames (like in http), for any other values the
1613                   common name will not be checked.
1614
1615           wildcards_in_alt: 0|'full_label'|'anywhere'
1616                   Determines if and where wildcards in subjectAltNames are
1617                   possible. If 'full_label' only cases like *.example.org
1618                   will be possible (like in ldap), for 'anywhere'
1619                   www*.example.org is possible too (like http), dangerous
1620                   things like but www.*.org or even '*' will not be allowed.
1621                   For compatibility with older versions 'leftmost' can be
1622                   given instead of 'full_label'.
1623
1624           wildcards_in_cn: 0|'full_label'|'anywhere'
1625                   Similar to wildcards_in_alt, but checks the common name.
1626                   There is no predefined scheme which allows wildcards in
1627                   common names.
1628
1629           ip_in_cn: 0|1|4|6
1630                   Determines if an IP address is allowed in the common name
1631                   (no wildcards are allowed). If set to 4 or 6 it only allows
1632                   IPv4 or IPv6 addresses, any other true value allows both.
1633
1634           callback: \&coderef
1635                   If you give a subroutine for verification it will be called
1636                   with the arguments
1637                   ($hostname,$commonName,@subjectAltNames), where hostname is
1638                   the name given for verification, commonName is the result
1639                   from peer_certificate('cn') and subjectAltNames is the
1640                   result from peer_certificate('subjectAltNames').
1641
1642                   All other arguments for the verification scheme will be
1643                   ignored in this case.
1644
1645       next_proto_negotiated()
1646           This method returns the name of negotiated protocol - e.g.
1647           'http/1.1'. It works for both client and server side of SSL
1648           connection.
1649
1650           NPN support is available with Net::SSLeay 1.46+ and openssl-1.0.1+.
1651           To check support you might call "IO::Socket::SSL->can_npn()".
1652
1653       alpn_selected()
1654           Returns the protocol negotiated via ALPN as a string, e.g.
1655           'http/1.1', 'http/2.0' or 'spdy/3.1'.
1656
1657           ALPN support is available with Net::SSLeay 1.56+ and
1658           openssl-1.0.2+.  To check support, use
1659           "IO::Socket::SSL->can_alpn()".
1660
1661       errstr()
1662           Returns the last error (in string form) that occurred. If you do
1663           not have a real object to perform this method on, call
1664           IO::Socket::SSL::errstr() instead.
1665
1666           For read and write errors on non-blocking sockets, this method may
1667           include the string "SSL wants a read first!" or "SSL wants a write
1668           first!" meaning that the other side is expecting to read from or
1669           write to the socket and wants to be satisfied before you get to do
1670           anything. But with version 0.98 you are better comparing the global
1671           exported variable $SSL_ERROR against the exported symbols
1672           SSL_WANT_READ and SSL_WANT_WRITE.
1673
1674       opened()
1675           This returns false if the socket could not be opened, 1 if the
1676           socket could be opened and the SSL handshake was successful done
1677           and -1 if the underlying IO::Handle is open, but the SSL handshake
1678           failed.
1679
1680       IO::Socket::SSL->start_SSL($socket, ... )
1681           This will convert a glob reference or a socket that you provide to
1682           an IO::Socket::SSL object.   You may also pass parameters to
1683           specify context or connection options as with a call to new().  If
1684           you are using this function on an accept()ed socket, you must set
1685           the parameter "SSL_server" to 1, i.e.
1686           IO::Socket::SSL->start_SSL($socket, SSL_server => 1).  If you have
1687           a class that inherits from IO::Socket::SSL and you want the $socket
1688           to be blessed into your own class instead, use
1689           MyClass->start_SSL($socket) to achieve the desired effect.
1690
1691           Note that if start_SSL() fails in SSL negotiation, $socket will
1692           remain blessed in its original class.    For non-blocking sockets
1693           you better just upgrade the socket to IO::Socket::SSL and call
1694           accept_SSL or connect_SSL and the upgraded object. To just upgrade
1695           the socket set SSL_startHandshake explicitly to 0. If you call
1696           start_SSL w/o this parameter it will revert to blocking behavior
1697           for accept_SSL and connect_SSL.
1698
1699           If given the parameter "Timeout" it will stop if after the timeout
1700           no SSL connection was established. This parameter is only used for
1701           blocking sockets, if it is not given the default Timeout from the
1702           underlying IO::Socket will be used.
1703
1704       stop_SSL(...)
1705           This is the opposite of start_SSL(), connect_SSL() and
1706           accept_SSL(), e.g. it will shutdown the SSL connection and return
1707           to the class before start_SSL(). It gets the same arguments as
1708           close(), in fact close() calls stop_SSL() (but without downgrading
1709           the class).
1710
1711           Will return true if it succeeded and undef if failed. This might be
1712           the case for non-blocking sockets. In this case $! is set to
1713           EWOULDBLOCK and the ssl error to SSL_WANT_READ or SSL_WANT_WRITE.
1714           In this case the call should be retried again with the same
1715           arguments once the socket is ready.
1716
