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 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() and SSL_set_cipher_list() 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 ciphers using DHE need a certificate and key and additional 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.

COPYRIGHT

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.

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