Compare Secret Values Without Data-Dependent Early Exit
Applications compare secret-derived values in many places: webhook message authentication codes, API tokens, password-reset tokens, signed request authenticators, and other proofs that a caller knows a secret. A normal string or byte comparison may stop as soon as it finds a difference. That is efficient for ordinary data, but it can be the wrong behavior at a security boundary. If the amount of comparison work depends on where two secret values first differ, an observer may be able to learn something from repeated timing measurements. Whether that signal is practically exploitable depends on the surrounding system, noise, protocol, implementation, and attacker access. The defensive decision is still straightforward: when equality of a secret or secret-derived authenticator controls access, use the platform’s dedicated constant-time comparison primitive rather than writing the comparison yourself.