1Mail::DKIM::Signer(3) User Contributed Perl DocumentationMail::DKIM::Signer(3)
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3
4

NAME

6       Mail::DKIM::Signer - generates a DKIM signature for a message
7

SYNOPSIS

9         use Mail::DKIM::Signer;
10         use Mail::DKIM::TextWrap;  #recommended
11
12         # create a signer object
13         my $dkim = Mail::DKIM::Signer->new(
14                         Algorithm => 'rsa-sha1',
15                         Method => 'relaxed',
16                         Domain => 'example.org',
17                         Selector => 'selector1',
18                         KeyFile => 'private.key',
19                         Headers => 'x-header:x-header2',
20                    );
21
22         # read an email from a file handle
23         $dkim->load(*STDIN);
24
25         # or read an email and pass it into the signer, one line at a time
26         while (<STDIN>)
27         {
28             # remove local line terminators
29             chomp;
30             s/\015$//;
31
32             # use SMTP line terminators
33             $dkim->PRINT("$_\015\012");
34         }
35         $dkim->CLOSE;
36
37         # what is the signature result?
38         my $signature = $dkim->signature;
39         print $signature->as_string;
40

DESCRIPTION

42       This class is the part of Mail::DKIM responsible for generating
43       signatures for a given message. You create an object of this class,
44       specifying the parameters of the signature you wish to create, or
45       specifying a callback function so that the signature parameters can be
46       determined later. Next, you feed it the entire message using "PRINT()",
47       completing with "CLOSE()". Finally, use the "signatures()" method to
48       access the generated signatures.
49
50   Pretty Signatures
51       Mail::DKIM includes a signature-wrapping module (which inserts
52       linebreaks into the generated signature so that it looks nicer in the
53       resulting message. To enable this module, simply call
54
55         use Mail::DKIM::TextWrap;
56
57       in your program before generating the signature.
58

CONSTRUCTOR

60   new()
61       Construct an object-oriented signer.
62
63         # create a signer using the default policy
64         my $dkim = Mail::DKIM::Signer->new(
65                         Algorithm => 'rsa-sha1',
66                         Method => 'relaxed',
67                         Domain => 'example.org',
68                         Selector => 'selector1',
69                         KeyFile => 'private.key',
70                         Headers => 'x-header:x-header2',
71                    );
72
73         # create a signer using a custom policy
74         my $dkim = Mail::DKIM::Signer->new(
75                         Policy => $policyfn,
76                    );
77
78       The "default policy" is to create a DKIM signature using the specified
79       parameters, but only if the message's sender matches the domain.  The
80       following parameters can be passed to this new() method to influence
81       the resulting signature: Algorithm, Method, Domain, Selector, KeyFile,
82       Identity, Timestamp.
83
84       If you want different behavior, you can provide a "signer policy"
85       instead. A signer policy is a subroutine or class that determines
86       signature parameters after the message's headers have been parsed.  See
87       the section "SIGNER POLICIES" below for more information.
88
89       See Mail::DKIM::SignerPolicy for more information about policy objects.
90
91       In addition to the parameters demonstrated above, the following are
92       recognized:
93
94       Key rather than using "KeyFile", use "Key" to use an already-loaded
95           Mail::DKIM::PrivateKey object.
96
97       Headers
98           A colon separated list of headers to sign, this is added to the
99           list of default headers as shown in in the DKIM specification.
100
101           For each specified header all headers of that type which are
102           present in the message will be signed, but we will not oversign or
103           sign headers which are not present.
104
105           If you require greater control over signed headers please use the
106           extended_headers() method instead.
107
108           The list of headers signed by default is as follows
109
110               From Sender Reply-To Subject Date
111               Message-ID To Cc MIME-Version
112               Content-Type Content-Transfer-Encoding Content-ID Content-Description
113               Resent-Date Resent-From Resent-Sender Resent-To Resent-cc
114               Resent-Message-ID
115               In-Reply-To References
116               List-Id List-Help List-Unsubscribe List-Subscribe
117               List-Post List-Owner List-Archive
118

