/xlv3/openssl/0.9.7e-sgipl1/work/0.9.7e-sgipl1/openssl-
0.9.7e/doc/ssl
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NAME
SSL_CTX_set_options, SSL_set_options, SSL_CTX_get_options,
SSL_get_options - manipulate SSL engine options
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) 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:
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.
SSL_OP_NETSCAPE_CHALLENGE_BUG
Netscape-Commerce/1.12, when talking SSLv2, accepts a 32
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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.
SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG
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
7.6.1.3, 'cipher_suite'.
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....
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 list.
SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG
...
SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER
...
SSL_OP_MSIE_SSLV2_RSA_PADDING
...
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 vulnerability affecting CBC ciphers, which
cannot be handled by some broken SSL implementations.
This option has no effect for connections using other
ciphers.
SSL_OP_ALL
All of the above bug workarounds.
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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 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
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 used.
SSL_OP_EPHEMERAL_RSA
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
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 protocol, for
SSLv2 the server will send his list of preferences to
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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 session (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 bitmask 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_RESUMPTION_ON_RENEGOTIATION have been
added in OpenSSL 0.9.7.
SSL_OP_TLS_ROLLBACK_BUG has been added in OpenSSL 0.9.6 and
was automatically enabled with SSL_OP_ALL. As of 0.9.7, it
is no longer included in SSL_OP_ALL and must be explicitly
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set.
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).
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