SSL_CTX_set_cipher_list, SSL_set_cipher_list — choose list of available SSL_CIPHERs
SSL_CTX_set_cipher_list(SSL_CTX *ctx, const char *str);
SSL_set_cipher_list(SSL *ssl, const char *str);
SSL_CTX_set_cipher_list() sets the list of available ciphers
for ctx using the control string str. The format of the string is
described in ciphers(1). The list of ciphers is
inherited by all ssl objects created from ctx.
SSL_set_cipher_list() sets the list of ciphers only for ssl.
The control string str should be universally usable and not
depend on details of the library configuration (ciphers compiled
in). Thus no syntax checking takes place. Items that are not recognized,
because the corresponding ciphers are not compiled in or because
they are mistyped, are simply ignored. Failure is only flagged if
no ciphers could be collected at all.
It should be noted, that inclusion of a cipher to be used
into the list is a necessary condition. On the client side, the
inclusion into the list is also sufficient. On the server side,
additional restrictions apply. All ciphers have additional requirements.
ADH ciphers don't need a certificate, but DH-parameters must have
been set. All other ciphers need a corresponding certificate and
A RSA cipher can only be chosen, when a RSA certificate is
available. RSA export ciphers with a keylength of 512 bits for the
RSA key require a temporary 512 bit RSA key, as typically the supplied
key has a length of 1024 bit (see SSL_CTX_set_tmp_rsa_callback(3)). RSA ciphers using EDH
need a certificate and key and additional DH-parameters (see SSL_CTX_set_tmp_dh_callback(3)).
A DSA cipher can only be chosen, when a DSA certificate is
available. DSA ciphers always use DH key exchange and therefore
need DH-parameters (see SSL_CTX_set_tmp_dh_callback(3)).
When these conditions are not met for any cipher in the list
(e.g. a client only supports export RSA ciphers with a asymmetric
key length of 512 bits and the server is not configured to use temporary
RSA keys), the "no shared cipher" (SSL_R_NO_SHARED_CIPHER) error
is generated and the handshake will fail.
SSL_CTX_set_cipher_list() and SSL_set_cipher_list() return
1 if any cipher could be selected and 0 on complete failure.
ssl(3), SSL_get_ciphers(3), SSL_CTX_use_certificate(3), SSL_CTX_set_tmp_rsa_callback(3), SSL_CTX_set_tmp_dh_callback(3), ciphers(1)