METHODS

120   PRINT()
121       Feed part of the message to the signer.
122
123         $dkim->PRINT("a line of the message\015\012");
124
125       Feeds content of the message being signed into the signer.  The API is
126       designed this way so that the entire message does NOT need to be read
127       into memory at once.
128
129       Please note that although the PRINT() method expects you to use SMTP-
130       style line termination characters, you should NOT use the SMTP-style
131       dot-stuffing technique described in RFC 2821 section 4.5.2.  Nor should
132       you use a <CR><LF>.<CR><LF> sequence to terminate the message.
133
134   CLOSE()
135       Call this when finished feeding in the message.
136
137         $dkim->CLOSE;
138
139       This method finishes the canonicalization process, computes a hash, and
140       generates a signature.
141
142   extended_headers()
143       This method overrides the headers to be signed and allows more control
144       than is possible with the Headers property in the constructor.
145
146       The method expects a HashRef to be passed in.
147
148       The Keys are the headers to sign, and the values are either the number
149       of headers of that type to sign, or the special values '*' and '+'.
150
151       * will sign ALL headers of that type present in the message.
152
153       + will sign ALL + 1 headers of that type present in the message to
154       prevent additional headers being added.
155
156       You may override any of the default headers by including them in the
157       hashref, and disable them by giving them a 0 value.
158
159       Keys are case insensitive with the values being added upto the highest
160       value.
161
162           Headers => {
163               'X-test'  => '*',
164               'x-test'  => '1',
165               'Subject' => '+',
166               'Sender'  => 0,
167           },
168
169   add_signature()
170       Used by signer policy to create a new signature.
171
172         $dkim->add_signature(new Mail::DKIM::Signature(...));
173
174       Signer policies can use this method to specify complete parameters for
175       the signature to add, including what type of signature. For more
176       information, see Mail::DKIM::SignerPolicy.
177
178   algorithm()
179       Get or set the selected algorithm.
180
181         $alg = $dkim->algorithm;
182
183         $dkim->algorithm('rsa-sha1');
184
185   domain()
186       Get or set the selected domain.
187
188         $alg = $dkim->domain;
189
190         $dkim->domain('example.org');
191
192   load()
193       Load the entire message from a file handle.
194
195         $dkim->load($file_handle);
196
197       Reads a complete message from the designated file handle, feeding it
198       into the signer.  The message must use <CRLF> line terminators (same as
199       the SMTP protocol).
200
201   headers()
202       Determine which headers to put in signature.
203
204         my $headers = $dkim->headers;
205
206       This is a string containing the names of the header fields that will be
207       signed, separated by colons.
208
209   key()
210       Get or set the private key object.
211
212         my $key = $dkim->key;
213
214         $dkim->key(Mail::DKIM::PrivateKey->load(File => 'private.key'));
215
216       The key object can be any object that implements the sign_digest()
217       method.  (Providing your own object can be useful if your actual keys
218       are stored out-of-process.)
219
220       If you use this method to specify a private key, do not use
221       "key_file()".
222
223   key_file()
224       Get or set the filename containing the private key.
225
226         my $filename = $dkim->key_file;
227
228         $dkim->key_file('private.key');
229
230       If you use this method to specify a private key file, do not use
231       "key()".
232
233   method()
234       Get or set the selected canonicalization method.
235
236         $alg = $dkim->method;
237
238         $dkim->method('relaxed');
239
240   message_originator()
241       Access the "From" header.
242
243         my $address = $dkim->message_originator;
244
245       Returns the "originator address" found in the message, as a
246       Mail::Address object.  This is typically the (first) name and email
247       address found in the From: header. If there is no From: header, then an
248       empty Mail::Address object is returned.
249
250       To get just the email address part, do:
251
252         my $email = $dkim->message_originator->address;
253
254       See also "message_sender()".
255
256   message_sender()
257       Access the "From" or "Sender" header.
258
259         my $address = $dkim->message_sender;
260
261       Returns the "sender" found in the message, as a Mail::Address object.
262       This is typically the (first) name and email address found in the
263       Sender: header. If there is no Sender: header, it is the first name and
264       email address in the From: header. If neither header is present, then
265       an empty Mail::Address object is returned.
266
267       To get just the email address part, do:
268
269         my $email = $dkim->message_sender->address;
270
271       The "sender" is the mailbox of the agent responsible for the actual
272       transmission of the message. For example, if a secretary were to send a
273       message for another person, the "sender" would be the secretary and the
274       "originator" would be the actual author.
275
276   selector()
277       Get or set the current key selector.
278
279         $alg = $dkim->selector;
280
281         $dkim->selector('alpha');
282
283   signature()
284       Access the generated signature object.
285
286         my $signature = $dkim->signature;
287
288       Returns the generated signature. The signature is an object of type
289       Mail::DKIM::Signature. If multiple signatures were generated, this
290       method returns the last one.
291
292       The signature (as text) should be prepended to the message to make the
293       resulting message. At the very least, it should precede any headers
294       that were signed.
295
296   signatures()
297       Access list of generated signature objects.
298
299         my @signatures = $dkim->signatures;
300
301       Returns all generated signatures, as a list.
302

SIGNER POLICIES

304       The new() constructor takes an optional Policy argument. This can be a
305       Perl object or class with an apply() method, or just a simple
306       subroutine reference. The method/subroutine will be called with the
307       signer object as an argument. The policy is responsible for checking
308       the message and specifying signature parameters. The policy must return
309       a nonzero value to create the signature, otherwise no signature will be
310       created. E.g.,
311
312         my $policyfn = sub {
313             my $dkim = shift;
314
315             # specify signature parameters
316             $dkim->algorithm('rsa-sha1');
317             $dkim->method('relaxed');
318             $dkim->domain('example.org');
319             $dkim->selector('mx1');
320
321             # return true value to create the signature
322             return 1;
323         };
324
325       Or the policy object can actually create the signature, using the
326       add_signature method within the policy object.  If you add a signature,
327       you do not need to return a nonzero value.  This mechanism can be
328       utilized to create multiple signatures, or to create the older
329       DomainKey-style signatures.
330
331         my $policyfn = sub {
332             my $dkim = shift;
333             $dkim->add_signature(
334                     new Mail::DKIM::Signature(
335                             Algorithm => 'rsa-sha1',
336                             Method => 'relaxed',
337                             Headers => $dkim->headers,
338                             Domain => 'example.org',
339                             Selector => 'mx1',
340                     ));
341             $dkim->add_signature(
342                     new Mail::DKIM::DkSignature(
343                             Algorithm => 'rsa-sha1',
344                             Method => 'nofws',
345                             Headers => $dkim->headers,
346                             Domain => 'example.org',
347                             Selector => 'mx1',
348                     ));
349             return;
350         };
351
352       If no policy is specified, the default policy is used. The default
353       policy signs every message using the domain, algorithm, method, and
354       selector specified in the new() constructor.
355

SEE ALSO

357       Mail::DKIM::SignerPolicy
358

AUTHOR

360       Jason Long, <jlong@messiah.edu>
361

COPYRIGHT AND LICENSE

363       Copyright (C) 2006-2007 by Messiah College
364
365       This library is free software; you can redistribute it and/or modify it
366       under the same terms as Perl itself, either Perl version 5.8.6 or, at
367       your option, any later version of Perl 5 you may have available.
368
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370
371perl v5.26.3                      2018-10-13             Mail::DKIM::Signer(3)