PEM Private Key Block Regex for PHP

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching pem private key block, 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
// PEM Private Key Block
// ReDoS-safe | RegexVault — Security > Certificates & PKI

define('PEM_PRIVATE_KEY_BLOCK_PATTERN', '/-----BEGIN (?:RSA |EC |DSA |OPENSSH )?PRIVATE KEY-----[\r\n]+(?:[A-Za-z0-9+\/=\r\n]{1,80}[\r\n]+)*-----END (?:RSA |EC |DSA |OPENSSH )?PRIVATE KEY-----/');

function validate_pem_private_key_block(string $input): bool {
    return (bool) preg_match(PEM_PRIVATE_KEY_BLOCK_PATTERN, $input);
}

// Example
var_dump(validate_pem_private_key_block("-----BEGIN PRIVATE KEY-----
MIIEvAIBADANBgk=
-----END PRIVATE KEY-----")); // 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

CRITICAL detection pattern. Key type headers: 'PRIVATE KEY' (PKCS#8, unencrypted), 'RSA PRIVATE KEY' (PKCS#1, legacy OpenSSL), 'EC PRIVATE KEY' (SEC1), 'OPENSSH PRIVATE KEY' (SSH private keys). Encrypted private keys have 'ENCRYPTED PRIVATE KEY' header.