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.\" ========================================================================
.\"
.IX Title "SSL_CTX_set_cipher_list 3"
.TH SSL_CTX_set_cipher_list 3 "2019-12-20" "1.0.2u" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.nh
.SH "NAME"
SSL_CTX_set_cipher_list, SSL_set_cipher_list \- choose list of available SSL_CIPHERs
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #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);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fBSSL_CTX_set_cipher_list()\fR sets the list of available ciphers for \fBctx\fR
using the control string \fBstr\fR. The format of the string is described
in \fBciphers\fR\|(1). The list of ciphers is inherited by all
\&\fBssl\fR objects created from \fBctx\fR.
.PP
\&\fBSSL_set_cipher_list()\fR sets the list of ciphers only for \fBssl\fR.
.SH "NOTES"
.IX Header "NOTES"
The control string \fBstr\fR 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.
.PP
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. \s-1ADH\s0 ciphers don't need a certificate, but
DH-parameters must have been set. All other ciphers need a corresponding
certificate and key.
.PP
A \s-1RSA\s0 cipher can only be chosen, when a \s-1RSA\s0 certificate is available.
\&\s-1RSA\s0 export ciphers with a keylength of 512 bits for the \s-1RSA\s0 key require
a temporary 512 bit \s-1RSA\s0 key, as typically the supplied key has a length
of 1024 bit (see
\&\fBSSL_CTX_set_tmp_rsa_callback\fR\|(3)).
\&\s-1RSA\s0 ciphers using \s-1DHE\s0 need a certificate and key and additional DH-parameters
(see \fBSSL_CTX_set_tmp_dh_callback\fR\|(3)).
.PP
A \s-1DSA\s0 cipher can only be chosen, when a \s-1DSA\s0 certificate is available.
\&\s-1DSA\s0 ciphers always use \s-1DH\s0 key exchange and therefore need DH-parameters
(see \fBSSL_CTX_set_tmp_dh_callback\fR\|(3)).
.PP
When these conditions are not met for any cipher in the list (e.g. a
client only supports export \s-1RSA\s0 ciphers with a asymmetric key length
of 512 bits and the server is not configured to use temporary \s-1RSA\s0
keys), the \*(L"no shared cipher\*(R" (\s-1SSL_R_NO_SHARED_CIPHER\s0) error is generated
and the handshake will fail.
.PP
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.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fBSSL_CTX_set_cipher_list()\fR and \fBSSL_set_cipher_list()\fR return 1 if any cipher
could be selected and 0 on complete failure.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBssl\fR\|(3), \fBSSL_get_ciphers\fR\|(3),
\&\fBSSL_CTX_use_certificate\fR\|(3),
\&\fBSSL_CTX_set_tmp_rsa_callback\fR\|(3),
\&\fBSSL_CTX_set_tmp_dh_callback\fR\|(3),
\&\fBciphers\fR\|(1)