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.\" ========================================================================
.\"
.IX Title "SSL_CTX_set_options 3"
.TH SSL_CTX_set_options 3 "2008-09-06" "0.9.8h" "OpenSSL"
.SH "NAME"
SSL_CTX_set_options, SSL_set_options, SSL_CTX_get_options, SSL_get_options \- manipulate SSL engine options
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/ssl.h>
.Ve
.PP
.Vb 2
\& long SSL_CTX_set_options(SSL_CTX *ctx, long options);
\& long SSL_set_options(SSL *ssl, long options);
.Ve
.PP
.Vb 2
\& long SSL_CTX_get_options(SSL_CTX *ctx);
\& long SSL_get_options(SSL *ssl);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fISSL_CTX_set_options()\fR adds the options set via bitmask in \fBoptions\fR to \fBctx\fR.
Options already set before are not cleared!
.PP
\&\fISSL_set_options()\fR adds the options set via bitmask in \fBoptions\fR to \fBssl\fR.
Options already set before are not cleared!
.PP
\&\fISSL_CTX_get_options()\fR returns the options set for \fBctx\fR.
.PP
\&\fISSL_get_options()\fR returns the options set for \fBssl\fR.
.SH "NOTES"
.IX Header "NOTES"
The behaviour of the \s-1SSL\s0 library can be changed by setting several options.
The options are coded as bitmasks and can be combined by a logical \fBor\fR
operation (|). Options can only be added but can never be reset.
.PP
\&\fISSL_CTX_set_options()\fR and \fISSL_set_options()\fR affect the (external)
protocol behaviour of the \s-1SSL\s0 library. The (internal) behaviour of
the \s-1API\s0 can be changed by using the similar
\&\fISSL_CTX_set_mode\fR\|(3) and \fISSL_set_mode()\fR functions.
.PP
During a handshake, the option settings of the \s-1SSL\s0 object are used. When
a new \s-1SSL\s0 object is created from a context using \fISSL_new()\fR, the current
option setting is copied. Changes to \fBctx\fR do not affect already created
\&\s-1SSL\s0 objects. \fISSL_clear()\fR does not affect the settings.
.PP
The following \fBbug workaround\fR options are available:
.IP "\s-1SSL_OP_MICROSOFT_SESS_ID_BUG\s0" 4
.IX 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.
.IP "\s-1SSL_OP_NETSCAPE_CHALLENGE_BUG\s0" 4
.IX 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.
.IP "\s-1SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG\s0" 4
.IX Item "SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG"
ssl3.netscape.com:443, first a connection is established with \s-1RC4\-MD5\s0.
If it is then resumed, we end up using \s-1DES\-CBC3\-SHA\s0.  It should be
\&\s-1RC4\-MD5\s0 according to 7.6.1.3, 'cipher_suite'.
.Sp
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....
.Sp
\&\s-1NEW\s0 \s-1INFORMATION\s0.  Try connecting with a cipher list of just
\&\s-1DES\-CBC\-SHA:RC4\-MD5\s0.  For some weird reason, each new connection uses
\&\s-1RC4\-MD5\s0, but a re-connect tries to use \s-1DES\-CBC\-SHA\s0.  So netscape, when
doing a re\-connect, always takes the first cipher in the cipher list.
.IP "\s-1SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG\s0" 4
.IX Item "SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG"
\&...
.IP "\s-1SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER\s0" 4
.IX Item "SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER"
\&...
.IP "\s-1SSL_OP_MSIE_SSLV2_RSA_PADDING\s0" 4
.IX Item "SSL_OP_MSIE_SSLV2_RSA_PADDING"
As of OpenSSL 0.9.7h and 0.9.8a, this option has no effect.
.IP "\s-1SSL_OP_SSLEAY_080_CLIENT_DH_BUG\s0" 4
.IX Item "SSL_OP_SSLEAY_080_CLIENT_DH_BUG"
\&...
.IP "\s-1SSL_OP_TLS_D5_BUG\s0" 4
.IX Item "SSL_OP_TLS_D5_BUG"
\&...
.IP "\s-1SSL_OP_TLS_BLOCK_PADDING_BUG\s0" 4
.IX Item "SSL_OP_TLS_BLOCK_PADDING_BUG"
\&...
.IP "\s-1SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS\s0" 4
.IX Item "SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS"
Disables a countermeasure against a \s-1SSL\s0 3.0/TLS 1.0 protocol
vulnerability affecting \s-1CBC\s0 ciphers, which cannot be handled by some
broken \s-1SSL\s0 implementations.  This option has no effect for connections
using other ciphers.
.IP "\s-1SSL_OP_ALL\s0" 4
.IX Item "SSL_OP_ALL"
All of the above bug workarounds.
.PP
It is usually safe to use \fB\s-1SSL_OP_ALL\s0\fR to enable the bug workaround
options if compatibility with somewhat broken implementations is
desired.
