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.
the cipher list.
SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG
...
SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER
...
SSL_OP_MSIE_SSLV2_RSA_PADDING
As of OpenSSL 0.9.7h and 0.9.8a, this option has no effect.
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
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 its 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.
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