SSL_CTX_set_options(3)

     SSL_CTX_set_options(3) 0.9.6h (2002-07-10) 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 setting
          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() 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 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

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     SSL_CTX_set_options(3) 0.9.6h (2002-07-10) SSL_CTX_set_options(3)

              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.

          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.

          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_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

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     SSL_CTX_set_options(3) 0.9.6h (2002-07-10) SSL_CTX_set_options(3)

              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_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.

          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_SINGLE_DH_USE
              Always create a new key when using temporary/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 during 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_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.

          SSL_OP_PKCS1_CHECK_1
              ...

          SSL_OP_PKCS1_CHECK_2
              ...

          SSL_OP_NETSCAPE_CA_DN_BUG

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     SSL_CTX_set_options(3) 0.9.6h (2002-07-10) SSL_CTX_set_options(3)

              If we accept a netscape connection, demand a client
              cert, have a non-self-sighed CA which does not have it's
              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.

     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_TLS_ROLLBACK_BUG has been added in OpenSSL 0.9.6.

          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).

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