SSL_CTX_set_options 3 2008-05-09 0.9.9-dev OpenSSL

NAME

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

LIBRARY

libcrypto, -lcrypto

SYNOPSIS


 #include 


 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

_S_S_L___C_T_X___s_e_t___o_p_t_i_o_n_s_(_) adds the options set via bitmask in ooppttiioonnss to ccttxx. Options already set before are not cleared!

_S_S_L___s_e_t___o_p_t_i_o_n_s_(_) adds the options set via bitmask in ooppttiioonnss to ssssll. Options already set before are not cleared!

_S_S_L___C_T_X___g_e_t___o_p_t_i_o_n_s_(_) returns the options set for ccttxx.

_S_S_L___g_e_t___o_p_t_i_o_n_s_(_) returns the options set for ssssll.

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 oorr operation (|). Options can only be added but can never be reset.

_S_S_L___C_T_X___s_e_t___o_p_t_i_o_n_s_(_) and _S_S_L___s_e_t___o_p_t_i_o_n_s_(_) affect the (external) protocol behaviour of the SSL library. The (internal) behaviour of the API can be changed by using the similar _S_S_L___C_T_X___s_e_t___m_o_d_e(3) and _S_S_L___s_e_t___m_o_d_e_(_) functions.

During a handshake, the option settings of the SSL object are used. When a new SSL object is created from a context using _S_S_L___n_e_w_(_), the current option setting is copied. Changes to ccttxx do not affect already created SSL objects. _S_S_L___c_l_e_a_r_(_) does not affect the settings.

The following bbuugg wwoorrkkaarroouunndd 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. 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 As of OpenSSL 0.9.7h and 0.9.8a, this option has no effect.
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 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 SSSSLL__OOPP__AALLLL to enable the bug workaround options if compatibility with somewhat broken implementations is desired.

The following mmooddiiffyyiinngg 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 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.)
SSL_OP_SINGLE_DH_USE Always create a new key when using temporary/ephemeral DH parameters
(see _S_S_L___C_T_X___s_e_t___t_m_p___d_h___c_a_l_l_b_a_c_k(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 _o_p_e_n_s_s_l___d_h_p_a_r_a_m(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. SSSSLL__OOPP__SSIINNGGLLEE__DDHH__UUSSEE 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 _S_S_L___C_T_X___s_e_t___t_m_p___r_s_a___c_a_l_l_b_a_c_k(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_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.
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 handshake). This option is not needed for clients.
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.

RETURN VALUES

_S_S_L___C_T_X___s_e_t___o_p_t_i_o_n_s_(_) and _S_S_L___s_e_t___o_p_t_i_o_n_s_(_) return the new options bitmask after adding ooppttiioonnss.

_S_S_L___C_T_X___g_e_t___o_p_t_i_o_n_s_(_) and _S_S_L___g_e_t___o_p_t_i_o_n_s_(_) return the current bitmask.

SEE ALSO

_s_s_l(3), _S_S_L___n_e_w(3), _S_S_L___c_l_e_a_r(3), _S_S_L___C_T_X___s_e_t___t_m_p___d_h___c_a_l_l_b_a_c_k(3), _S_S_L___C_T_X___s_e_t___t_m_p___r_s_a___c_a_l_l_b_a_c_k(3), _o_p_e_n_s_s_l___d_h_p_a_r_a_m(1)

HISTORY

SSSSLL__OOPP__CCIIPPHHEERR__SSEERRVVEERR__PPRREEFFEERREENNCCEE and SSSSLL__OOPP__NNOO__SSEESSSSIIOONN__RREESSUUMMPPTTIIOONN__OONN__RREENNEEGGOOTTIIAATTIIOONN have been added in OpenSSL 0.9.7.

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

SSSSLL__OOPP__DDOONNTT__IINNSSEERRTT__EEMMPPTTYY__FFRRAAGGMMEENNTTSS 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).