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Title "SSL_CTX_set1_curves 3"
way too many mistakes in technical documents.
\fBSSL_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 \fBTLSv1.3 are NID_X9_62_prime256v1, NID_secp384r1, NID_secp521r1, \fBNID_X25519, NID_X448, NID_ffdhe2048, NID_ffdhe3072, \fBNID_ffdhe4096, NID_ffdhe6144 and NID_ffdhe8192.
\fBSSL_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, \fBffdhe2048, ffdhe3072, ffdhe4096, ffdhe6144, ffdhe8192. Support for other groups may be added by external providers.
\fBSSL_set1_groups() and SSL_set1_groups_list() are similar except they set supported groups for the SSL structure ssl.
\fBSSL_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 \fBgroups 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.
\fBSSL_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.
\fBSSL_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.
\fBSSL_get1_groups() returns the number of groups, which may be zero.
\fBSSL_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.
\fBSSL_get_negotiated_group() returns the NID of the negotiated group used for key exchange, or NID_undef if there was no negotiated group.
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>.