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It can be useful to know what group was used for the handshake's key exchange process even on non-TLS 1.3 connections. Allow this API, new in OpenSSL 3.0.0, to be used on other TLS versions as well. Since pre-TLS-1.3 key exchange occurs only on full handshakes, this necessitates adding a field to the SSL_SESSION object to carry the group information across resumptions. The key exchange group in the SSL_SESSION can also be relevant in TLS 1.3 when the resumption handshake uses the "psk_ke" key-exchange mode, so also track whether a fresh key exchange was done for TLS 1.3. Since the new field is optional in the ASN.1 sense, there is no need to increment SSL_SESSION_ASN1_VERSION (which incurs strong incompatibility churn). Reviewed-by: Matt Caswell <matt@openssl.org> (Merged from https://github.com/openssl/openssl/pull/14750)
142 lines
6.1 KiB
Plaintext
142 lines
6.1 KiB
Plaintext
=pod
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=head1 NAME
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SSL_CTX_set1_groups, SSL_CTX_set1_groups_list, SSL_set1_groups,
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SSL_set1_groups_list, SSL_get1_groups, SSL_get_shared_group,
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SSL_get_negotiated_group, SSL_CTX_set1_curves, SSL_CTX_set1_curves_list,
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SSL_set1_curves, SSL_set1_curves_list, SSL_get1_curves, SSL_get_shared_curve
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- EC supported curve functions
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=head1 SYNOPSIS
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#include <openssl/ssl.h>
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int SSL_CTX_set1_groups(SSL_CTX *ctx, int *glist, int glistlen);
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int SSL_CTX_set1_groups_list(SSL_CTX *ctx, char *list);
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int SSL_set1_groups(SSL *ssl, int *glist, int glistlen);
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int SSL_set1_groups_list(SSL *ssl, char *list);
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int SSL_get1_groups(SSL *ssl, int *groups);
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int SSL_get_shared_group(SSL *s, int n);
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int SSL_get_negotiated_group(SSL *s);
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int SSL_CTX_set1_curves(SSL_CTX *ctx, int *clist, int clistlen);
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int SSL_CTX_set1_curves_list(SSL_CTX *ctx, char *list);
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int SSL_set1_curves(SSL *ssl, int *clist, int clistlen);
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int SSL_set1_curves_list(SSL *ssl, char *list);
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int SSL_get1_curves(SSL *ssl, int *curves);
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int SSL_get_shared_curve(SSL *s, int n);
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=head1 DESCRIPTION
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For all of the functions below that set the supported groups there must be at
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least one group in the list. A number of these functions identify groups via a
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unique integer NID value. However, support for some groups may be added by
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external providers. In this case there will be no NID assigned for the group.
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When setting such groups applications should use the "list" form of these
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functions (i.e. SSL_CTX_set1_groups_list() and SSL_set1_groups_list).
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SSL_CTX_set1_groups() sets the supported groups for B<ctx> to B<glistlen>
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groups in the array B<glist>. The array consist of all NIDs of groups in
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preference order. For a TLS client the groups are used directly in the
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supported groups extension. For a TLS server the groups are used to
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determine the set of shared groups. Currently supported groups for
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B<TLSv1.3> are B<NID_X9_62_prime256v1>, B<NID_secp384r1>, B<NID_secp521r1>,
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B<NID_X25519>, B<NID_X448>, B<NID_ffdhe2048>, B<NID_ffdhe3072>,
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B<NID_ffdhe4096>, B<NID_ffdhe6144> and B<NID_ffdhe8192>.
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SSL_CTX_set1_groups_list() sets the supported groups for B<ctx> to
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string B<list>. The string is a colon separated list of group NIDs or
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names, for example "P-521:P-384:P-256:X25519:ffdhe2048". Currently supported
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groups for B<TLSv1.3> are B<P-256>, B<P-384>, B<P-521>, B<X25519>, B<X448>,
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B<ffdhe2048>, B<ffdhe3072>, B<ffdhe4096>, B<ffdhe6144>, B<ffdhe8192>. Support
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for other groups may be added by external providers.
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SSL_set1_groups() and SSL_set1_groups_list() are similar except they set
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supported groups for the SSL structure B<ssl>.
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SSL_get1_groups() returns the set of supported groups sent by a client
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in the supported groups extension. It returns the total number of
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supported groups. The B<groups> parameter can be B<NULL> to simply
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return the number of groups for memory allocation purposes. The
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B<groups> array is in the form of a set of group NIDs in preference
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order. It can return zero if the client did not send a supported groups
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extension. If a supported group NID is unknown then the value is set to the
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bitwise OR of TLSEXT_nid_unknown (0x1000000) and the id of the group.
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SSL_get_shared_group() returns the NID of the shared group B<n> for a
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server-side SSL B<ssl>. If B<n> is -1 then the total number of shared groups is
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returned, which may be zero. Other than for diagnostic purposes,
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most applications will only be interested in the first shared group
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so B<n> is normally set to zero. If the value B<n> is out of range,
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NID_undef is returned. If the NID for the shared group is unknown then the value
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is set to the bitwise OR of TLSEXT_nid_unknown (0x1000000) and the id of the
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group.
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SSL_get_negotiated_group() returns the NID of the negotiated group used for
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the handshake key exchange process. For TLSv1.3 connections this typically
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reflects the state of the current connection, though in the case of PSK-only
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resumption, the returned value will be from a previous connection. For earlier
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TLS versions, when a session has been resumed, it always reflects the group
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used for key exchange during the initial handshake (otherwise it is from the
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current, non-resumption, connection). This can be called by either client or
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server. If the NID for the shared group is unknown then the value is set to the
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bitwise OR of TLSEXT_nid_unknown (0x1000000) and the id of the group.
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All these functions are implemented as macros.
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The curve functions are synonyms for the equivalently named group functions and
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are identical in every respect. They exist because, prior to TLS1.3, there was
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only the concept of supported curves. In TLS1.3 this was renamed to supported
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groups, and extended to include Diffie Hellman groups. The group functions
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should be used in preference.
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=head1 NOTES
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If an application wishes to make use of several of these functions for
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configuration purposes either on a command line or in a file it should
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consider using the SSL_CONF interface instead of manually parsing options.
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=head1 RETURN VALUES
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SSL_CTX_set1_groups(), SSL_CTX_set1_groups_list(), SSL_set1_groups() and
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SSL_set1_groups_list(), return 1 for success and 0 for failure.
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SSL_get1_groups() returns the number of groups, which may be zero.
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SSL_get_shared_group() returns the NID of shared group B<n> or NID_undef if there
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is no shared group B<n>; or the total number of shared groups if B<n>
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is -1.
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When called on a client B<ssl>, SSL_get_shared_group() has no meaning and
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returns -1.
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SSL_get_negotiated_group() returns the NID of the negotiated group used for
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key exchange, or NID_undef if there was no negotiated group.
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=head1 SEE ALSO
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L<ssl(7)>,
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L<SSL_CTX_add_extra_chain_cert(3)>
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=head1 HISTORY
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The curve functions were added in OpenSSL 1.0.2. The equivalent group
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functions were added in OpenSSL 1.1.1. The SSL_get_negotiated_group() function
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was added in OpenSSL 3.0.0.
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=head1 COPYRIGHT
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Copyright 2013-2020 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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