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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) pro‐
       tocol 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 per‐
	   formed, 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 chal‐
	   lenge 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 net‐
	   scape, 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 vul‐
	   nerability affecting CBC ciphers, which cannot be handled by some
	   broken SSL implementations.	This option has no effect for connec‐
	   tions 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
	   protection.)

       SSL_OP_SINGLE_DH_USE
	   Always create a new key when using temporary/ephemeral DH parame‐
	   ters (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-parame‐
	   ters, 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 specifica‐
	   tions this is only done, when a RSA key can only be used for signa‐
	   ture 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 specifica‐
	   tions 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 pro‐
	   tocol, 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 ses‐
	   sion (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 bit‐
       mask 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_RESUMP‐
       TION_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 auto‐
       matically 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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