SSL_CTX_set_options, SSL_set_options, SSL_CTX_get_options,
SSL_get_options - manipulate SSL engine options
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);
SSL_CTX_set_options() adds the options set via bitmask in
options to ctx. Options already set before are not
SSL_set_options() adds the options set via bitmask in
options to ssl. Options already set before are not
SSL_CTX_get_options() returns the options set for ctx.
SSL_get_options() returns the options set for ssl.
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 settings.
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
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.
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
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
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.)
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
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:
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 openssl_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
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 DiffieHellman)
key exchange should be used instead.
If we accept a netscape connection, demand a client
cert, have a non-self-sighed CA which does not have
it's CA in netscape, and the browser has a cert, it
will crash/hang. Works for 3.x and 4.xbeta
Do not use the SSLv2 protocol.
Do not use the SSLv3 protocol.
Do not use the TLSv1 protocol.
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
ssl(3), SSL_new(3), SSL_clear(3), SSL_CTX_set_tmp_dh_callback(3), SSL_CTX_set_tmp_rsa_callback(3),
SSL_OP_TLS_ROLLBACK_BUG has been added in OpenSSL 0.9.6.
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).
2002-07-31 0.9.6g SSL_CTX_set_options(3)
[ Back ]