#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_clear_options(SSL_CTX *ctx, long options); long SSL_clear_options(SSL *ssl, long options); long SSL_CTX_get_options(SSL_CTX *ctx); long SSL_get_options(SSL *ssl); long SSL_get_secure_renegotiation_support(SSL *ssl);
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_clear_options() clears the options set via bitmask in options to ctx.
SSL_clear_options() clears the options set via bitmask in options to ssl.
SSL_CTX_get_options() returns the options set for ctx.
SSL_get_options() returns the options set for ssl.
SSL_get_secure_renegotiation_support() indicates whether the peer supports secure renegotiation.
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:
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.
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:
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.)
If this option is set this functionality is disabled and tickets will not be used by clients or servers.
The deprecated and highly broken SSLv2 protocol does not support renegotiation at all: its use is strongly discouraged.
This attack has far reaching consequences which application writers should be aware of. In the description below an implementation supporting secure renegotiation is referred to as patched. A server not supporting secure renegotiation is referred to as unpatched.
The following sections describe the operations permitted by OpenSSL's secure renegotiation implementation.
If the patched OpenSSL server attempts to renegotiate a fatal handshake_failure alert is sent. This is because the server code may be unaware of the unpatched nature of the client.
If the option SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION is set then renegotiation always succeeds.
NB: a bug in OpenSSL clients earlier than 0.9.8m (all of which are unpatched) will result in the connection hanging if it receives a no_renegotiation alert. OpenSSL versions 0.9.8m and later will regard a no_renegotiation alert as fatal and respond with a fatal handshake_failure alert. This is because the OpenSSL API currently has no provision to indicate to an application that a renegotiation attempt was refused.
The option SSL_OP_LEGACY_SERVER_CONNECT is currently set by default even though it has security implications: otherwise it would be impossible to connect to unpatched servers (i.e. all of them initially) and this is clearly not acceptable. Renegotiation is permitted because this does not add any additional security issues: during an attack clients do not see any renegotiations anyway.
As more servers become patched the option SSL_OP_LEGACY_SERVER_CONNECT will not be set by default in a future version of OpenSSL.
OpenSSL client applications wishing to ensure they can connect to unpatched servers should always set SSL_OP_LEGACY_SERVER_CONNECT
OpenSSL client applications that want to ensure they can not connect to unpatched servers (and thus avoid any security issues) should always clear SSL_OP_LEGACY_SERVER_CONNECT using SSL_CTX_clear_options() or SSL_clear_options().
The difference between the SSL_OP_LEGACY_SERVER_CONNECT and SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION options is that SSL_OP_LEGACY_SERVER_CONNECT enables initial connections and secure renegotiation between OpenSSL clients and unpatched servers only, while SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION allows initial connections and renegotiation between OpenSSL and unpatched clients or servers.
SSL_CTX_clear_options() and SSL_clear_options() return the new options bitmask after clearing options.
SSL_CTX_get_options() and SSL_get_options() return the current bitmask.
SSL_get_secure_renegotiation_support() returns 1 is the peer supports secure renegotiation and 0 if it does not.
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 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).
SSL_CTX_clear_options() and SSL_clear_options() were first added in OpenSSL 0.9.8m.
SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION, SSL_OP_LEGACY_SERVER_CONNECT and the function SSL_get_secure_renegotiation_support() were first added in OpenSSL 0.9.8m.