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NAMESSL_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
#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);
DESCRIPTIONNote: all these functions are implemented using macros.
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_clear_options() clears the options set via bitmask in options to ctx.
SSL_clear_options() clears the options set via bitmask in options to ssl.
SSL_CTX_get_options() returns the options set for ctx.
SSL_get_options() returns the options set for ssl.
SSL_get_secure_renegotiation_support() indicates whether the peer supports secure renegotiation.
NOTESThe behaviour of the
SSL_CTX_set_options() and SSL_set_options() affect the (external) protocol behaviour of the
During a handshake, the option settings of the
The following bug workaround options are available:
- 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.
- 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.
- As of OpenSSL 0.9.8q and 1.0.0c, this option has no effect.
Don't prefer ECDHE-ECDSA ciphers when the client appears to be Safari on OS X. OS X 10.8..10.8.3has broken support for ECDHE-ECDSA ciphers.
Disables a countermeasure against a SSL 3.0/TLS 1.0protocol vulnerability affectingCBCciphers, which cannot be handled by some brokenSSLimplementations. This option has no effect for connections using other ciphers.
- Adds a padding extension to ensure the ClientHello size is never between 256 and 511 bytes in length. This is needed as a workaround for some implementations.
- All of the above bug workarounds.
It is usually safe to use
The following modifying options are available:
Disable version rollback attack detection.
During the client key exchange, the client must send the same information about acceptableSSL/TLSprotocol 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.)
Always create a new key when using temporary/ephemeral DHparameters (see SSL_CTX_set_tmp_dh_callback(3)). This option must be used to prevent small subgroup attacks, when theDHparameters 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 newDHkey during each handshake but it is also recommended.SSL_OP_SINGLE_DH_USEshould therefore be enabled whenever temporary/ephemeralDHparameters are used.
- This option is no longer implemented and is treated as no op.
When choosing a cipher, use the server's preferences instead of the client
preferences. When not set, the SSLserver 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.
If we accept a netscape connection, demand a client cert, have a
non-self-signed CAwhich does not have itsCAin netscape, and the browser has a cert, it will crash/hang. Works for 3.x and 4.xbeta
- Do not use the SSLv2 protocol. As of OpenSSL 1.0.2g the SSL_OP_NO_SSLv2 option is set by default.
- Do not use the SSLv3 protocol. It is recommended that applications should set this option.
- Do not use the TLSv1 protocol.
- Do not use the TLSv1.1 protocol.
- Do not use the TLSv1.2 protocol.
- 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.
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.
Allow legacy insecure renegotiation between OpenSSL and unpatched clients or
servers. See the SECURE RENEGOTIATIONsection for more details.
Allow legacy insecure renegotiation between OpenSSL and unpatched servers
only: this option is currently set by default. See the
SECURE RENEGOTIATIONsection for more details.
SECURE RENEGOTIATIONOpenSSL 0.9.8m and later always attempts to use secure renegotiation as described in
The deprecated and highly broken SSLv2 protocol does not support renegotiation at all: its use is strongly discouraged.
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.
The following sections describe the operations permitted by OpenSSL's secure renegotiation implementation.
Patched client and serverConnections and renegotiation are always permitted by OpenSSL implementations.
Unpatched client and patched OpenSSL serverThe initial connection succeeds but client renegotiation is denied by the server with a no_renegotiation warning alert if
If the patched OpenSSL server attempts to renegotiate a fatal handshake_failure alert is sent. This is because the server code may be unaware of the unpatched nature of the client.
If the option
Patched OpenSSL client and unpatched server.If the option
As more servers become patched the option
OpenSSL client applications wishing to ensure they can connect to unpatched servers should always set
OpenSSL client applications that want to ensure they can not connect to unpatched servers (and thus avoid any security issues) should always clear
The difference between the
RETURN VALUESSSL_CTX_set_options() and SSL_set_options() return the new options bitmask after adding options.
SSL_CTX_clear_options() and SSL_clear_options() return the new options bitmask after clearing options.
SSL_CTX_get_options() and SSL_get_options() return the current bitmask.
SSL_get_secure_renegotiation_support() returns 1 is the peer supports secure renegotiation and 0 if it does not.
SEE ALSOssl(3), SSL_new(3), SSL_clear(3), SSL_CTX_set_tmp_dh_callback(3), SSL_CTX_set_tmp_rsa_callback(3), dhparam(1)
SSL_CTX_clear_options() and SSL_clear_options() were first added in OpenSSL 0.9.8m.