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SSL_CTX_set_cipher_list, SSL_set_cipher_listchoose list of available SSL_CIPHERs

#include <openssl/ssl.h>

SSL_CTX_set_cipher_list(SSL_CTX *ctx, const char *str);

SSL_set_cipher_list(SSL *ssl, const char *str);

() 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.

() sets the list of ciphers only for ssl.

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 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 (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.

SSL_CTX_set_cipher_list() and SSL_set_cipher_list() return 1 if any cipher could be selected and 0 on complete failure.

ssl(3), SSL_CTX_set1_groups(3), SSL_CTX_set_tmp_dh_callback(3), SSL_CTX_use_certificate(3), SSL_get_ciphers(3)

SSL_CTX_set_cipher_list() and SSL_set_cipher_list() appeared before SSLeay 0.8 and have been available since OpenBSD 2.4.

March 21, 2018 OpenBSD-6.3