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SSL_CTX_SET1_GROUPS(3) Library Functions Manual SSL_CTX_SET1_GROUPS(3)

SSL_CTX_set1_groups, SSL_CTX_set1_groups_list, SSL_set1_groups, SSL_set1_groups_list, SSL_CTX_set1_curves, SSL_CTX_set1_curves_list, SSL_set1_curves, SSL_set1_curves_list
choose supported EC groups

#include <openssl/ssl.h>
SSL_CTX_set1_groups(SSL_CTX *ctx, const int *glist, size_t glistlen);
SSL_CTX_set1_groups_list(SSL_CTX *ctx, const char *list);
SSL_set1_groups(SSL *ssl, const int *glist, size_t glistlen);
SSL_set1_groups_list(SSL *ssl, const char *list);
SSL_CTX_set1_curves(SSL_CTX *ctx, const int *clist, size_t clistlen);
SSL_CTX_set1_curves_list(SSL_CTX *ctx, const char *list);
SSL_set1_curves(SSL *ssl, const int *clist, size_t clistlen);
SSL_set1_curves_list(SSL *ssl, const char *list);

SSL_CTX_set1_groups() sets the supported groups for ctx to the glistlen groups in the array glist. The array consists of group NIDs 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 the list represented as 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 that they set supported groups for the SSL structure ssl only.
The curve functions are deprecated synonyms for the equivalently named group functions and are identical in every respect except that they are implemented as macros. 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.
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.

All these functions return 1 for success or 0 for failure.

ssl(3), SSL_CTX_add_extra_chain_cert(3), SSL_CTX_set_cipher_list(3), SSL_CTX_set_options(3), SSL_new(3)

The curve functions first appeared in OpenSSL 1.0.2 and the group functions in OpenSSL 1.1.1. Both have been available since OpenBSD 6.1.
August 19, 2017 OpenBSD-current