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 89As of OpenSSL 0.9.7h and 0.9.8a, this option has no effect. 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_DONT_INSERT_EMPTY_FRAGMENTS 104 105Disables a countermeasure against a SSL 3.0/TLS 1.0 protocol 106vulnerability affecting CBC ciphers, which cannot be handled by some 107broken SSL implementations. This option has no effect for connections 108using other ciphers. 109 110=item SSL_OP_ALL 111 112All of the above bug workarounds. 113 114=back 115 116It is usually safe to use B<SSL_OP_ALL> to enable the bug workaround 117options if compatibility with somewhat broken implementations is 118desired. 119 120The following B<modifying> options are available: 121 122=over 4 123 124=item SSL_OP_TLS_ROLLBACK_BUG 125 126Disable version rollback attack detection. 127 128During the client key exchange, the client must send the same information 129about acceptable SSL/TLS protocol levels as during the first hello. Some 130clients violate this rule by adapting to the server's answer. (Example: 131the client sends a SSLv2 hello and accepts up to SSLv3.1=TLSv1, the server 132only understands up to SSLv3. In this case the client must still use the 133same SSLv3.1=TLSv1 announcement. Some clients step down to SSLv3 with respect 134to the server's answer and violate the version rollback protection.) 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. 145B<SSL_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_CIPHER_SERVER_PREFERENCE 161 162When choosing a cipher, use the server's preferences instead of the client 163preferences. When not set, the SSL server will always follow the clients 164preferences. When set, the SSLv3/TLSv1 server will choose following its 165own preferences. Because of the different protocol, for SSLv2 the server 166will send its list of preferences to the client and the client chooses. 167 168=item SSL_OP_PKCS1_CHECK_1 169 170... 171 172=item SSL_OP_PKCS1_CHECK_2 173 174... 175 176=item SSL_OP_NETSCAPE_CA_DN_BUG 177 178If we accept a netscape connection, demand a client cert, have a 179non-self-signed CA which does not have its CA in netscape, and the 180browser has a cert, it will crash/hang. Works for 3.x and 4.xbeta 181 182=item SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG 183 184... 185 186=item SSL_OP_NO_SSLv2 187 188Do not use the SSLv2 protocol. 189 190=item SSL_OP_NO_SSLv3 191 192Do not use the SSLv3 protocol. 193 194=item SSL_OP_NO_TLSv1 195 196Do not use the TLSv1 protocol. 197 198=item SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION 199 200When performing renegotiation as a server, always start a new session 201(i.e., session resumption requests are only accepted in the initial 202handshake). This option is not needed for clients. 203 204=back 205 206=head1 RETURN VALUES 207 208SSL_CTX_set_options() and SSL_set_options() return the new options bitmask 209after adding B<options>. 210 211SSL_CTX_get_options() and SSL_get_options() return the current bitmask. 212 213=head1 SEE ALSO 214 215L<ssl(3)|ssl(3)>, L<SSL_new(3)|SSL_new(3)>, L<SSL_clear(3)|SSL_clear(3)>, 216L<SSL_CTX_set_tmp_dh_callback(3)|SSL_CTX_set_tmp_dh_callback(3)>, 217L<SSL_CTX_set_tmp_rsa_callback(3)|SSL_CTX_set_tmp_rsa_callback(3)>, 218L<dhparam(1)|dhparam(1)> 219 220=head1 HISTORY 221 222B<SSL_OP_CIPHER_SERVER_PREFERENCE> and 223B<SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION> have been added in 224OpenSSL 0.9.7. 225 226B<SSL_OP_TLS_ROLLBACK_BUG> has been added in OpenSSL 0.9.6 and was automatically 227enabled with B<SSL_OP_ALL>. As of 0.9.7, it is no longer included in B<SSL_OP_ALL> 228and must be explicitly set. 229 230B<SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS> has been added in OpenSSL 0.9.6e. 231Versions up to OpenSSL 0.9.6c do not include the countermeasure that 232can be disabled with this option (in OpenSSL 0.9.6d, it was always 233enabled). 234 235=cut 236