Adding TLS group name retrieval

Function SSL_group_to_name() added, together with documentation and tests.
This now permits displaying names of internal and external
provider-implemented groups.

Partial fix of #13767

Reviewed-by: Tomas Mraz <tmraz@fedoraproject.org>
Reviewed-by: Nicola Tuveri <nic.tuv@gmail.com>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/13785)

1 files changed, 18 insertions, 0 deletions

diff --git a/ssl/s3_lib.c b/ssl/s3_lib.c
index 298efdc1cb..0739bc9082 100644
--- a/ssl/s3_lib.c
+++ b/ssl/s3_lib.c
@@ -4986,3 +4986,21 @@ int ssl_encapsulate(SSL *s, EVP_PKEY *pubkey,
     EVP_PKEY_CTX_free(pctx);
     return rv;
 }
+
+const char *SSL_group_to_name(SSL *s, int nid) {
+    int group_id = 0;
+    const TLS_GROUP_INFO *cinf = NULL;
+
+    /* first convert to real group id for internal and external IDs */
+    if (nid & TLSEXT_nid_unknown)
+        group_id = nid & 0xFFFF;
+    else
+        group_id = tls1_nid2group_id(nid);
+
+    /* then look up */
+    cinf = tls1_group_id_lookup(s->ctx, group_id);
+
+    if (cinf != NULL)
+        return cinf->tlsname;
+    return NULL;
+}