1SSL_CTX_SET_TMP_DH_CALLBACK(3ossl) OpenSSL SSL_CTX_SET_TMP_DH_CALLBACK(3ossl)
2
6 SSL_CTX_set_dh_auto, SSL_set_dh_auto, SSL_CTX_set0_tmp_dh_pkey,
7 SSL_set0_tmp_dh_pkey, SSL_CTX_set_tmp_dh_callback, SSL_CTX_set_tmp_dh,
8 SSL_set_tmp_dh_callback, SSL_set_tmp_dh - handle DH keys for ephemeral
9 key exchange
10
12 #include <openssl/ssl.h>
13 long SSL_CTX_set_dh_auto(SSL_CTX *ctx, int onoff);
15 long SSL_set_dh_auto(SSL *s, int onoff);
16 int SSL_CTX_set0_tmp_dh_pkey(SSL_CTX *ctx, EVP_PKEY *dhpkey);
17 int SSL_set0_tmp_dh_pkey(SSL *s, EVP_PKEY *dhpkey);
18 The following functions have been deprecated since OpenSSL 3.0, and can
20 be hidden entirely by defining OPENSSL_API_COMPAT with a suitable
21 version value, see openssl_user_macros(7):
22 void SSL_CTX_set_tmp_dh_callback(SSL_CTX *ctx,
24 DH *(*tmp_dh_callback)(SSL *ssl, int is_export,
25 int keylength));
26 long SSL_CTX_set_tmp_dh(SSL_CTX *ctx, DH *dh);
27 void SSL_set_tmp_dh_callback(SSL *ctx,
29 DH *(*tmp_dh_callback)(SSL *ssl, int is_export,
30 int keylength));
31 long SSL_set_tmp_dh(SSL *ssl, DH *dh);
32
34 The functions described on this page are relevant for servers only.
35 Some ciphersuites may use ephemeral Diffie-Hellman (DH) key exchange.
37 In these cases, the session data is negotiated using the
38 ephemeral/temporary DH key and the key supplied and certified by the
39 certificate chain is only used for signing. Anonymous ciphers (without
40 a permanent server key) also use ephemeral DH keys.
41 Using ephemeral DH key exchange yields forward secrecy as the
43 connection can only be decrypted when the DH key is known. By
44 generating a temporary DH key inside the server application that is
45 lost when the application is left, it becomes impossible for an
46 attacker to decrypt past sessions, even if they get hold of the normal
47 (certified) key, as this key was only used for signing.
48 In order to perform a DH key exchange the server must use a DH group
50 (DH parameters) and generate a DH key. The server will always generate
51 a new DH key during the negotiation.
52 As generating DH parameters is extremely time consuming, an application
54 should not generate the parameters on the fly. DH parameters can be
55 reused, as the actual key is newly generated during the negotiation.
56 Typically applications should use well know DH parameters that have
58 built-in support in OpenSSL. The macros SSL_CTX_set_dh_auto() and
59 SSL_set_dh_auto() configure OpenSSL to use the default built-in DH
60 parameters for the SSL_CTX and SSL objects respectively. Passing a
61 value of 1 in the onoff parameter switches the feature on, and passing
62 a value of 0 switches it off. The default setting is off.
63 If "auto" DH parameters are switched on then the parameters will be
65 selected to be consistent with the size of the key associated with the
66 server's certificate. If there is no certificate (e.g. for PSK
67 ciphersuites), then it it will be consistent with the size of the
68 negotiated symmetric cipher key.
69 Applications may supply their own DH parameters instead of using the
71 built-in values. This approach is discouraged and applications should
72 in preference use the built-in parameter support described above.
73 Applications wishing to supply their own DH parameters should call
74 SSL_CTX_set0_tmp_dh_pkey() or SSL_set0_tmp_dh_pkey() to supply the
75 parameters for the SSL_CTX or SSL respectively. The parameters should
76 be supplied in the dhpkey argument as an EVP_PKEY containing DH
77 parameters. Ownership of the dhpkey value is passed to the SSL_CTX or
78 SSL object as a result of this call, and so the caller should not free
79 it if the function call is successful.
80 The deprecated macros SSL_CTX_set_tmp_dh() and SSL_set_tmp_dh() do the
82 same thing as SSL_CTX_set0_tmp_dh_pkey() and SSL_set0_tmp_dh_pkey()
83 except that the DH parameters are supplied in a DH object instead in
84 the dh argument, and ownership of the DH object is retained by the
85 application. Applications should use "auto" parameters instead, or call
86 SSL_CTX_set0_tmp_dh_pkey() or SSL_set0_tmp_dh_pkey() as appropriate.
87 An application may instead specify the DH parameters via a callback
89 function using the functions SSL_CTX_set_tmp_dh_callback() or
90 SSL_set_tmp_dh_callback() to set the callback for the SSL_CTX or SSL
91 object respectively. These functions are deprecated. Applications
92 should instead use "auto" parameters, or specify the parameters via
93 SSL_CTX_set0_tmp_dh_pkey() or SSL_set0_tmp_dh_pkey() as appropriate.
94 The callback will be invoked during a connection when DH parameters are
96 required. The SSL object for the current connection is supplied as an
97 argument. Previous versions of OpenSSL used the is_export and keylength
98 arguments to control parameter generation for export and non-export
99 cipher suites. Modern OpenSSL does not support export ciphersuites and
100 so these arguments are unused and can be ignored by the callback. The
101 callback should return the parameters to be used in a DH object.
102 Ownership of the DH object is retained by the application and should
103 later be freed.
104
106 All of these functions/macros return 1 for success or 0 on error.
107
109 ssl(7), SSL_CTX_set_cipher_list(3), SSL_CTX_set_options(3),
110 openssl-ciphers(1), openssl-dhparam(1)
111
113 Copyright 2001-2022 The OpenSSL Project Authors. All Rights Reserved.
114 Licensed under the Apache License 2.0 (the "License"). You may not use
116 this file except in compliance with the License. You can obtain a copy
117 in the file LICENSE in the source distribution or at
118 <https://www.openssl.org/source/license.html>.
1193.1.1 2023-08-31SSL_CTX_SET_TMP_DH_CALLBACK(3ossl)