PEM Private Key Block Regex for JavaScript

What this pattern does

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

// PEM Private Key Block
// ReDoS-safe | RegexVault — Security > Certificates & PKI

const pemPrivateKeyBlockRegex = /-----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 validatePemPrivateKeyBlock(input: string): boolean {
  return pemPrivateKeyBlockRegex.test(input);
}

// Example
console.log(validatePemPrivateKeyBlock("-----BEGIN PRIVATE KEY-----
MIIEvAIBADANBgk=
-----END PRIVATE KEY-----")); // 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

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.