Certificate Decoder - Decode X.509 PEM Certificates Online

// Certificate Decoder - JavaScript Implementation
// Uses Web Crypto API for fingerprint computation

/**
 * Extract the DER bytes from a PEM string
 * @param {string} pem - PEM-encoded certificate
 * @returns {ArrayBuffer} DER-encoded certificate bytes
 */
function pemToDer(pem) {
  const base64 = pem
    .replace(/-----BEGIN CERTIFICATE-----/g, '')
    .replace(/-----END CERTIFICATE-----/g, '')
    .replace(/\s/g, '');
  const binary = atob(base64);
  const bytes = new Uint8Array(binary.length);
  for (let i = 0; i < binary.length; i++) {
    bytes[i] = binary.charCodeAt(i);
  }
  return bytes.buffer;
}

/**
 * Parse multiple certificates from a PEM chain
 * @param {string} pemText - PEM text (may contain multiple certificates)
 * @returns {string[]} Array of individual PEM certificate strings
 */
function extractPemBlocks(pemText) {
  const regex = /-----BEGIN CERTIFICATE-----[\s\S]*?-----END CERTIFICATE-----/g;
  return pemText.match(regex) || [];
}

/**
 * Compute SHA-256 fingerprint of a DER-encoded certificate
 * @param {ArrayBuffer} derBytes - DER-encoded certificate
 * @returns {Promise<string>} Colon-separated hex fingerprint
 */
async function computeSha256Fingerprint(derBytes) {
  const hashBuffer = await crypto.subtle.digest('SHA-256', derBytes);
  const hashArray = Array.from(new Uint8Array(hashBuffer));
  return hashArray
    .map(b => b.toString(16).padStart(2, '0').toUpperCase())
    .join(':');
}

// Usage with @peculiar/x509:
// import { X509Certificate } from '@peculiar/x509';
// const cert = new X509Certificate(pem);
// console.log('Subject:', cert.subject);
// console.log('Issuer:', cert.issuer);