1717           For calling from "stop_SSL" "SSL_fast_shutdown" default to false,
1718           e.g. it waits for the close_notify of the peer. This is necessary
1719           in case you want to downgrade the socket and continue to use it as
1720           a plain socket.
1721
1722           After stop_SSL the socket can again be used to exchange plain data.
1723
1724       connect_SSL, accept_SSL
1725           These functions should be used to do the relevant handshake, if the
1726           socket got created with "new" or upgraded with "start_SSL" and
1727           "SSL_startHandshake" was set to false.  They will return undef
1728           until the handshake succeeded or an error got thrown.  As long as
1729           the function returns undef and $! is set to EWOULDBLOCK one could
1730           retry the call after the socket got readable (SSL_WANT_READ) or
1731           writeable (SSL_WANT_WRITE).
1732
1733       ocsp_resolver
1734           This will create an OCSP resolver object, which can be used to
1735           create OCSP requests for the certificates of the SSL connection.
1736           Which certificates are verified depends on the setting of
1737           "SSL_ocsp_mode": by default only the leaf certificate will be
1738           checked, but with SSL_OCSP_FULL_CHAIN all chain certificates will
1739           be checked.
1740
1741           Because to create an OCSP request the certificate and its issuer
1742           certificate need to be known it is not possible to check
1743           certificates when the trust chain is incomplete or if the
1744           certificate is self-signed.
1745
1746           The OCSP resolver gets created by calling "$ssl->ocsp_resolver" and
1747           provides the following methods:
1748
1749           hard_error
1750                   This returns the hard error when checking the OCSP
1751                   response.  Hard errors are certificate revocations. With
1752                   the "SSL_ocsp_mode" of SSL_OCSP_FAIL_HARD any soft error
1753                   (e.g. failures to get signed information about the
1754                   certificates) will be considered a hard error too.
1755
1756                   The OCSP resolving will stop on the first hard error.
1757
1758                   The method will return undef as long as no hard errors
1759                   occurred and still requests to be resolved. If all requests
1760                   got resolved and no hard errors occurred the method will
1761                   return ''.
1762
1763           soft_error
1764                   This returns the soft error(s) which occurred when asking
1765                   the OCSP responders.
1766
1767           requests
1768                   This will return a hash consisting of
1769                   "(url,request)"-tuples, e.g. which contain the OCSP request
1770                   string and the URL where it should be sent too. The usual
1771                   way to send such a request is as HTTP POST request with a
1772                   content-type of "application/ocsp-request" or as a GET
1773                   request with the base64 and url-encoded request is added to
1774                   the path of the URL.
1775
1776                   After you've handled all these requests and added the
1777                   response with "add_response" you should better call this
1778                   method again to make sure, that no more requests are
1779                   outstanding. IO::Socket::SSL will combine multiple OCSP
1780                   requests for the same server inside a single request, but
1781                   some server don't give a response to all these requests, so
1782                   that one has to ask again with the remaining requests.
1783
1784           add_response($uri,$response)
1785                   This method takes the HTTP body of the response which got
1786                   received when sending the OCSP request to $uri. If no
1787                   response was received or an error occurred one should
1788                   either retry or consider $response as empty which will
1789                   trigger a soft error.
1790
1791                   The method returns the current value of "hard_error", e.g.
1792                   a defined value when no more requests need to be done.
1793
1794           resolve_blocking(%args)
1795                   This combines "requests" and "add_response" which
1796                   HTTP::Tiny to do all necessary requests in a blocking way.
1797                   %args will be given to HTTP::Tiny so that you can put proxy
1798                   settings etc here. HTTP::Tiny will be called with
1799                   "verify_SSL" of false, because the OCSP responses have
1800                   their own signatures so no extra SSL verification is
1801                   needed.
1802
1803                   If you don't want to use blocking requests you need to roll
1804                   your own user agent with "requests" and "add_response".
1805
1806       IO::Socket::SSL->new_from_fd($fd, [mode], %sslargs)
1807           This will convert a socket identified via a file descriptor into an
1808           SSL socket.  Note that the argument list does not include a "MODE"
1809           argument; if you supply one, it will be thoughtfully ignored (for
1810           compatibility with IO::Socket::INET).  Instead, a mode of '+<' is
1811           assumed, and the file descriptor passed must be able to handle such
1812           I/O because the initial SSL handshake requires bidirectional
1813           communication.
1814
1815           Internally the given $fd will be upgraded to a socket object using
1816           the "new_from_fd" method of the super class (IO::Socket::INET or
1817           similar) and then "start_SSL" will be called using the given
