Certificate Fingerprint (SHA-256) Regex for JavaScript

What this pattern does

This page provides a well-structured, multi-part regular expression for matching certificate fingerprint (sha-256), ported and verified for JavaScript. 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 JavaScript project — whether you're validating in an Express middleware, a Next.js API route, or a client-side form.

Javascript Implementation

// Certificate Fingerprint (SHA-256)
// ReDoS-safe | RegexVault — Security > Certificates & PKI

const certificateFingerprintSha256Regex = /^[0-9A-F]{2}(?::[0-9A-F]{2}){31}$/i;

function validateCertificateFingerprintSha256(input: string): boolean {
  return certificateFingerprintSha256Regex.test(input);
}

// Example
console.log(validateCertificateFingerprintSha256("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")); // 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 JavaScript developers because especially critical in long-running Node.js event loops where a ReDoS vulnerability can block the entire process. 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.