=pod

=head1 NAME

SSL_CTX_set_cipher_list, SSL_set_cipher_list - choose list of available SSL_CIPHERs

=head1 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);

=head1 DESCRIPTION

SSL_CTX_set_cipher_list() sets the list of available ciphers for B<ctx>
using the control string B<str>. The format of the string is described
in L<ciphers(1)|ciphers(1)>. The list of ciphers is inherited by all
B<ssl> objects created from B<ctx>.

SSL_set_cipher_list() sets the list of ciphers only for B<ssl>.

=head1 NOTES

The control string B<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 unless the security level excludes it. 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
L<SSL_CTX_set_tmp_rsa_callback(3)|SSL_CTX_set_tmp_rsa_callback(3)>).
RSA ciphers using DHE need a certificate and key and additional DH-parameters
(see L<SSL_CTX_set_tmp_dh_callback(3)|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 L<SSL_CTX_set_tmp_dh_callback(3)|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.

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.

=head1 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.

=head1 SEE ALSO

L<ssl(3)|ssl(3)>, L<SSL_get_ciphers(3)|SSL_get_ciphers(3)>,
L<SSL_CTX_use_certificate(3)|SSL_CTX_use_certificate(3)>,
L<SSL_CTX_set_tmp_rsa_callback(3)|SSL_CTX_set_tmp_rsa_callback(3)>,
L<SSL_CTX_set_tmp_dh_callback(3)|SSL_CTX_set_tmp_dh_callback(3)>,
L<ciphers(1)|ciphers(1)>

=cut
