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
LIBRARY
libcrypto, -lcrypto
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() func- tions. 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 2002-07-31 0.9.6g 1 SSL_CTX_set_options(3) OpenSSL SSL_CTX_set_options(3) 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 estab- lished 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://mer- chant.netscape.com) has this bug. It only really shows up when connecting via SSLv2/v3 then reconnect- ing 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-con- nect, 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 2002-07-31 0.9.6g 2 SSL_CTX_set_options(3) OpenSSL SSL_CTX_set_options(3) this rule by adapting to the server's answer. (Exam- ple: 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 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 recom- mended. 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 opera- tions (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 interoper- ability 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 ... 2002-07-31 0.9.6g 3 SSL_CTX_set_options(3) OpenSSL SSL_CTX_set_options(3) 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-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 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
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), openssl_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). 2002-07-31 0.9.6g 4
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