From 8e9466e306119af3b77e7e623ce71988d2b7f86f Mon Sep 17 00:00:00 2001
From: Rich Trott <rtrott@gmail.com>
Date: Fri, 30 Apr 2021 12:00:40 -0700
Subject: [PATCH] wip: add HMAC to crypto.timingSafeEqual()

Refs: https://github.com/nodejs/node/issues/38226
---
 src/crypto/crypto_timing.cc                   | 42 ++++++++++++++++++-
 ...est-crypto-timing-safe-equal-benchmarks.js |  2 +-
 2 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/src/crypto/crypto_timing.cc b/src/crypto/crypto_timing.cc
index 0a9b167223b846..9fc0fe3eb3a4c9 100644
--- a/src/crypto/crypto_timing.cc
+++ b/src/crypto/crypto_timing.cc
@@ -6,6 +6,8 @@
 #include "node.h"
 
 #include <openssl/crypto.h>
+#include <openssl/hmac.h>
+#include <openssl/sha.h>
 
 namespace node {
 
@@ -42,8 +44,46 @@ void TimingSafeEqual(const FunctionCallbackInfo<Value>& args) {
     return;
   }
 
+  uint16_t bufKey[8];
+  CHECK(crypto::EntropySource(reinterpret_cast<unsigned char*>(bufKey),
+                              sizeof(bufKey)));
+  int keySize = 256;
+  char key[keySize];
+  snprintf(key, sizeof(key), "%04x%04x%04x%04x%04x%04x%04x%04x",
+           bufKey[0],
+           bufKey[1],
+           bufKey[2],
+           bufKey[3],
+           bufKey[4],
+           bufKey[5],
+           bufKey[6],
+           bufKey[7]);
+               
+  std::array<unsigned char, EVP_MAX_MD_SIZE> hash1;
+  std::array<unsigned char, EVP_MAX_MD_SIZE> hash2;
+  unsigned int hash1Len;
+  unsigned int hash2Len;
+
+  HMAC(EVP_sha256(),
+       key,
+       keySize,
+       reinterpret_cast<unsigned char const*>(buf1.data()),
+       static_cast<int>(buf1.size()),
+       hash1.data(),
+       &hash1Len);
+
+  HMAC(EVP_sha256(),
+       key,
+       keySize,
+       reinterpret_cast<unsigned char const*>(buf2.data()),
+       static_cast<int>(buf2.size()),
+       hash2.data(),
+       &hash2Len);
+
+  assert(hash1Len == hash2Len);
+
   return args.GetReturnValue().Set(
-      CRYPTO_memcmp(buf1.data(), buf2.data(), buf1.size()) == 0);
+      CRYPTO_memcmp(hash1.data(), hash2.data(), hash1Len) == 0);
 }
 
 void Initialize(Environment* env, Local<Object> target) {
diff --git a/test/pummel/test-crypto-timing-safe-equal-benchmarks.js b/test/pummel/test-crypto-timing-safe-equal-benchmarks.js
index b649b071e1e49d..3c6e31e8294cc8 100644
--- a/test/pummel/test-crypto-timing-safe-equal-benchmarks.js
+++ b/test/pummel/test-crypto-timing-safe-equal-benchmarks.js
@@ -111,7 +111,7 @@ assert(
   `timingSafeEqual should not leak information from its execution time (t=${t})`
 );
 
-// As a sanity check to make sure the statistical tests are working, run the
+// As a coherence check to make sure the statistical tests are working, run the
 // same benchmarks again, this time with an unsafe comparison function. In this
 // case the t-value should be above the threshold.
 const unsafeCompare = (bufA, bufB) => bufA.equals(bufB);