Certificate Fingerprint (SHA-256) Regex for PHP

What this pattern does

This page provides a well-structured, multi-part regular expression for matching certificate fingerprint (sha-256), 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
// Certificate Fingerprint (SHA-256)
// ReDoS-safe | RegexVault — Security > Certificates & PKI

define('CERTIFICATE_FINGERPRINT_SHA256_PATTERN', '/^[0-9A-F]{2}(?::[0-9A-F]{2}){31}$/');

function validate_certificate_fingerprint_sha256(string $input): bool {
    return (bool) preg_match(CERTIFICATE_FINGERPRINT_SHA256_PATTERN, $input);
}

// Example
var_dump(validate_certificate_fingerprint_sha256("2B:8F:1B:57:33:0D:BB:A2:D0:7A:6C:DD:EC:1A:57:D0:5D:FB:F9:29:35:46:8E:11:33:46:93:D0:F2:CC:54:CA")); // bool(true)

Test Cases

When to use this pattern

This pattern is drawn from the Security > Certificates & PKI 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-256 fingerprint = 256 bits = 32 bytes = 64 hex chars = 32 colon-separated pairs. Used to verify a certificate's identity (pin it) in TLS certificate pinning, SSH known_hosts, and manual certificate verification.