SHA-3 / Keccak Hash (256 and 512) Regex for PHP

What this pattern does

This page provides a well-structured, multi-part regular expression for matching sha-3 / keccak hash (256 and 512), ported and verified for PHP. In security-sensitive code, using an unverified regex can open the door to both false positives and denial-of-service attacks. The snippet below is ready to drop into your PHP project — whether you're validating in a Laravel validator, a WordPress plugin, or a standalone PHP script.

Php Implementation

<?php
// SHA-3 / Keccak Hash (256 and 512)
// ReDoS-safe | RegexVault — Security > Password Formats

define('SHA3_KECCAK_HASH_256_AND_512_PATTERN', '/^[a-f0-9]{64}$|^[a-f0-9]{128}$/');

function validate_sha3_keccak_hash_256_and_512(string $input): bool {
    return (bool) preg_match(SHA3_KECCAK_HASH_256_AND_512_PATTERN, $input);
}

// Example
var_dump(validate_sha3_keccak_hash_256_and_512("a7ffc6f8bf1ed76651c14756a061d662f580ff4de43b49fa82d80a4b80f8434a")); // bool(true)

Test Cases

When to use this pattern

This pattern is drawn from the Security > Password Formats category and carries a ReDoS-safe certification. That matters for PHP developers because especially relevant in PHP where PCRE backtracking limits can trigger silent failures on malicious input. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.

Common Pitfalls

Technical Notes

SHA-3 (Standardized 2015, FIPS 202) uses a completely different internal construction (Keccak sponge) from SHA-2. Resistant to length-extension attacks that affect SHA-2. Note: SHA3-256 and SHA-256 produce the same output length (64 hex) — distinguish by context/system documentation.