diff options
Diffstat (limited to 'crypto/openssl/doc/ssl/SSL_CTX_set_tmp_dh_callback.pod')
| -rw-r--r-- | crypto/openssl/doc/ssl/SSL_CTX_set_tmp_dh_callback.pod | 29 |
1 files changed, 5 insertions, 24 deletions
diff --git a/crypto/openssl/doc/ssl/SSL_CTX_set_tmp_dh_callback.pod b/crypto/openssl/doc/ssl/SSL_CTX_set_tmp_dh_callback.pod index b754c16..234fbc8 100644 --- a/crypto/openssl/doc/ssl/SSL_CTX_set_tmp_dh_callback.pod +++ b/crypto/openssl/doc/ssl/SSL_CTX_set_tmp_dh_callback.pod @@ -48,25 +48,8 @@ even if he gets hold of the normal (certified) key, as this key was only used for signing. In order to perform a DH key exchange the server must use a DH group -(DH parameters) and generate a DH key. -The server will always generate a new DH key during the negotiation -if either the DH parameters are supplied via callback or the -SSL_OP_SINGLE_DH_USE option of SSL_CTX_set_options(3) is set (or both). -It will immediately create a DH key if DH parameters are supplied via -SSL_CTX_set_tmp_dh() and SSL_OP_SINGLE_DH_USE is not set. -In this case, -it may happen that a key is generated on initialization without later -being needed, while on the other hand the computer time during the -negotiation is being saved. - -If "strong" primes were used to generate the DH parameters, it is not strictly -necessary to generate a new key for each handshake but it does improve forward -secrecy. If it is not assured that "strong" primes were used, -SSL_OP_SINGLE_DH_USE must be used in order to prevent small subgroup -attacks. Always using SSL_OP_SINGLE_DH_USE has an impact on the -computer time needed during negotiation, but it is not very large, so -application authors/users should consider always enabling this option. -The option is required to implement perfect forward secrecy (PFS). +(DH parameters) and generate a DH key. The server will always generate +a new DH key during the negotiation. As generating DH parameters is extremely time consuming, an application should not generate the parameters on the fly but supply the parameters. @@ -93,10 +76,9 @@ can supply the DH parameters via a callback function. Previous versions of the callback used B<is_export> and B<keylength> parameters to control parameter generation for export and non-export cipher suites. Modern servers that do not support export ciphersuites -are advised to either use SSL_CTX_set_tmp_dh() in combination with -SSL_OP_SINGLE_DH_USE, or alternatively, use the callback but ignore -B<keylength> and B<is_export> and simply supply at least 2048-bit -parameters in the callback. +are advised to either use SSL_CTX_set_tmp_dh() or alternatively, use +the callback but ignore B<keylength> and B<is_export> and simply +supply at least 2048-bit parameters in the callback. =head1 EXAMPLES @@ -128,7 +110,6 @@ partly left out.) if (SSL_CTX_set_tmp_dh(ctx, dh_2048) != 1) { /* Error. */ } - SSL_CTX_set_options(ctx, SSL_OP_SINGLE_DH_USE); ... =head1 RETURN VALUES |
