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======================================================================== Title "SSL_CTX_set_options 3" SSL_CTX_set_options 3 "2009-12-27" "1.1.0-dev" "OpenSSL"
For nroff, turn off justification. Always turn off hyphenation; it makes way too many mistakes in technical documents. "NAME"
SSL_CTX_set_options, SSL_set_options, SSL_CTX_clear_options, SSL_clear_options, SSL_CTX_get_options, SSL_get_options, SSL_get_secure_renegotiation_support - manipulate SSL options
"LIBRARY"
libcrypto, -lcrypto
"SYNOPSIS"
Header "SYNOPSIS" .Vb 1
#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_clear_options(SSL_CTX *ctx, long options);
long SSL_clear_options(SSL *ssl, long options);
\&
long SSL_CTX_get_options(SSL_CTX *ctx);
long SSL_get_options(SSL *ssl);
\&
long SSL_get_secure_renegotiation_support(SSL *ssl);
.Ve
"DESCRIPTION"
Header "DESCRIPTION" Note: all these functions are implemented using macros.
\fISSL_CTX_set_options() adds the options set via bitmask in options to ctx.
Options already set before are not cleared!
\fISSL_set_options() adds the options set via bitmask in options to ssl.
Options already set before are not cleared!
\fISSL_CTX_clear_options() clears the options set via bitmask in options
to ctx.
\fISSL_clear_options() clears the options set via bitmask in options to ssl.
\fISSL_CTX_get_options() returns the options set for ctx.
\fISSL_get_options() returns the options set for ssl.
\fISSL_get_secure_renegotiation_support() indicates whether the peer supports
secure renegotiation.
"NOTES"
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
or
operation (|).
\fISSL_CTX_set_options() and SSL_set_options() 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\|(3) and SSL_set_mode() functions.
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 SSL_new(), the current
option setting is copied. Changes to ctx do not affect already created
\s-1SSL\s0 objects. SSL_clear() does not affect the settings.
The following bug workaround options are available:
"\s-1SSL_OP_MICROSOFT_SESS_ID_BUG\s0" 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.
"\s-1SSL_OP_NETSCAPE_CHALLENGE_BUG\s0" 4
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.
"\s-1SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG\s0" 4
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 DES-CBC-SHA. So netscape, when
doing a re-connect, always takes the first cipher in the cipher list.
"\s-1SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG\s0" 4
Item "SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG" ...
"\s-1SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER\s0" 4
Item "SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER" ...
"\s-1SSL_OP_MSIE_SSLV2_RSA_PADDING\s0" 4
Item "SSL_OP_MSIE_SSLV2_RSA_PADDING" As of OpenSSL 0.9.7h and 0.9.8a, this option has no effect.
"\s-1SSL_OP_SSLEAY_080_CLIENT_DH_BUG\s0" 4
Item "SSL_OP_SSLEAY_080_CLIENT_DH_BUG" ...
"\s-1SSL_OP_TLS_D5_BUG\s0" 4
Item "SSL_OP_TLS_D5_BUG" ...
"\s-1SSL_OP_TLS_BLOCK_PADDING_BUG\s0" 4
Item "SSL_OP_TLS_BLOCK_PADDING_BUG" ...
"\s-1SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS\s0" 4
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.
"\s-1SSL_OP_ALL\s0" 4
Item "SSL_OP_ALL" All of the above bug workarounds.
It is usually safe to use \s-1SSL_OP_ALL\s0 to enable the bug workaround
options if compatibility with somewhat broken implementations is
desired.
The following modifying options are available:
"\s-1SSL_OP_TLS_ROLLBACK_BUG\s0" 4
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.)
"\s-1SSL_OP_SINGLE_DH_USE\s0" 4
Item "SSL_OP_SINGLE_DH_USE" Always create a new key when using
temporary/
ephemeral \s-1DH\s0 parameters
(see
SSL_CTX_set_tmp_dh_callback\|(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
openssl_dhparam\|(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 should therefore be enabled whenever
temporary/
ephemeral \s-1DH\s0 parameters are used.
"\s-1SSL_OP_EPHEMERAL_RSA\s0" 4
Item "SSL_OP_EPHEMERAL_RSA" Always use ephemeral (temporary) \s-1RSA\s0 key when doing \s-1RSA\s0 operations
(see
SSL_CTX_set_tmp_rsa_callback\|(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.
"\s-1SSL_OP_CIPHER_SERVER_PREFERENCE\s0" 4
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.