.PP
The following \fBmodifying\fR options are available:
.IP "\s-1SSL_OP_TLS_ROLLBACK_BUG\s0" 4
.IX Item "SSL_OP_TLS_ROLLBACK_BUG"
Disable version rollback attack detection.
.Sp
During the client key exchange, the client must send the same information
about acceptable \s-1SSL/TLS\s0 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.)
.IP "\s-1SSL_OP_SINGLE_DH_USE\s0" 4
.IX Item "SSL_OP_SINGLE_DH_USE"
Always create a new key when using temporary/ephemeral \s-1DH\s0 parameters
(see \fISSL_CTX_set_tmp_dh_callback\fR\|(3)).
This option must be used to prevent small subgroup attacks, when
the \s-1DH\s0 parameters were not generated using \*(L"strong\*(R" primes
(e.g. when using DSA\-parameters, see \fIdhparam\fR\|(1)).
If \*(L"strong\*(R" primes were used, it is not strictly necessary to generate
a new \s-1DH\s0 key during each handshake but it is also recommended.
\&\fB\s-1SSL_OP_SINGLE_DH_USE\s0\fR should therefore be enabled whenever
temporary/ephemeral \s-1DH\s0 parameters are used.
.IP "\s-1SSL_OP_EPHEMERAL_RSA\s0" 4
.IX Item "SSL_OP_EPHEMERAL_RSA"
Always use ephemeral (temporary) \s-1RSA\s0 key when doing \s-1RSA\s0 operations
(see \fISSL_CTX_set_tmp_rsa_callback\fR\|(3)).
According to the specifications this is only done, when a \s-1RSA\s0 key
can only be used for signature operations (namely under export ciphers
with restricted \s-1RSA\s0 keylength). By setting this option, ephemeral
\&\s-1RSA\s0 keys are always used. This option breaks compatibility with the
\&\s-1SSL/TLS\s0 specifications and may lead to interoperability problems with
clients and should therefore never be used. Ciphers with \s-1EDH\s0 (ephemeral
Diffie\-Hellman) key exchange should be used instead.
.IP "\s-1SSL_OP_CIPHER_SERVER_PREFERENCE\s0" 4
.IX Item "SSL_OP_CIPHER_SERVER_PREFERENCE"
When choosing a cipher, use the server's preferences instead of the client
preferences. When not set, the \s-1SSL\s0 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.
.IP "\s-1SSL_OP_PKCS1_CHECK_1\s0" 4
.IX Item "SSL_OP_PKCS1_CHECK_1"
\&...
.IP "\s-1SSL_OP_PKCS1_CHECK_2\s0" 4
.IX Item "SSL_OP_PKCS1_CHECK_2"
\&...
.IP "\s-1SSL_OP_NETSCAPE_CA_DN_BUG\s0" 4
.IX Item "SSL_OP_NETSCAPE_CA_DN_BUG"
If we accept a netscape connection, demand a client cert, have a
non-self-signed \s-1CA\s0 which does not have its \s-1CA\s0 in netscape, and the
browser has a cert, it will crash/hang.  Works for 3.x and 4.xbeta 
.IP "\s-1SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG\s0" 4
.IX Item "SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG"
\&...
.IP "SSL_OP_NO_SSLv2" 4
.IX Item "SSL_OP_NO_SSLv2"
Do not use the SSLv2 protocol.
.IP "SSL_OP_NO_SSLv3" 4
.IX Item "SSL_OP_NO_SSLv3"
Do not use the SSLv3 protocol.
.IP "SSL_OP_NO_TLSv1" 4
.IX Item "SSL_OP_NO_TLSv1"
Do not use the TLSv1 protocol.
.IP "\s-1SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION\s0" 4
.IX 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.
.IP "\s-1SSL_OP_NO_TICKET\s0" 4
.IX 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.
.Sp
If this option is set this functionality is disabled and tickets will
not be used by clients or servers.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fISSL_CTX_set_options()\fR and \fISSL_set_options()\fR return the new options bitmask
after adding \fBoptions\fR.
.PP
\&\fISSL_CTX_get_options()\fR and \fISSL_get_options()\fR return the current bitmask.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fIssl\fR\|(3), \fISSL_new\fR\|(3), \fISSL_clear\fR\|(3),
\&\fISSL_CTX_set_tmp_dh_callback\fR\|(3),
\&\fISSL_CTX_set_tmp_rsa_callback\fR\|(3),
\&\fIdhparam\fR\|(1)
.SH "HISTORY"
.IX Header "HISTORY"
\&\fB\s-1SSL_OP_CIPHER_SERVER_PREFERENCE\s0\fR and
\&\fB\s-1SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION\s0\fR have been added in
OpenSSL 0.9.7.
.PP
\&\fB\s-1SSL_OP_TLS_ROLLBACK_BUG\s0\fR has been added in OpenSSL 0.9.6 and was automatically
enabled with \fB\s-1SSL_OP_ALL\s0\fR. As of 0.9.7, it is no longer included in \fB\s-1SSL_OP_ALL\s0\fR
and must be explicitly set.
.PP
\&\fB\s-1SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS\s0\fR 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).