Cryptography and SSL/TLS Toolkit



SSL_CTX_set1_groups, SSL_CTX_set1_groups_list, SSL_set1_groups, SSL_set1_groups_list, SSL_get1_groups, SSL_get_shared_group, SSL_CTX_set1_curves, SSL_CTX_set1_curves_list, SSL_set1_curves, SSL_set1_curves_list, SSL_get1_curves, SSL_get_shared_curve - EC supported curve functions


 #include <openssl/ssl.h>

 int SSL_CTX_set1_groups(SSL_CTX *ctx, int *glist, int glistlen);
 int SSL_CTX_set1_groups_list(SSL_CTX *ctx, char *list);

 int SSL_set1_groups(SSL *ssl, int *glist, int glistlen);
 int SSL_set1_groups_list(SSL *ssl, char *list);

 int SSL_get1_groups(SSL *ssl, int *groups);
 int SSL_get_shared_group(SSL *s, int n);

 int SSL_CTX_set1_curves(SSL_CTX *ctx, int *clist, int clistlen);
 int SSL_CTX_set1_curves_list(SSL_CTX *ctx, char *list);

 int SSL_set1_curves(SSL *ssl, int *clist, int clistlen);
 int SSL_set1_curves_list(SSL *ssl, char *list);

 int SSL_get1_curves(SSL *ssl, int *curves);
 int SSL_get_shared_curve(SSL *s, int n);


SSL_CTX_set1_groups() sets the supported groups for ctx to glistlen groups in the array glist. The array consist of all NIDs of groups in preference order. For a TLS client the groups are used directly in the supported groups extension. For a TLS server the groups are used to determine the set of shared groups.

SSL_CTX_set1_groups_list() sets the supported groups for ctx to string list. The string is a colon separated list of group NIDs or names, for example "P-521:P-384:P-256".

SSL_set1_groups() and SSL_set1_groups_list() are similar except they set supported groups for the SSL structure ssl.

SSL_get1_groups() returns the set of supported groups sent by a client in the supported groups extension. It returns the total number of supported groups. The groups parameter can be NULL to simply return the number of groups for memory allocation purposes. The groups array is in the form of a set of group NIDs in preference order. It can return zero if the client did not send a supported groups extension.

SSL_get_shared_group() returns shared group n for a server-side SSL ssl. If n is -1 then the total number of shared groups is returned, which may be zero. Other than for diagnostic purposes, most applications will only be interested in the first shared group so n is normally set to zero. If the value n is out of range, NID_undef is returned.

All these functions are implemented as macros.

The curve functions are synonyms for the equivalently named group functions and are identical in every respect. They exist because, prior to TLS1.3, there was only the concept of supported curves. In TLS1.3 this was renamed to supported groups, and extended to include Diffie Hellman groups. The group functions should be used in preference.


If an application wishes to make use of several of these functions for configuration purposes either on a command line or in a file it should consider using the SSL_CONF interface instead of manually parsing options.


SSL_CTX_set1_groups(), SSL_CTX_set1_groups_list(), SSL_set1_groups() and SSL_set1_groups_list(), return 1 for success and 0 for failure.

SSL_get1_groups() returns the number of groups, which may be zero.

SSL_get_shared_group() returns the NID of shared group n or NID_undef if there is no shared group n; or the total number of shared groups if n is -1.

When called on a client ssl, SSL_get_shared_group() has no meaning and returns -1.




The curve functions were first added to OpenSSL 1.0.2. The equivalent group functions were first added to OpenSSL 1.1.1.

Copyright 2013-2016 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (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