session: add getter for kexalgo

Signed-off-by: Jon Simons <jon@jonsimons.org>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>

include/libssh/libssh.h

@@ -658,6 +658,7 @@ LIBSSH_API int ssh_event_remove_session(ssh_event event, ssh_session session);
 LIBSSH_API void ssh_event_free(ssh_event event);
 LIBSSH_API const char* ssh_get_clientbanner(ssh_session session);
 LIBSSH_API const char* ssh_get_serverbanner(ssh_session session);
+LIBSSH_API const char* ssh_get_kex_algo(ssh_session session);
 LIBSSH_API const char* ssh_get_cipher_in(ssh_session session);
 LIBSSH_API const char* ssh_get_cipher_out(ssh_session session);
 LIBSSH_API const char* ssh_get_hmac_in(ssh_session session);

src/session.c

@@ -314,6 +314,35 @@ const char* ssh_get_serverbanner(ssh_session session) {
 	return session->serverbanner;
 }
 
+/**
+ * @brief get the name of the current key exchange algorithm.
+ *
+ * @param[in] session   The SSH session
+ *
+ * @return Returns the key exchange algorithm string or NULL.
+ */
+const char* ssh_get_kex_algo(ssh_session session) {
+    if ((session == NULL) ||
+        (session->current_crypto == NULL)) {
+        return NULL;
+    }
+
+    switch (session->current_crypto->kex_type) {
+        case SSH_KEX_DH_GROUP1_SHA1:
+            return "diffie-hellman-group1-sha1";
+        case SSH_KEX_DH_GROUP14_SHA1:
+            return "diffie-hellman-group14-sha1";
+        case SSH_KEX_ECDH_SHA2_NISTP256:
+            return "ecdh-sha2-nistp256";
+        case SSH_KEX_CURVE25519_SHA256_LIBSSH_ORG:
+            return "curve25519-sha256@libssh.org";
+        default:
+            break;
+    }
+
+    return NULL;
+}
+
 /**
  * @brief get the name of the input cipher for the given session.
  *