=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.
+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.
+Options already set before are not cleared!
SSL_CTX_get_options() returns the options set for B<ctx>.
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.
-During a handshake, the option settings of the SSL object used. When
+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.
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 opperating in SSLv2/v3 compatablity mode, but as mentioned above,
+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
=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_ROLLBACK_BUG
-
-Disable version rollback attack detection.
+=item SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS
-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.)
+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
=back
-It is save and recommended to use SSL_OP_ALL to enable the bug workaround
-options.
+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 DH parameters.
+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
-Also use the temporary RSA key when doing RSA operations.
+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 procotol, for SSLv2 the server
-will send his list of preferences to the client and the client chooses.
+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_NETSCAPE_CA_DN_BUG
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
+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_NON_EXPORT_FIRST
-
-On servers try to use non-export (stronger) ciphers first. This option does
-not work under all circumstances (in the code it is declared "broken").
-
=item SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG
...
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.
+
+=item SSL_OP_NO_TICKET
+
+Normally clients and servers will, where possible, transparently make use
+of RFC4507bis tickets for stateless session resumption.
+
+If this option is set this functionality is disabled and tickets will
+not be used by clients or servers.
+
=back
=head1 RETURN VALUES
=head1 SEE ALSO
-L<ssl(3)|ssl(3)>, L<SSL_new(3)|SSL_new(3)>, L<SSL_clear(3)|SSL_clear(3)>
+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
-SSL_OP_CIPHER_SERVER_PREFERENCE has been added in OpenSSL 0.9.7.
+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.
-SSL_OP_TLS_ROLLBACK_BUG has been added in OpenSSL 0.9.6.
+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