PEM Certificate Block Regex for Python

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching pem certificate block, 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

# PEM Certificate Block
# ReDoS-safe | RegexVault — Security > Certificates & PKI

import re

pem_certificate_block_pattern = re.compile(r'-----BEGIN CERTIFICATE-----[\r\n]+(?:[A-Za-z0-9+/=\r\n]{1,80}[\r\n]+)*-----END CERTIFICATE-----')

def validate_pem_certificate_block(value: str) -> bool:
    return bool(pem_certificate_block_pattern.fullmatch(value))

# Example
print(validate_pem_certificate_block("-----BEGIN CERTIFICATE-----
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA
-----END CERTIFICATE-----"))  # 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

PEM format: base64-encoded DER certificate wrapped in BEGIN/END markers. Lines are max 76 characters in the standard. Use for detecting certificates in config files, code, or traffic. Parse with a proper X.509 library to extract subject, issuer, validity, and SANs.