SSH Private Key (OpenSSH Format) Regex for PHP

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching ssh private key (openssh format), 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
// SSH Private Key (OpenSSH Format)
// ReDoS-safe | RegexVault — Security > Certificates & PKI

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

function validate_ssh_private_key_openssh_format(string $input): bool {
    return (bool) preg_match(SSH_PRIVATE_KEY_OPENSSH_FORMAT_PATTERN, $input);
}

// Example
var_dump(validate_ssh_private_key_openssh_format("-----BEGIN OPENSSH PRIVATE KEY-----
b3BlbnNzaC1rZXktdjEAAAAAAAAA
-----END OPENSSH 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

OpenSSH private key format (openssh-key-v1) is the default since OpenSSH 6.5 (2014). Unlike PEM RSA keys, this format includes key type metadata and may be passphrase-protected. The base64 payload includes the key type, public key, and encrypted private key.