const { subtle } = crypto

const iterations = 1000;

const dec = async () => {
  try {
    let password = await prompt('password for decrypt: ')
    password = password.trim()

    let data = await prompt('encrypted base64 data: ')
    data = data.trim()

    const encoder = new TextEncoder()

    const keyMaterial = await subtle.importKey(
      'raw',
      encoder.encode(password),
      'PBKDF2',
      false,
      ['deriveKey', 'deriveBits']
    )

    const salt = encoder.encode(password)

    const bits = await subtle.deriveBits({
      name: 'PBKDF2',
      hash: 'SHA-512',
      salt,
      iterations
    }, keyMaterial, 256)

    const key = await subtle.deriveKey(
      {
        name: 'PBKDF2',
        hash: 'SHA-512',
        salt,
        iterations
      },
      keyMaterial,
      {
        name: 'AES-GCM',
        length: 256,
      },
      true,
      ['encrypt', 'decrypt']
    )

    const ciphertext = Uint8Array.from(atob(data), c => c.charCodeAt(0))

    const decrypted = await subtle.decrypt(
      {
        name: 'AES-GCM',
        iv: bits
      },
      key,
      ciphertext
    )

    const decoder = new TextDecoder()

    console.log('original: ', decoder.decode(decrypted))
  } catch (err) {
    console.error('Question rejected', err)
  }
}