From 3c4b7ce4825031736a04542103ac490d34f9dae2 Mon Sep 17 00:00:00 2001
From: Kevin Lewi <klewi@fb.com>
Date: Fri, 4 Jun 2021 17:01:49 -0700
Subject: [PATCH] Ensuring mac operations are constant-time

(cherry picked from commit 940d1dcdb29e9de45a5123adab578b3446502b72)
---
 src/key_exchange/tripledh.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/key_exchange/tripledh.rs b/src/key_exchange/tripledh.rs
index 2c504f5..c3b483d 100644
--- a/src/key_exchange/tripledh.rs
+++ b/src/key_exchange/tripledh.rs
@@ -182,7 +182,7 @@ impl<D: Hash, G: Group> KeyExchange<D, G> for TripleDH {
             Hmac::<D>::new_varkey(&km2).map_err(|_| InternalPakeError::HmacError)?;
         server_mac.update(&transcript_hasher.clone().finalize());
 
-        if ke2_message.mac != server_mac.finalize().into_bytes() {
+        if server_mac.verify(&ke2_message.mac).is_err() {
             return Err(ProtocolError::VerificationError(
                 PakeError::KeyExchangeMacValidationError,
             ));
@@ -223,7 +223,7 @@ impl<D: Hash, G: Group> KeyExchange<D, G> for TripleDH {
             Hmac::<D>::new_varkey(&ke2_state.km3).map_err(|_| InternalPakeError::HmacError)?;
         client_mac.update(&ke2_state.hashed_transcript);
 
-        if ke3_message.mac != client_mac.finalize().into_bytes() {
+        if client_mac.verify(&ke3_message.mac).is_err() {
             return Err(ProtocolError::VerificationError(
                 PakeError::KeyExchangeMacValidationError,
             ));