Added checks (in SRP) for A%n==0,1,-1 in server side.

1 files changed, 60 insertions, 21 deletions

diff --git a/libextra/auth_srp.c b/libextra/auth_srp.c
index d0e55d668a..169949b270 100644
--- a/libextra/auth_srp.c
+++ b/libextra/auth_srp.c
@@ -67,6 +67,58 @@ const MOD_AUTH_STRUCT srp_auth_struct = {
 #define V session->key->x
 #define S session->key->KEY
 
+/* Checks if b%n==0 which is a fatal srp error.
+ * Returns a proper error code in that case, and 0 when
+ * all are ok.
+ */
+inline
+static int check_b_mod_n( GNUTLS_MPI b, GNUTLS_MPI n)
+{
+int ret;
+GNUTLS_MPI r = _gnutls_mpi_alloc_like(b);
+
+	_gnutls_mpi_mod( r, b, n);
+	ret = _gnutls_mpi_cmp_ui(r, 0);
+	
+	_gnutls_mpi_release( &r);
+
+	if (ret == 0) {
+		gnutls_assert();
+		return GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER;
+	}
+	
+	return 0;
+}
+
+/* Checks if a%n==0,+1,-1%n which is a fatal srp error.
+ * Returns a proper error code in that case, and 0 when
+ * all are ok.
+ */
+inline
+static int check_a_mod_n( GNUTLS_MPI a, GNUTLS_MPI n)
+{
+int ret;
+GNUTLS_MPI r = _gnutls_mpi_alloc_like(a);
+
+	_gnutls_mpi_mod( r, a, n);
+	ret = _gnutls_mpi_cmp_ui(r, 0);
+	if (ret != 0) ret = _gnutls_mpi_cmp_ui(r, 1);
+	if (ret != 0) {
+		_gnutls_mpi_sub_ui( r, n, 1);
+		ret = _gnutls_mpi_cmp(a, r);
+	}
+	
+	_gnutls_mpi_release( &r);
+
+	if (ret == 0) {
+		gnutls_assert();
+		return GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER;
+	}
+	
+	return 0;
+}
+
+
 /* Send the first key exchange message ( g, n, s) and append the verifier algorithm number 
  * Data is allocated by the caller, and should have data_size size.
  */
@@ -298,6 +350,14 @@ int _gnutls_proc_srp_client_kx(gnutls_session session, opaque * data, size_t _da
 	_gnutls_dump_mpi( "SRP A: ", A);
 	_gnutls_dump_mpi( "SRP B: ", B);
 
+	/* Checks if A % n == 0 or
+	 * A % n == +-1.
+	 */
+	if ( (ret = check_a_mod_n( A, N)) < 0) {
+		gnutls_assert();
+		return ret;
+	}
+
 	/* Start the SRP calculations.
 	 * - Calculate u 
 	 */
@@ -337,27 +397,6 @@ int _gnutls_proc_srp_client_kx(gnutls_session session, opaque * data, size_t _da
 }
 
 
-/* Checks if b%n==0 which is a fatal srp error.
- * Returns a proper error code in that case, and 0 when
- * all are ok.
- */
-static int check_b_mod_n( GNUTLS_MPI b, GNUTLS_MPI n)
-{
-int ret;
-GNUTLS_MPI r = _gnutls_mpi_alloc_like(b);
-
-	_gnutls_mpi_mod( r, b, n);
-	ret = _gnutls_mpi_cmp_ui(r, 0);
-	
-	_gnutls_mpi_release( &r);
-
-	if (ret == 0) {
-		gnutls_assert();
-		return GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER;
-	}
-	
-	return 0;
-}
 
 /* Static parameters according to draft-ietf-tls-srp-05
  */