NAME

       SSL_CTX_set1_groups, SSL_CTX_set1_groups_list, SSL_set1_groups, SSL_set1_groups_list,
       SSL_get1_groups, SSL_get_shared_group, SSL_get_negotiated_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

SYNOPSIS

        #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_get_negotiated_group(SSL *s);

        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);

DESCRIPTION

       For all of the functions below that set the supported groups there must be at least one
       group in the list. A number of these functions identify groups via a unique integer NID
       value. However, support for some groups may be added by external providers. In this case
       there will be no NID assigned for the group.  When setting such groups applications should
       use the "list" form of these functions (i.e. SSL_CTX_set1_groups_list() and
       SSL_set1_groups_list).

       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. Currently supported groups for TLSv1.3 are
       NID_X9_62_prime256v1, NID_secp384r1, NID_secp521r1, NID_X25519, NID_X448, NID_ffdhe2048,
       NID_ffdhe3072, NID_ffdhe4096, NID_ffdhe6144 and NID_ffdhe8192.

       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:X25519:ffdhe2048". Currently supported groups for TLSv1.3 are P-256,
       P-384, P-521, X25519, X448, ffdhe2048, ffdhe3072, ffdhe4096, ffdhe6144, ffdhe8192. Support
       for other groups may be added by external providers.

       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. If a supported group NID is
       unknown then the value is set to the bitwise OR of TLSEXT_nid_unknown (0x1000000) and the
       id of the group.

       SSL_get_shared_group() returns the NID of the 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.
       If the NID for the shared group is unknown then the value is set to the bitwise OR of
       TLSEXT_nid_unknown (0x1000000) and the id of the group.

       SSL_get_negotiated_group() returns the NID of the negotiated group used for the handshake
       key exchange process.  For TLSv1.3 connections this typically reflects the state of the
       current connection, though in the case of PSK-only resumption, the returned value will be
       from a previous connection.  For earlier TLS versions, when a session has been resumed, it
       always reflects the group used for key exchange during the initial handshake (otherwise it
       is from the current, non-resumption, connection).  This can be called by either client or
       server. If the NID for the shared group is unknown then the value is set to the bitwise OR
       of TLSEXT_nid_unknown (0x1000000) and the id of the group.

       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.

NOTES

       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.

RETURN VALUES

       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.

       SSL_get_negotiated_group() returns the NID of the negotiated group used for key exchange,
       or NID_undef if there was no negotiated group.

SEE ALSO

       ssl(7), SSL_CTX_add_extra_chain_cert(3)

HISTORY

       The curve functions were added in OpenSSL 1.0.2. The equivalent group functions were added
       in OpenSSL 1.1.1. The SSL_get_negotiated_group() function was added in OpenSSL 3.0.0.

COPYRIGHT

       Copyright 2013-2021 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>.