Getting error “wrong final block length” when decrypting AES256 cipher

Question

I\'m facing exactly the same problem mentioned in this thread while encrypting and decrypting using AES.

crypto.js:202
var ret = this._handle.fi

Answer 1

This question is two years old at the time of this writing, but it has quite a few views, so I hope this answer will still prove useful to someone who might come across it.

The problem here is that encryptText works fine, but it's not returning a string. It's returning a Buffer. decryptText is expecting a string, not a Buffer, so it tries to read it as though it were a Buffer and you get the error that you received.

This is a simple fix. We just need to serialise the Buffer to a string when we encrypt text, and deserialise the encrypted string we receive when we decrypt text.

In this example, I use base64 encoding because it is fairly compact when representing binary data.

var config = {
  cryptkey: crypto.createHash('sha256').update('Nixnogen').digest(),
  iv: 'a2xhcgAAAAAAAAAA'
}

function encryptText (text) {
  console.log(config.cryptkey)
  var cipher = crypto.createCipheriv('aes-256-cbc', config.cryptkey, config.iv)
  return Buffer.concat([
    cipher.update(text),
    cipher.final()
  ]).toString('base64') // Output base64 string
}

function decryptText (text) {
  console.log(config.cryptkey)
  if (text === null || typeof text === 'undefined' || text === '') {
    return text
  }
  var decipher = crypto.createDecipheriv('aes-256-cbc', config.cryptkey, config.iv)
  return Buffer.concat([
    decipher.update(text, 'base64'), // Expect `text` to be a base64 string
    decipher.final()
  ]).toString()
}

var encrypted = encryptText('text') // 8xXuS7jLG6crqJFHHB5J5A==
var decrypted = decryptText(encrypted) // text