1.\" 2.\" $OpenBSD: SSL_CTX_set_cipher_list.3,v 1.1 2016/11/05 15:32:19 schwarze Exp $ 3.\" 4.Dd $Mdocdate: November 5 2016 $ 5.Dt SSL_CTX_SET_CIPHER_LIST 3 6.Os 7.Sh NAME 8.Nm SSL_CTX_set_cipher_list , 9.Nm SSL_set_cipher_list 10.Nd choose list of available SSL_CIPHERs 11.Sh SYNOPSIS 12.In openssl/ssl.h 13.Ft int 14.Fn SSL_CTX_set_cipher_list "SSL_CTX *ctx" "const char *str" 15.Ft int 16.Fn SSL_set_cipher_list "SSL *ssl" "const char *str" 17.Sh DESCRIPTION 18.Fn SSL_CTX_set_cipher_list 19sets the list of available ciphers for 20.Fa ctx 21using the control string 22.Fa str . 23The format of the string is described 24in 25.Xr openssl 1 . 26The list of ciphers is inherited by all 27.Fa ssl 28objects created from 29.Fa ctx . 30.Pp 31.Fn SSL_set_cipher_list 32sets the list of ciphers only for 33.Fa ssl . 34.Sh NOTES 35The control string 36.Fa str 37should be universally usable and not depend on details of the library 38configuration (ciphers compiled in). 39Thus no syntax checking takes place. 40Items that are not recognized, because the corresponding ciphers are not 41compiled in or because they are mistyped, are simply ignored. 42Failure is only flagged if no ciphers could be collected at all. 43.Pp 44It should be noted that inclusion of a cipher to be used into the list is a 45necessary condition. 46On the client side, the inclusion into the list is also sufficient. 47On the server side, additional restrictions apply. 48All ciphers have additional requirements. 49ADH ciphers don't need a certificate, but DH-parameters must have been set. 50All other ciphers need a corresponding certificate and key. 51.Pp 52A RSA cipher can only be chosen when a RSA certificate is available. 53RSA export ciphers with a keylength of 512 bits for the RSA key require a 54temporary 512 bit RSA key, as typically the supplied key has a length of 1024 55bits (see 56.Xr SSL_CTX_set_tmp_rsa_callback 3 ) . 57RSA ciphers using EDH need a certificate and key and additional DH-parameters 58(see 59.Xr SSL_CTX_set_tmp_dh_callback 3 ) . 60.Pp 61A DSA cipher can only be chosen when a DSA certificate is available. 62DSA ciphers always use DH key exchange and therefore need DH-parameters (see 63.Xr SSL_CTX_set_tmp_dh_callback 3 ) . 64.Pp 65When these conditions are not met for any cipher in the list (for example, a 66client only supports export RSA ciphers with an asymmetric key length of 512 67bits and the server is not configured to use temporary RSA keys), the 68.Dq no shared cipher 69.Pq Dv SSL_R_NO_SHARED_CIPHER 70error is generated and the handshake will fail. 71.Sh RETURN VALUES 72.Fn SSL_CTX_set_cipher_list 73and 74.Fn SSL_set_cipher_list 75return 1 if any cipher could be selected and 0 on complete failure. 76.Sh SEE ALSO 77.Xr ciphers 1 , 78.Xr ssl 3 , 79.Xr SSL_CTX_set_tmp_dh_callback 3 , 80.Xr SSL_CTX_set_tmp_rsa_callback 3 , 81.Xr SSL_CTX_use_certificate 3 , 82.Xr SSL_get_ciphers 3 83