From 9a47d1320e070ee77e05070632a0521859ed94f4 Mon Sep 17 00:00:00 2001
From: Jon Chambers <jon.chambers@gmail.com>
Date: Mon, 17 Aug 2026 16:32:15 -0400
Subject: [PATCH] Use a more "constant-time" approach for validating one-time
 passwords

---
 .../java/com/eatthepath/otp/HmacOneTimePasswordGenerator.java | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/main/java/com/eatthepath/otp/HmacOneTimePasswordGenerator.java b/src/main/java/com/eatthepath/otp/HmacOneTimePasswordGenerator.java
index 94d2635..16abf3d 100644
--- a/src/main/java/com/eatthepath/otp/HmacOneTimePasswordGenerator.java
+++ b/src/main/java/com/eatthepath/otp/HmacOneTimePasswordGenerator.java
@@ -275,7 +275,9 @@ public boolean validateOneTimePassword(final SecretKey key, final long counter,
      * @see <a href="https://datatracker.ietf.org/doc/html/rfc4226#section-7">HOTP: An HMAC-Based One-Time Password Algorithm (RFC 4226) - Security Requirements</a>
      */
     public boolean validateOneTimePassword(final SecretKey key, final long counter, final int oneTimePassword) throws InvalidKeyException {
-        return generateOneTimePassword(key, counter) == oneTimePassword;
+        // This looks a little goofy, but the idea is to ward off any CPU-specific optimizations that might make
+        // direct integer comparison a not-constant-time operation
+        return (generateOneTimePassword(key, counter) ^ oneTimePassword) == 0;
     }
 
     /**