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+=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.
+
+=item SSL_OP_NO_TICKET
+
+Normally clients and servers will, where possible, transparently make use
+of RFC4507bis tickets for stateless session resumption if extension support
+is explicitly set when OpenSSL is compiled.
+
+If this option is set this functionality is disabled and tickets will
+not be used by clients or servers.
+
+=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