NAME
SSL_CTX_set_cipher_list,
SSL_set_cipher_list —
choose list of available
SSL_CIPHERs
SYNOPSIS
#include
<openssl/ssl.h>
int
SSL_CTX_set_cipher_list(SSL_CTX
*ctx, const char
*str);
int
SSL_set_cipher_list(SSL
*ssl, const char
*str);
DESCRIPTION
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
openssl(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.
NOTES
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 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 bits (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 (for
example, a client only supports export RSA ciphers with an 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.
RETURN VALUES
SSL_CTX_set_cipher_list() and
SSL_set_cipher_list() return 1 if any cipher could
be selected and 0 on complete failure.
SEE ALSO
ciphers(1), ssl(3), SSL_CTX_set_tmp_dh_callback(3), SSL_CTX_set_tmp_rsa_callback(3), SSL_CTX_use_certificate(3), SSL_get_ciphers(3)