SSL_CTX_set_cipher_list, SSL_set_cipher_list - choose list of available
int SSL_CTX_set_cipher_list(SSL_CTX *ctx, const char *str);
int 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
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 col-
lected 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 key.
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
DHE need a certificate and key and additional DH-parameters (see
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
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.
If the cipher list does not contain any SSLv2 cipher suites (this is
the default) then SSLv2 is effectively disabled and neither clients nor
servers will attempt to use SSLv2.
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),
1.0.2t 2019-09-10 SSL_CTX_set_cipher_list(3)
See also SSL_CTX_set_cipher_list(3)
Man(1) output converted with