web crypto for AES-CBC

aes.js

const atos = a =>
  Array.from(a)
    .map(c => String.fromCodePoint(c))
    .join('')

const stoa = s => Array.from(s).map(c => c.codePointAt())

const createAes = (keyString, ivString) => {
  const keyUtf8 = new TextEncoder().encode(keyString)
  const ivUtf8 = new TextEncoder().encode(ivString)
  const alg = {name: 'AES-CBC', iv: ivUtf8}
  let key
  const getKey = () => {
    if (!key) {
      key = crypto.subtle.importKey('raw', keyUtf8, alg, false, [
        'encrypt',
        'decrypt',
      ])
    }
    return key
  }

  const encrypt = async (input, to = 'arraybuffer') => {
    const data = ArrayBuffer.isView(input)
      ? input
      : new TextEncoder().encode(input)
    const ab = await crypto.subtle.encrypt(alg, await getKey(), data)
    if (to === 'string') {
      return atos(new Uint8Array(ab))
    } else if (to === 'base64') {
      return btoa(atos(new Uint8Array(ab)))
    }
    return ab
  }

  const decrypt = async (encrypted, to = 'arraybuffer') => {
    const ab = await crypto.subtle.decrypt(alg, await getKey(), encrypted)
    if (to === 'string') {
      return new TextDecoder().decode(ab)
    }
    return ab
  }

  const decryptBase64 = (b64String, to) => {
    return decrypt(new Uint8Array(stoa(atob(b64String))), to)
  }

  const decryptString = (string, to) => {
    return decrypt(new Uint8Array(stoa(string)), to)
  }

  return {encrypt, decrypt, decryptBase64, decryptString}
}

exports.createAes = createAes

demo.js

const mainB64 = async () => {
  const aes = createAes(KEY, IV)
  
  const ctB64 = await aes.encrypt(message, 'base64')
  console.info('encrypted:b64', ctB64)
  
  const pt = await aes.decryptBase64(ctB64, 'string')
  console.assert(pt === message)
}

const main = async () => {
  const aes = createAes(KEY, IV)
  
  const ct = await aes.encrypt(message, 'string')
  console.info('encrypted:string', ct)
  
  const pt = await aes.decryptString(ct, 'string')
  console.info('decrypted:string', pt)
  console.assert(pt === message)
}

mainAb()
mainB64()