"\s-1SSL_OP_PKCS1_CHECK_1\s0" 4
Item "SSL_OP_PKCS1_CHECK_1" ...
"\s-1SSL_OP_PKCS1_CHECK_2\s0" 4
Item "SSL_OP_PKCS1_CHECK_2" ...
"\s-1SSL_OP_NETSCAPE_CA_DN_BUG\s0" 4
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
"\s-1SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG\s0" 4
Item "SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG" ...
"SSL_OP_NO_SSLv2" 4
Item "SSL_OP_NO_SSLv2" Do not use the SSLv2 protocol.
"SSL_OP_NO_SSLv3" 4
Item "SSL_OP_NO_SSLv3" Do not use the SSLv3 protocol.
"SSL_OP_NO_TLSv1" 4
Item "SSL_OP_NO_TLSv1" Do not use the TLSv1 protocol.
"\s-1SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION\s0" 4
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.
"\s-1SSL_OP_NO_TICKET\s0" 4
Item "SSL_OP_NO_TICKET" Normally clients and servers will, where possible, transparently make use
of RFC4507bis tickets for stateless session resumption.
.Sp
If this option is set this functionality is disabled and tickets will
not be used by clients or servers.
"\s-1SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION\s0" 4
Item "SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION" See the
\s-1SECURE\s0 \s-1RENEGOTIATION\s0 section for a discussion of the purpose of
this option
"SECURE RENEGOTIATION"
Header "SECURE RENEGOTIATION" OpenSSL 0.9.8m and later always attempts to use secure renegotiation as
described in draft-ietf-tls-renegotiation (\s-1FIXME:\s0 replace by \s-1RFC\s0). This
counters a prefix attack described in the draft and elsewhere (\s-1FIXME:\s0 need full
reference).
This attack has far reaching consequences which application writers should be
aware of. In the description below an implementation supporting secure
renegotiation is referred to as patched. A server not supporting secure
renegotiation is referred to as unpatched.
If an unpatched client attempts to connect to a patched OpenSSL server then
the attempt will succeed but renegotiation is not permitted. As required
by the standard a no_renegotiation alert is sent back to the client if
the \s-1TLS\s0 v1.0 protocol is used. If SSLv3.0 is used then renegotiation results
in a fatal handshake_failed alert.
If a patched OpenSSL client attempts to connect to an unpatched server
then the connection will fail because it is not possible to determine
whether an attack is taking place.
If the option \s-1SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION\s0 is set then the
above restrictions are relaxed. Renegotiation is permissible and initial
initial connections to unpatched servers will succeed.
This option should be used with caution because it leaves both clients and
servers vulnerable. However unpatched servers and clients are likely to be
around for some time and refusing to connect to unpatched servers or denying
renegotion altogether may be unacceptable. So applications may be forced to
tolerate unsafe renegotiation for the immediate future.
The function SSL_get_secure_renegotiation_support() indicates whether the peer
supports secure renegotiation.
The deprecated SSLv2 protocol does not support secure renegotiation at all.
"RETURN VALUES"
Header "RETURN VALUES" \fISSL_CTX_set_options() and
SSL_set_options() return the new options bitmask
after adding
options.
\fISSL_CTX_clear_options() and SSL_clear_options() return the new options bitmask
after clearing options.
\fISSL_CTX_get_options() and SSL_get_options() return the current bitmask.
\fISSL_get_secure_renegotiation_support() returns 1 is the peer supports
secure renegotiation and 0 if it does not.
"SEE ALSO"
Header "SEE ALSO" \fIssl\|(3),
SSL_new\|(3),
SSL_clear\|(3),
\fISSL_CTX_set_tmp_dh_callback\|(3),
\fISSL_CTX_set_tmp_rsa_callback\|(3),
\fIopenssl_dhparam\|(1)
"HISTORY"
Header "HISTORY" \fB\s-1SSL_OP_CIPHER_SERVER_PREFERENCE\s0 and
\fB\s-1SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION\s0 have been added in
OpenSSL 0.9.7.
\fB\s-1SSL_OP_TLS_ROLLBACK_BUG\s0 has been added in OpenSSL 0.9.6 and was automatically
enabled with \s-1SSL_OP_ALL\s0. As of 0.9.7, it is no longer included in \s-1SSL_OP_ALL\s0
and must be explicitly set.
\fB\s-1SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS\s0 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).
\fISSL_CTX_clear_options() and SSL_clear_options() were first added in OpenSSL
0.9.8m.
\fB\s-1SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION\s0 was first added in OpenSSL
0.9.8m.