1 files changed, 21 insertions, 2 deletions

diff --git a/mac.c b/mac.c
index f63fbff09..6b12cd197 100644
--- a/mac.c
+++ b/mac.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: mac.c,v 1.32 2015/01/15 18:32:54 naddy Exp $ */
+/* $OpenBSD: mac.c,v 1.33 2016/07/08 03:44:42 djm Exp $ */
 /*
  * Copyright (c) 2001 Markus Friedl.  All rights reserved.
  *
@@ -167,7 +167,8 @@ mac_init(struct sshmac *mac)
 }
 
 int
-mac_compute(struct sshmac *mac, u_int32_t seqno, const u_char *data, int datalen,
+mac_compute(struct sshmac *mac, u_int32_t seqno,
+    const u_char *data, int datalen,
     u_char *digest, size_t dlen)
 {
         static union {
@@ -211,6 +212,24 @@ mac_compute(struct sshmac *mac, u_int32_t seqno, const u_char *data, int datalen
         return 0;
 }
 
+int
+mac_check(struct sshmac *mac, u_int32_t seqno,
+    const u_char *data, size_t dlen,
+    const u_char *theirmac, size_t mlen)
+{
+        u_char ourmac[SSH_DIGEST_MAX_LENGTH];
+        int r;
+
+        if (mac->mac_len > mlen)
+                return SSH_ERR_INVALID_ARGUMENT;
+        if ((r = mac_compute(mac, seqno, data, dlen,
+            ourmac, sizeof(ourmac))) != 0)
+                return r;
+        if (timingsafe_bcmp(ourmac, theirmac, mac->mac_len) != 0)
+                return SSH_ERR_MAC_INVALID;
+        return 0;
+}
+
 void
 mac_clear(struct sshmac *mac)
 {