Encrypt a message, image, or file with a password. The result is a standalone HTML file that anyone can decrypt in their browser — no tools or accounts needed.

All encryption happens locally in your browser using the 

. Your secret never leaves your computer.

https://mprimi.github.io/portable-secret/

return render(() => <PortableSecretCreator />);

// Crypto constants
const BLOCK_SIZE = 16;
const SALT_SIZE = 32;
const ITERATIONS = 1000000;
const KEY_SIZE = 256;

function toHex(buffer) {
  return Array.from(new Uint8Array(buffer))
    .map(b => b.toString(16).padStart(2, '0'))
    .join('');
}

function pkcs7Pad(data) {
  const padAmount = BLOCK_SIZE - (data.length % BLOCK_SIZE);
  const padded = new Uint8Array(data.length + padAmount);
  padded.set(data);
  padded.fill(padAmount, data.length);
  return padded;
}

function generateSalt() {
  return crypto.getRandomValues(new Uint8Array(SALT_SIZE));
}

function generateIV() {
  return crypto.getRandomValues(new Uint8Array(BLOCK_SIZE));
}

async function encryptSecret(password, plainBytes, secretType, fileExtension, opts = {}) {
  const enc = new TextEncoder();
  const salt = opts.salt || generateSalt();
  const iv = opts.iv || generateIV();
  const iterations = opts.iterations || ITERATIONS;

  const keyMaterial = await crypto.subtle.importKey(
    'raw', enc.encode(password), 'PBKDF2', false, ['deriveKey']
  );

  const key = await crypto.subtle.deriveKey(
    { name: 'PBKDF2', salt, iterations, hash: 'SHA-256' },
    keyMaterial,
    { name: 'AES-GCM', length: KEY_SIZE },
    false,
    ['encrypt']
  );

  const padded = pkcs7Pad(plainBytes);
  const ciphertext = await crypto.subtle.encrypt(
    { name: 'AES-GCM', iv },
    key,
    padded
  );

  return {
    salt: toHex(salt),
    iv: toHex(iv),
    iterations,
    ciphertext: toHex(ciphertext),
    secretType,
    fileExtension: fileExtension || '',
  };
}

return { encryptSecret, toHex, generateSalt, generateIV, ITERATIONS, SALT_SIZE, BLOCK_SIZE };

Portable Secret

Portable Secret Creator

Appendix