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SSL_CTX_set_options(3)
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
The SSL_CTX_set_options() function adds the options set via bitmask in
options to ctx. Options already set before are not cleared.
The SSL_set_options() function adds the options set via bitmask in options
to ssl. Options already set before are not cleared.
The SSL_CTX_get_options() function returns the options set for ctx.
The SSL_get_options() function returns the options set for ssl.
NOTES
The behavior 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; they can never be reset.
The SSL_CTX_set_options() and SSL_set_options() functions affect the
(external) protocol behavior of the SSL library. The (internal) behavior
of the API can be changed by using the similar SSL_CTX_set_mode() 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. The SSL_clear() function 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-byte
challenge but then appears to only use 16 bytes when generating the
encryption keys. Using 16 bytes is acceptable, but it should be
acceptable also to use 32. According to SSLv3 specifications, you
should use 32 bytes for the challenge when operating in SSLv2/v3
compatibility mode, but this breaks the server. So, 16 bytes is
preferable.
SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG
ssl3.netscape.com:443, first a connection is established with RC4-
MD5. If it resumes, you use 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 shows up when connecting via SSLv2/v3 then
reconnecting via SSLv3. The cipher list changes.
Try connecting with a cipher list of DES-CBC-SHA:RC4-MD5. Each new
connection uses RC4-MD5, but a reconnect tries to use DES-CBC-SHA.
So, Netscape always takes the first cipher in the cipher list when
doing a reconnect.
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_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 an 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_DONT_INSERT_EMPTY_FRAGMENTS
Disables a countermeasure against an 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.
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_SINGLE_DH_USE
Always create a new key when using temporary/ephemeral DH
parameters (see SSL_CTX_set_tmp_dh_callback()). 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()). If "strong" primes were
used, it is not necessary to generate a new DH key during each
handshake, but it is 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()). According to the
specifications, this is only done when an 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. Therefore, it should never be used. Ciphers
with EDH (ephemeral Diffie-Hellman) key exchange should be used
instead.
SSL_OP_PKCS1_CHECK_1
...
SSL_OP_PKCS1_CHECK_2
...
SSL_OP_NETSCAPE_CA_DN_BUG
If you 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.
RETURN VALUES
The SSL_CTX_set_options() and SSL_set_options() functions return the new
options bitmask after adding options.
The SSL_CTX_get_options() and SSL_get_options() functions return the
current bitmask.
HISTORY
SSL_OP_TLS_ROLLBACK_BUG was 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.
SEE ALSO
Commands: dhparam(1)
Functions: ssl(3), SSL_CTX_set_tmp_dh_callback(3),
SSL_CTX_set_tmp_rsa_callback(3), SSL_new(3), SSL_clear(3)
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