SSL_CTX_set_options.pod revision 100936
1=pod 2 3=head1 NAME 4 5SSL_CTX_set_options, SSL_set_options, SSL_CTX_get_options, SSL_get_options - manipulate SSL engine options 6 7=head1 SYNOPSIS 8 9 #include <openssl/ssl.h> 10 11 long SSL_CTX_set_options(SSL_CTX *ctx, long options); 12 long SSL_set_options(SSL *ssl, long options); 13 14 long SSL_CTX_get_options(SSL_CTX *ctx); 15 long SSL_get_options(SSL *ssl); 16 17=head1 DESCRIPTION 18 19SSL_CTX_set_options() adds the options set via bitmask in B<options> to B<ctx>. 20Options already set before are not cleared! 21 22SSL_set_options() adds the options set via bitmask in B<options> to B<ssl>. 23Options already set before are not cleared! 24 25SSL_CTX_get_options() returns the options set for B<ctx>. 26 27SSL_get_options() returns the options set for B<ssl>. 28 29=head1 NOTES 30 31The behaviour of the SSL library can be changed by setting several options. 32The options are coded as bitmasks and can be combined by a logical B<or> 33operation (|). Options can only be added but can never be reset. 34 35SSL_CTX_set_options() and SSL_set_options() affect the (external) 36protocol behaviour of the SSL library. The (internal) behaviour of 37the API can be changed by using the similar 38L<SSL_CTX_set_mode(3)|SSL_CTX_set_mode(3)> and SSL_set_mode() functions. 39 40During a handshake, the option settings of the SSL object are used. When 41a new SSL object is created from a context using SSL_new(), the current 42option setting is copied. Changes to B<ctx> do not affect already created 43SSL objects. SSL_clear() does not affect the settings. 44 45The following B<bug workaround> options are available: 46 47=over 4 48 49=item SSL_OP_MICROSOFT_SESS_ID_BUG 50 51www.microsoft.com - when talking SSLv2, if session-id reuse is 52performed, the session-id passed back in the server-finished message 53is different from the one decided upon. 54 55=item SSL_OP_NETSCAPE_CHALLENGE_BUG 56 57Netscape-Commerce/1.12, when talking SSLv2, accepts a 32 byte 58challenge but then appears to only use 16 bytes when generating the 59encryption keys. Using 16 bytes is ok but it should be ok to use 32. 60According to the SSLv3 spec, one should use 32 bytes for the challenge 61when operating in SSLv2/v3 compatibility mode, but as mentioned above, 62this breaks this server so 16 bytes is the way to go. 63 64=item SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG 65 66ssl3.netscape.com:443, first a connection is established with RC4-MD5. 67If it is then resumed, we end up using DES-CBC3-SHA. It should be 68RC4-MD5 according to 7.6.1.3, 'cipher_suite'. 69 70Netscape-Enterprise/2.01 (https://merchant.netscape.com) has this bug. 71It only really shows up when connecting via SSLv2/v3 then reconnecting 72via SSLv3. The cipher list changes.... 73 74NEW INFORMATION. Try connecting with a cipher list of just 75DES-CBC-SHA:RC4-MD5. For some weird reason, each new connection uses 76RC4-MD5, but a re-connect tries to use DES-CBC-SHA. So netscape, when 77doing a re-connect, always takes the first cipher in the cipher list. 78 79=item SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG 80 81... 82 83=item SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER 84 85... 86 87=item SSL_OP_MSIE_SSLV2_RSA_PADDING 88 89... 90 91=item SSL_OP_SSLEAY_080_CLIENT_DH_BUG 92 93... 94 95=item SSL_OP_TLS_D5_BUG 96 97... 98 99=item SSL_OP_TLS_BLOCK_PADDING_BUG 100 101... 102 103=item SSL_OP_TLS_ROLLBACK_BUG 104 105Disable version rollback attack detection. 