SSL_CTX_set_options(3) OpenSSL 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);
DESCRIPTIONSSL_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 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_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_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.
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(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_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 it's 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 VALUESSSL_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 ALSOssl(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_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).
3rd Berkeley Distribution 0.9.6m SSL_CTX_set_options(3)