1818           %sslargs.  If $fd is already an IO::Socket object you should better
1819           call "start_SSL" directly.
1820
1821       IO::Socket::SSL::default_ca([ path|dir| SSL_ca_file = ..., SSL_ca_path
1822       => ... ])>
1823           Determines or sets the default CA path.  If existing path or dir or
1824           a hash is given it will set the default CA path to this value and
1825           never try to detect it automatically.  If "undef" is given it will
1826           forget any stored defaults and continue with detection of system
1827           defaults.  If no arguments are given it will start detection of
1828           system defaults, unless it has already stored user-set or
1829           previously detected values.
1830
1831           The detection of system defaults works similar to OpenSSL, e.g. it
1832           will check the directory specified in environment variable
1833           SSL_CERT_DIR or the path OPENSSLDIR/certs (SSLCERTS: on VMS) and
1834           the file specified in environment variable SSL_CERT_FILE or the
1835           path OPENSSLDIR/cert.pem (SSLCERTS:cert.pem on VMS). Contrary to
1836           OpenSSL it will check if the SSL_ca_path contains PEM files with
1837           the hash as file name and if the SSL_ca_file looks like PEM.  If no
1838           usable system default can be found it will try to load and use
1839           Mozilla::CA and if not available give up detection.  The result of
1840           the detection will be saved to speed up future calls.
1841
1842           The function returns the saved default CA as hash with SSL_ca_file
1843           and SSL_ca_path.
1844
1845       IO::Socket::SSL::set_default_context(...)
1846           You may use this to make IO::Socket::SSL automatically re-use a
1847           given context (unless specifically overridden in a call to new()).
1848           It accepts one argument, which should be either an IO::Socket::SSL
1849           object or an IO::Socket::SSL::SSL_Context object.  See the
1850           SSL_reuse_ctx option of new() for more details.  Note that this
1851           sets the default context globally, so use with caution (esp. in
1852           mod_perl scripts).
1853
1854       IO::Socket::SSL::set_default_session_cache(...)
1855           You may use this to make IO::Socket::SSL automatically re-use a
1856           given session cache (unless specifically overridden in a call to
1857           new()).  It accepts one argument, which should be an
1858           IO::Socket::SSL::Session_Cache object or similar (e.g. something
1859           which implements get_session, add_session and del_session like
1860           IO::Socket::SSL::Session_Cache does).  See the SSL_session_cache
1861           option of new() for more details.  Note that this sets the default
1862           cache globally, so use with caution.
1863
1864       IO::Socket::SSL::set_defaults(%args)
1865           With this function one can set defaults for all SSL_* parameter
1866           used for creation of the context, like the SSL_verify* parameter.
1867           Any SSL_* parameter can be given or the following short versions:
1868
1869           mode - SSL_verify_mode
1870           callback - SSL_verify_callback
1871           scheme - SSL_verifycn_scheme
1872           name - SSL_verifycn_name
1873       IO::Socket::SSL::set_client_defaults(%args)
1874           Similar to "set_defaults", but only sets the defaults for client
1875           mode.
1876
1877       IO::Socket::SSL::set_server_defaults(%args)
1878           Similar to "set_defaults", but only sets the defaults for server
1879           mode.
1880
1881       IO::Socket::SSL::set_args_filter_hack(\&code|'use_defaults')
1882           Sometimes one has to use code which uses unwanted or invalid
1883           arguments for SSL, typically disabling SSL verification or setting
1884           wrong ciphers or SSL versions.  With this hack it is possible to
1885           override these settings and restore sanity.  Example:
1886
1887               IO::Socket::SSL::set_args_filter_hack( sub {
1888                   my ($is_server,$args) = @_;
1889                   if ( ! $is_server ) {
1890                       # client settings - enable verification with default CA
1891                       # and fallback hostname verification etc
1892                       delete @{$args}{qw(
1893                           SSL_verify_mode
1894                           SSL_ca_file
1895                           SSL_ca_path
1896                           SSL_verifycn_scheme
1897                           SSL_version
1898                       )};
1899                       # and add some fingerprints for known certs which are signed by
1900                       # unknown CAs or are self-signed
1901                       $args->{SSL_fingerprint} = ...
1902                   }
1903               });
1904
1905           With the short setting "set_args_filter_hack('use_defaults')" it
1906           will prefer the default settings in all cases. These default
1907           settings can be modified with "set_defaults", "set_client_defaults"
1908           and "set_server_defaults".
1909
1910       The following methods are unsupported (not to mention futile!) and
1911       IO::Socket::SSL will emit a large CROAK() if you are silly enough to
1912       use them:
1913
1914       truncate
1915       stat
1916       ungetc
1917       setbuf
1918       setvbuf
1919       fdopen
1920       send/recv
1921           Note that send() and recv() cannot be reliably trapped by a tied
1922           filehandle (such as that used by IO::Socket::SSL) and so may send
1923           unencrypted data over the socket.    Object-oriented calls to these
1924           functions will fail, telling you to use the print/printf/syswrite
1925           and read/sysread families instead.
1926

