SSL_CTX_set_options(3)      OpenSSL      SSL_CTX_set_options(3)





NAME
       SSL_CTX_set_options, SSL_set_options,
       SSL_CTX_get_options, SSL_get_options - manipulate SSL
       engine options

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);

DESCRIPTION
       SSL_CTX_set_options() adds the options set via bitmask
       in options to ctx.  Options already set before are not
       cleared!

       SSL_set_options() adds the options set via bitmask in
       options to ssl.  Options already set before are not
       cleared!

       SSL_CTX_get_options() returns the options set for ctx.

       SSL_get_options() returns the options set for ssl.

NOTES
       The behaviour of the SSL library can be changed by set-
       ting several options.  The options are coded as bitmasks
       and can be combined by a logical 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 SSL_CTX_set_mode(3) and SSL_set_mode() func-
       tions.

       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 ctx do not affect already created SSL
       objects. SSL_clear() does not affect the settings.

       The following bug workaround options are available:

       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.

       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.  Accord-
           ing to the SSLv3 spec, one should use 32 bytes for
           the challenge when operating in SSLv2/v3 compatibil-
           ity mode, but as mentioned above, this breaks this
           server so 16 bytes is the way to go.

       SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG
           ssl3.netscape.com:443, first a connection is estab-
           lished with RC4-MD5.  If it is then resumed, we end
           up using DES-CBC3-SHA.  It should be RC4-MD5 accord-
           ing to 7.6.1.3, 'cipher_suite'.

           Netscape-Enterprise/2.01 (https://mer-
           chant.netscape.com) has this bug.  It only really
           shows up when connecting via SSLv2/v3 then recon-
           necting 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.

       SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG
           ...

       SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER
           ...

       SSL_OP_MSIE_SSLV2_RSA_PADDING
           ...

       SSL_OP_SSLEAY_080_CLIENT_DH_BUG
           ...

       SSL_OP_TLS_D5_BUG
           ...

       SSL_OP_TLS_BLOCK_PADDING_BUG
           ...

       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 implementa-
           tions.  This option has no effect for connections
           using other ciphers.

       SSL_OP_ALL
           All of the above bug workarounds.

       It is usually safe to use SSL_OP_ALL to enable the bug
       workaround options if compatibility with somewhat broken
       implementations is desired.

       The following modifying options are available:

       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 proto-
           col 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 under-
           stands 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.)

       SSL_OP_SINGLE_DH_USE
           Always create a new key when using tempo-
           rary/ephemeral DH parameters (see
           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
           dhparam(1)).  If "strong" primes were used, it is
           not strictly necessary to generate a new DH key dur-
           ing each handshake but it is also recommended.
           SSL_OP_SINGLE_DH_USE should therefore be enabled
           whenever temporary/ephemeral DH parameters are used.

       SSL_OP_EPHEMERAL_RSA
           Always use ephemeral (temporary) RSA key when doing
           RSA operations (see SSL_CTX_set_tmp_rsa_call-
           back(3)).  According to the specifications this is
           only done, when a RSA key can only be used for sig-
           nature 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.

       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 prefer-
           ences. When set, the SSLv3/TLSv1 server will choose
           following its own preferences. Because of the dif-
           ferent protocol, for SSLv2 the server will send his
           list of preferences to the client and the client
           chooses.

       SSL_OP_PKCS1_CHECK_1
           ...

       SSL_OP_PKCS1_CHECK_2
           ...

       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

       SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG
           ...

       SSL_OP_NO_SSLv2
           Do not use the SSLv2 protocol.

       SSL_OP_NO_SSLv3
           Do not use the SSLv3 protocol.

       SSL_OP_NO_TLSv1
           Do not use the TLSv1 protocol.

       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 hand-
           shake).  This option is not needed for clients.

RETURN VALUES
       SSL_CTX_set_options() and SSL_set_options() return the
       new options bitmask after adding options.

       SSL_CTX_get_options() and SSL_get_options() return the
       current bitmask.

SEE ALSO
       ssl(3), SSL_new(3), SSL_clear(3),
       SSL_CTX_set_tmp_dh_callback(3),
       SSL_CTX_set_tmp_rsa_callback(3), dhparam(1)

HISTORY
       SSL_OP_CIPHER_SERVER_PREFERENCE and SSL_OP_NO_SES-
       SION_RESUMPTION_ON_RENEGOTIATION have been added in
       OpenSSL 0.9.7.

       SSL_OP_TLS_ROLLBACK_BUG has been added in OpenSSL 0.9.6
       and was automatically enabled with SSL_OP_ALL. As of
       0.9.7, it is no longer included in SSL_OP_ALL and must
       be explicitly set.

       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).



0.9.7c                     2003-03-20    SSL_CTX_set_options(3)
