Add SSL_get0_group_name() to get name of the group used for KEX

Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/20866)

3 files changed, 27 insertions, 0 deletions

diff --git a/ssl/s3_lib.c b/ssl/s3_lib.c
index 835af33fea..10cff08eae 100644
--- a/ssl/s3_lib.c
+++ b/ssl/s3_lib.c
@@ -5022,6 +5022,22 @@ int ssl_encapsulate(SSL_CONNECTION *s, EVP_PKEY *pubkey,
     return rv;
 }
 
+const char *SSL_get0_group_name(SSL *s)
+{
+    SSL_CONNECTION *sc = SSL_CONNECTION_FROM_SSL(s);
+    unsigned int id;
+
+    if (sc == NULL)
+        return NULL;
+
+    if (SSL_CONNECTION_IS_TLS13(sc) && sc->s3.did_kex)
+        id = sc->s3.group_id;
+    else
+        id = sc->session->kex_group;
+
+    return tls1_group_id2name(s->ctx, id);
+}
+
 const char *SSL_group_to_name(SSL *s, int nid) {
     int group_id = 0;
     const TLS_GROUP_INFO *cinf = NULL;
diff --git a/ssl/ssl_local.h b/ssl/ssl_local.h
index 7ab84acc80..decb02a207 100644
--- a/ssl/ssl_local.h
+++ b/ssl/ssl_local.h
@@ -2767,6 +2767,7 @@ __owur int ssl_check_srvr_ecc_cert_and_alg(X509 *x, SSL_CONNECTION *s);
 SSL_COMP *ssl3_comp_find(STACK_OF(SSL_COMP) *sk, int n);
 
 __owur const TLS_GROUP_INFO *tls1_group_id_lookup(SSL_CTX *ctx, uint16_t curve_id);
+__owur const char *tls1_group_id2name(SSL_CTX *ctx, uint16_t group_id);
 __owur int tls1_group_id2nid(uint16_t group_id, int include_unknown);
 __owur uint16_t tls1_nid2group_id(int nid);
 __owur int tls1_check_group_id(SSL_CONNECTION *s, uint16_t group_id,
diff --git a/ssl/t1_lib.c b/ssl/t1_lib.c
index 189f241f7a..576c7a3271 100644
--- a/ssl/t1_lib.c
+++ b/ssl/t1_lib.c
@@ -755,6 +755,16 @@ const TLS_GROUP_INFO *tls1_group_id_lookup(SSL_CTX *ctx, uint16_t group_id)
     return NULL;
 }
 
+const char *tls1_group_id2name(SSL_CTX *ctx, uint16_t group_id)
+{
+    const TLS_GROUP_INFO *tls_group_info = tls1_group_id_lookup(ctx, group_id);
+
+    if (tls_group_info == NULL)
+        return NULL;
+
+    return tls_group_info->tlsname;
+}
+
 int tls1_group_id2nid(uint16_t group_id, int include_unknown)
 {
     size_t i;