SSL_CTX_SET1_CURVES(3ossl) OpenSSL SSL_CTX_SET1_CURVES(3ossl)
NAME
SSL_CTX_set1_groups, SSL_CTX_set1_groups_list, SSL_set1_groups,
SSL_set1_groups_list, SSL_get1_groups, SSL_get0_iana_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_get0_iana_groups(SSL *ssl, uint16_t **out);
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 supported
groups. Currently supported groups for TLSv1.3 are
NID_X9_62_prime256v1, NID_secp384r1, NID_secp521r1, NID_X25519,
NID_X448, NID_brainpoolP256r1tls13, NID_brainpoolP384r1tls13,
NID_brainpoolP512r1tls13, NID_ffdhe2048, NID_ffdhe3072, NID_ffdhe4096,
NID_ffdhe6144 and NID_ffdhe8192. OpenSSL will use this array in
different ways depending on TLS role and version:
For a TLS client, the groups are used directly in the supported groups
extension. The extension's preference order, to be evaluated by the
server, is determined by the order of the elements in the array.
For a TLS 1.2 server, the groups determine the selected group. If
SSL_OP_CIPHER_SERVER_PREFERENCE is set, the order of the elements in
the array determines the selected group. Otherwise, the order is
ignored and the client's order determines the selection.
For a TLS 1.3 server, the groups determine the selected group, but
selection is more complex. A TLS 1.3 client sends both a group list as
well as a predicted subset of groups. Choosing a group outside the
predicted subset incurs an extra roundtrip. However, in some
situations, the most preferred group may not be predicted. OpenSSL
considers all supported groups to be comparable in security and
prioritizes avoiding roundtrips above either client or server
preference order. If an application uses an external provider to extend
OpenSSL with, e.g., a post-quantum algorithm, this behavior may allow a
network attacker to downgrade connections to a weaker algorithm.
SSL_CTX_set1_groups_list() sets the supported groups for ctx to string
list. The string is a colon separated list of group names, for example
"P-521:P-384:P-256:X25519:ffdhe2048". The groups are used as in
SSL_CTX_set1_groups(), described above. Currently supported groups for
TLSv1.3 are P-256, P-384, P-521, X25519, X448, brainpoolP256r1tls13,
brainpoolP384r1tls13, brainpoolP512r1tls13, ffdhe2048, ffdhe3072,
ffdhe4096, ffdhe6144 and ffdhe8192. Support for other groups may be
added by external providers, however note the discussion on TLS 1.3
selection criteria above. If a group name is preceded with the "?"
character, it will be ignored if an implementation is missing.
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_get0_iana_groups() retrieves the list of groups sent by the client
in the supported_groups extension. The *out array of bytes is
populated with the host-byte-order representation of the uint16_t group
identifiers, as assigned by IANA. The group list is returned in the
same order that was received in the ClientHello. The return value is
the number of groups, not the number of bytes written.
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_get0_iana_groups() returns the number of (uint16_t) 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.
Support for ignoring unknown groups in SSL_CTX_set1_groups_list() and
SSL_set1_groups_list() was added in OpenSSL 3.3.
Earlier versions of this document described the list as a preference
order. However, OpenSSL's behavior as a TLS 1.3 server is to consider
all supported groups as comparable in security.
COPYRIGHT
Copyright 2013-2024 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>.
3.3.2 2024-09-04 SSL_CTX_SET1_CURVES(3ossl)
openssl 3.3.2 - Generated Tue Sep 24 13:56:03 CDT 2024