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Diffstat (limited to 'doc/ssl/SSL_CTX_set_options.pod')
-rw-r--r-- | doc/ssl/SSL_CTX_set_options.pod | 235 |
1 files changed, 235 insertions, 0 deletions
diff --git a/doc/ssl/SSL_CTX_set_options.pod b/doc/ssl/SSL_CTX_set_options.pod new file mode 100644 index 0000000..fa63263 --- /dev/null +++ b/doc/ssl/SSL_CTX_set_options.pod @@ -0,0 +1,235 @@ +=pod + +=head1 NAME + +SSL_CTX_set_options, SSL_set_options, SSL_CTX_get_options, SSL_get_options - manipulate SSL engine options + +=head1 SYNOPSIS + + #include <openssl/ssl.h> + + long SSL_CTX_set_options(SSL_CTX *ctx, long options); + long SSL_set_options(SSL *ssl, long options); + + long SSL_CTX_get_options(SSL_CTX *ctx); + long SSL_get_options(SSL *ssl); + +=head1 DESCRIPTION + +SSL_CTX_set_options() adds the options set via bitmask in B<options> to B<ctx>. +Options already set before are not cleared! + +SSL_set_options() adds the options set via bitmask in B<options> to B<ssl>. +Options already set before are not cleared! + +SSL_CTX_get_options() returns the options set for B<ctx>. + +SSL_get_options() returns the options set for B<ssl>. + +=head1 NOTES + +The behaviour of the SSL library can be changed by setting several options. +The options are coded as bitmasks and can be combined by a logical B<or> +operation (|). Options can only be added but can never be reset. + +SSL_CTX_set_options() and SSL_set_options() affect the (external) +protocol behaviour of the SSL library. The (internal) behaviour of +the API can be changed by using the similar +L<SSL_CTX_set_mode(3)|SSL_CTX_set_mode(3)> and SSL_set_mode() functions. + +During a handshake, the option settings of the SSL object are used. When +a new SSL object is created from a context using SSL_new(), the current +option setting is copied. Changes to B<ctx> do not affect already created +SSL objects. SSL_clear() does not affect the settings. + +The following B<bug workaround> options are available: + +=over 4 + +=item SSL_OP_MICROSOFT_SESS_ID_BUG + +www.microsoft.com - when talking SSLv2, if session-id reuse is +performed, the session-id passed back in the server-finished message +is different from the one decided upon. + +=item SSL_OP_NETSCAPE_CHALLENGE_BUG + +Netscape-Commerce/1.12, when talking SSLv2, accepts a 32 byte +challenge but then appears to only use 16 bytes when generating the +encryption keys. Using 16 bytes is ok but it should be ok to use 32. +According to the SSLv3 spec, one should use 32 bytes for the challenge +when operating in SSLv2/v3 compatibility mode, but as mentioned above, +this breaks this server so 16 bytes is the way to go. + +=item SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG + +ssl3.netscape.com:443, first a connection is established with RC4-MD5. +If it is then resumed, we end up using DES-CBC3-SHA. It should be +RC4-MD5 according to 7.6.1.3, 'cipher_suite'. + +Netscape-Enterprise/2.01 (https://merchant.netscape.com) has this bug. +It only really shows up when connecting via SSLv2/v3 then reconnecting +via SSLv3. The cipher list changes.... + +NEW INFORMATION. Try connecting with a cipher list of just +DES-CBC-SHA:RC4-MD5. For some weird reason, each new connection uses +RC4-MD5, but a re-connect tries to use DES-CBC-SHA. So netscape, when +doing a re-connect, always takes the first cipher in the cipher list. + +=item SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG + +... + +=item SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER + +... + +=item SSL_OP_MSIE_SSLV2_RSA_PADDING + +As of OpenSSL 0.9.7h and 0.9.8a, this option has no effect. + +=item SSL_OP_SSLEAY_080_CLIENT_DH_BUG + +... + +=item SSL_OP_TLS_D5_BUG + +... + +=item SSL_OP_TLS_BLOCK_PADDING_BUG + +... + +=item SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS + +Disables a countermeasure against a SSL 3.0/TLS 1.0 protocol +vulnerability affecting CBC ciphers, which cannot be handled by some +broken SSL implementations. This option has no effect for connections +using other ciphers. + +=item SSL_OP_ALL + +All of the above bug workarounds. + +=back + +It is usually safe to use B<SSL_OP_ALL> to enable the bug workaround +options if compatibility with somewhat broken implementations is +desired. + +The following B<modifying> options are available: + +=over 4 + +=item SSL_OP_TLS_ROLLBACK_BUG + +Disable version rollback attack detection. + +During the client key exchange, the client must send the same information +about acceptable SSL/TLS protocol levels as during the first hello. Some +clients violate this rule by adapting to the server's answer. (Example: +the client sends a SSLv2 hello and accepts up to SSLv3.1=TLSv1, the server +only understands up to SSLv3. In this case the client must still use the +same SSLv3.1=TLSv1 announcement. Some clients step down to SSLv3 with respect +to the server's answer and violate the version rollback protection.) + +=item SSL_OP_SINGLE_DH_USE + +Always create a new key when using temporary/ephemeral DH parameters +(see L<SSL_CTX_set_tmp_dh_callback(3)|SSL_CTX_set_tmp_dh_callback(3)>). +This option must be used to prevent small subgroup attacks, when +the DH parameters were not generated using "strong" primes +(e.g. when using DSA-parameters, see L<dhparam(1)|dhparam(1)>). +If "strong" primes were used, it is not strictly necessary to generate +a new DH key during each handshake but it is also recommended. +B<SSL_OP_SINGLE_DH_USE> should therefore be enabled whenever +temporary/ephemeral DH parameters are used. + +=item SSL_OP_EPHEMERAL_RSA + +Always use ephemeral (temporary) RSA key when doing RSA operations +(see L<SSL_CTX_set_tmp_rsa_callback(3)|SSL_CTX_set_tmp_rsa_callback(3)>). +According to the specifications this is only done, when a RSA key +can only be used for signature operations (namely under export ciphers +with restricted RSA keylength). By setting this option, ephemeral +RSA keys are always used. This option breaks compatibility with the +SSL/TLS specifications and may lead to interoperability problems with +clients and should therefore never be used. Ciphers with EDH (ephemeral +Diffie-Hellman) key exchange should be used instead. + +=item SSL_OP_CIPHER_SERVER_PREFERENCE + +When choosing a cipher, use the server's preferences instead of the client +preferences. When not set, the SSL server will always follow the clients +preferences. When set, the SSLv3/TLSv1 server will choose following its +own preferences. Because of the different protocol, for SSLv2 the server +will send its list of preferences to the client and the client chooses. + +=item SSL_OP_PKCS1_CHECK_1 + +... + +=item SSL_OP_PKCS1_CHECK_2 + +... + +=item SSL_OP_NETSCAPE_CA_DN_BUG + +If we accept a netscape connection, demand a client cert, have a +non-self-signed CA which does not have its CA in netscape, and the +browser has a cert, it will crash/hang. Works for 3.x and 4.xbeta + +=item SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG + +... + +=item SSL_OP_NO_SSLv2 + +Do not use the SSLv2 protocol. + +=item SSL_OP_NO_SSLv3 + +Do not use the SSLv3 protocol. + +=item SSL_OP_NO_TLSv1 + +Do not use the TLSv1 protocol. + +=item SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION + +When performing renegotiation as a server, always start a new session +(i.e., session resumption requests are only accepted in the initial +handshake). This option is not needed for clients. + +=back + +=head1 RETURN VALUES + +SSL_CTX_set_options() and SSL_set_options() return the new options bitmask +after adding B<options>. + +SSL_CTX_get_options() and SSL_get_options() return the current bitmask. + +=head1 SEE ALSO + +L<ssl(3)|ssl(3)>, L<SSL_new(3)|SSL_new(3)>, L<SSL_clear(3)|SSL_clear(3)>, +L<SSL_CTX_set_tmp_dh_callback(3)|SSL_CTX_set_tmp_dh_callback(3)>, +L<SSL_CTX_set_tmp_rsa_callback(3)|SSL_CTX_set_tmp_rsa_callback(3)>, +L<dhparam(1)|dhparam(1)> + +=head1 HISTORY + +B<SSL_OP_CIPHER_SERVER_PREFERENCE> and +B<SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION> have been added in +OpenSSL 0.9.7. + +B<SSL_OP_TLS_ROLLBACK_BUG> has been added in OpenSSL 0.9.6 and was automatically +enabled with B<SSL_OP_ALL>. As of 0.9.7, it is no longer included in B<SSL_OP_ALL> +and must be explicitly set. + +B<SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS> has been added in OpenSSL 0.9.6e. +Versions up to OpenSSL 0.9.6c do not include the countermeasure that +can be disabled with this option (in OpenSSL 0.9.6d, it was always +enabled). + +=cut |