Certificate Fingerprint (SHA-256) Regex for Python

What this pattern does

This page provides a well-structured, multi-part regular expression for matching certificate fingerprint (sha-256), ported and verified for Python. 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 Python project — whether you're validating in a Django view, a FastAPI endpoint, or a standalone data processing script.

Python Implementation

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

import re

certificate_fingerprint_sha256_pattern = re.compile(r'^[0-9A-F]{2}(?::[0-9A-F]{2}){31}$')

def validate_certificate_fingerprint_sha256(value: str) -> bool:
    return bool(certificate_fingerprint_sha256_pattern.fullmatch(value))

# Example
print(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"))  # 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 Python developers because particularly important in Python web servers where CPU-bound regex operations can stall concurrent request handling. 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.