DEPRECATIONS

1928       The following functions are deprecated and are only retained for
1929       compatibility:
1930
1931       context_init()
1932         use the SSL_reuse_ctx option if you want to re-use a context
1933
1934       socketToSSL() and socket_to_SSL()
1935         use IO::Socket::SSL->start_SSL() instead
1936
1937       kill_socket()
1938         use close() instead
1939
1940       get_peer_certificate()
1941         use the peer_certificate() function instead.  Used to return
1942         X509_Certificate with methods subject_name and issuer_name.  Now
1943         simply returns $self which has these methods (although deprecated).
1944
1945       issuer_name()
1946         use peer_certificate( 'issuer' ) instead
1947
1948       subject_name()
1949         use peer_certificate( 'subject' ) instead
1950

EXAMPLES

1952       See the 'example' directory, the tests in 't' and also the tools in
1953       'util'.
1954

BUGS

1956       If you use IO::Socket::SSL together with threads you should load it
1957       (e.g. use or require) inside the main thread before creating any other
1958       threads which use it.  This way it is much faster because it will be
1959       initialized only once. Also there are reports that it might crash the
1960       other way.
1961
1962       Creating an IO::Socket::SSL object in one thread and closing it in
1963       another thread will not work.
1964
1965       IO::Socket::SSL does not work together with
1966       Storable::fd_retrieve/fd_store.  See BUGS file for more information and
1967       how to work around the problem.
1968
1969       Non-blocking and timeouts (which are based on non-blocking) are not
1970       supported on Win32, because the underlying IO::Socket::INET does not
1971       support non-blocking on this platform.
1972
1973       If you have a server and it looks like you have a memory leak you might
1974       check the size of your session cache. Default for Net::SSLeay seems to
1975       be 20480, see the example for SSL_create_ctx_callback for how to limit
1976       it.
1977
1978       TLS 1.3 support regarding session reuse is incomplete.
1979

SEE ALSO

1981       IO::Socket::INET, IO::Socket::INET6, IO::Socket::IP, Net::SSLeay.
1982

THANKS

1984       Many thanks to all who added patches or reported bugs or helped
1985       IO::Socket::SSL another way. Please keep reporting bugs and help with
1986       patches, even if they just fix the documentation.
1987
1988       Special thanks to the team of Net::SSLeay for the good cooperation.
1989

AUTHORS

1991       Steffen Ullrich, <sullr at cpan.org> is the current maintainer.
1992
1993       Peter Behroozi, <behrooz at fas.harvard.edu> (Note the lack of an "i"
1994       at the end of "behrooz")
1995
1996       Marko Asplund, <marko.asplund at kronodoc.fi>, was the original author
1997       of IO::Socket::SSL.
1998
1999       Patches incorporated from various people, see file Changes.
2000
2002       The original versions of this module are Copyright (C) 1999-2002 Marko
2003       Asplund.
2004
2005       The rewrite of this module is Copyright (C) 2002-2005 Peter Behroozi.
2006
2007       Versions 0.98 and newer are Copyright (C) 2006-2014 Steffen Ullrich.
2008
2009       This module is free software; you can redistribute it and/or modify it
2010       under the same terms as Perl itself.
2011
2012
2013
2014perl v5.30.1                      2019-11-25                IO::Socket::SSL(3)
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