NAME

       SSL_CTX_set_cipher_list, SSL_set_cipher_list, SSL_CTX_set_ciphersuites,
       SSL_set_ciphersuites, OSSL_default_cipher_list, OSSL_default_ciphersuites - 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);

        int SSL_CTX_set_ciphersuites(SSL_CTX *ctx, const char *str);
        int SSL_set_ciphersuites(SSL *s, const char *str);

        const char *OSSL_default_cipher_list(void);
        const char *OSSL_default_ciphersuites(void);

DESCRIPTION

       SSL_CTX_set_cipher_list() sets the list of available ciphers (TLSv1.2 and below) for ctx
       using the control string str. The format of the string is described in openssl-ciphers(1).
       The list of ciphers is inherited by all ssl objects created from ctx. This function does
       not impact TLSv1.3 ciphersuites. Use SSL_CTX_set_ciphersuites() to configure those.

       SSL_set_cipher_list() sets the list of ciphers (TLSv1.2 and below) only for ssl.

       SSL_CTX_set_ciphersuites() is used to configure the available TLSv1.3 ciphersuites for
       ctx. This is a simple colon (":") separated list of TLSv1.3 ciphersuite names in order of
       preference. Valid TLSv1.3 ciphersuite names are:

       TLS_AES_128_GCM_SHA256
       TLS_AES_256_GCM_SHA384
       TLS_CHACHA20_POLY1305_SHA256
       TLS_AES_128_CCM_SHA256
       TLS_AES_128_CCM_8_SHA256

       An empty list is permissible. The default value for the this setting is:

       "TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256:TLS_AES_128_GCM_SHA256"

       SSL_set_ciphersuites() is the same as SSL_CTX_set_ciphersuites() except it configures the
       ciphersuites for ssl.

       OSSL_default_cipher_list() returns the default cipher string for TLSv1.2 (and earlier)
       ciphers. OSSL_default_ciphersuites() returns the default cipher string for TLSv1.3
       ciphersuites.

NOTES

       The control string str for SSL_CTX_set_cipher_list(), SSL_set_cipher_list(),
       SSL_CTX_set_ciphersuites() and SSL_set_ciphersuites() 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.

       An RSA cipher can only be chosen, when an RSA certificate is available.  RSA ciphers using
       DHE 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 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.

       OSSL_default_cipher_list() and OSSL_default_ciphersuites() replace SSL_DEFAULT_CIPHER_LIST
       and TLS_DEFAULT_CIPHERSUITES, respectively. The cipher list defines are deprecated as of
       3.0.

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.

       SSL_CTX_set_ciphersuites() and SSL_set_ciphersuites() return 1 if the requested
       ciphersuite list was configured, and 0 otherwise.

SEE ALSO

       ssl(7), SSL_get_ciphers(3), SSL_CTX_use_certificate(3), SSL_CTX_set_tmp_dh_callback(3),
       openssl-ciphers(1)

HISTORY

       OSSL_default_cipher_list() and OSSL_default_ciphersites() are new in 3.0.

COPYRIGHT

       Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the Apache License 2.0 (the "License").  You may not use this file except
       in compliance with the License.  You can obtain a copy in the file LICENSE in the source
       distribution or at <https://www.openssl.org/source/license.html>.