106 107During the client key exchange, the client must send the same information 108about acceptable SSL/TLS protocol levels as during the first hello. Some 109clients violate this rule by adapting to the server's answer. (Example: 110the client sends a SSLv2 hello and accepts up to SSLv3.1=TLSv1, the server 111only understands up to SSLv3. In this case the client must still use the 112same SSLv3.1=TLSv1 announcement. Some clients step down to SSLv3 with respect 113to the server's answer and violate the version rollback protection.) 114 115=item SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS 116 117Disables a countermeasure against a SSL 3.0/TLS 1.0 protocol 118vulnerability affecting CBC ciphers, which cannot be handled by some 119broken SSL implementations. This option has no effect for connections 120using other ciphers. 121 122=item SSL_OP_ALL 123 124All of the above bug workarounds. 125 126=back 127 128It is usually safe to use B<SSL_OP_ALL> to enable the bug workaround 129options if compatibility with somewhat broken implementations is 130desired. 131 132The following B<modifying> options are available: 133 134=over 4 135 136=item SSL_OP_SINGLE_DH_USE 137 138Always create a new key when using temporary/ephemeral DH parameters 139(see L<SSL_CTX_set_tmp_dh_callback(3)|SSL_CTX_set_tmp_dh_callback(3)>). 140This option must be used to prevent small subgroup attacks, when 141the DH parameters were not generated using "strong" primes 142(e.g. when using DSA-parameters, see L<dhparam(1)|dhparam(1)>). 143If "strong" primes were used, it is not strictly necessary to generate 144a new DH key during each handshake but it is also recommended. 145SSL_OP_SINGLE_DH_USE should therefore be enabled whenever 146temporary/ephemeral DH parameters are used. 147 148=item SSL_OP_EPHEMERAL_RSA 149 150Always use ephemeral (temporary) RSA key when doing RSA operations 151(see L<SSL_CTX_set_tmp_rsa_callback(3)|SSL_CTX_set_tmp_rsa_callback(3)>). 152According to the specifications this is only done, when a RSA key 153can only be used for signature operations (namely under export ciphers 154with restricted RSA keylength). By setting this option, ephemeral 155RSA keys are always used. This option breaks compatibility with the 156SSL/TLS specifications and may lead to interoperability problems with 157clients and should therefore never be used. Ciphers with EDH (ephemeral 158Diffie-Hellman) key exchange should be used instead. 159 160=item SSL_OP_PKCS1_CHECK_1 161 162... 163 164=item SSL_OP_PKCS1_CHECK_2 165 166... 167 168=item SSL_OP_NETSCAPE_CA_DN_BUG 169 170If we accept a netscape connection, demand a client cert, have a 171non-self-sighed CA which does not have it's CA in netscape, and the 172browser has a cert, it will crash/hang. Works for 3.x and 4.xbeta 173 174=item SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG 175 176... 177 178=item SSL_OP_NO_SSLv2 179 180Do not use the SSLv2 protocol. 181 182=item SSL_OP_NO_SSLv3 183 184Do not use the SSLv3 protocol. 185 186=item SSL_OP_NO_TLSv1 187 188Do not use the TLSv1 protocol. 189 190=back 191 192=head1 RETURN VALUES 193 194SSL_CTX_set_options() and SSL_set_options() return the new options bitmask 195after adding B<options>. 196 197SSL_CTX_get_options() and SSL_get_options() return the current bitmask. 198 199=head1 SEE ALSO 200 201L<ssl(3)|ssl(3)>, L<SSL_new(3)|SSL_new(3)>, L<SSL_clear(3)|SSL_clear(3)>, 202L<SSL_CTX_set_tmp_dh_callback(3)|SSL_CTX_set_tmp_dh_callback(3)>, 203L<SSL_CTX_set_tmp_rsa_callback(3)|SSL_CTX_set_tmp_rsa_callback(3)>, 204L<dhparam(1)|dhparam(1)> 205 206=head1 HISTORY 207 208SSL_OP_TLS_ROLLBACK_BUG has been added in OpenSSL 0.9.6. 209 210B<SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS> has been added in OpenSSL 0.9.6e. 211Versions up to OpenSSL 0.9.6c do not include the countermeasure that 212can be disabled with this option (in OpenSSL 0.9.6d, it was always 213enabled). 214 215=cut 216