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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 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 set-
       tings.

       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.  According to the SSLv3 spec, one should use 32
	   bytes for the challenge when operating in SSLv2/v3 compatibility mode, but as men-
	   tioned 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_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_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 protec-
	   tion.)

       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 rec-
	   ommended.  SSL_OP_SINGLE_DH_USE should therefore be enabled whenever tempo-
	   rary/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_CIPHER_SERVER_PREFERENCE
	   When choosing a cipher, use the server's preferences instead of the client prefer-
	   ences. 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 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 handshake).  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_SESSION_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).

0.9.7d					    2003-11-20			   SSL_CTX_set_options(3)
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