CODEWITHSUNDEEP
javascriptangulartypescriptencryptionaes
Usman Afzal
Usman Afzal

Reputation: 476

First 16 Characters of decrypted string are garbage

I have a scenario where data is encrypted from the API and then decrypted in typescript. I have used cryptoJS for decryption in typescript. Following is my decryption code:

decrypt(source: string, iv: string): string {
var key = environment.config.KEY_PAYMENT.substring(0, 32);
const keyValue = CryptoJS.enc.Utf8.parse(key);
const ivValue = CryptoJS.enc.Utf8.parse(iv);
const plainText = CryptoJS.AES.decrypt(source, keyValue, {
  keySize: 16,
  iv: ivValue,
  mode: CryptoJS.mode.CBC,
  padding: CryptoJS.pad.Pkcs7
});
return CryptoJS.enc.Latin1.stringify(plainText);

} The IV and key value are provided. I have a Java Sample Code that is being used for decryption for mobile application which is working as expected. Code sample is here:

fun decrypt(
    source: ByteArray,
    key: String,
    iv: ByteArray
  ): ByteArray {
    val cipher = Cipher.getInstance("AES/CBC/PKCS5Padding")
    cipher.init(Cipher.DECRYPT_MODE, makeKey(key), makeIv(iv))
    return cipher.doFinal(source)
  }

  private fun makeIv(iv: ByteArray): AlgorithmParameterSpec {
    return IvParameterSpec(iv)
  }

  private fun makeKey(baseKey: String): Key? {
    return try {
      val key = baseKey.substring(0, 32)
          .toByteArray(charset("UTF-8"))
      SecretKeySpec(key, "AES")
    } catch (e: UnsupportedEncodingException) {
      null
    }
  }

Sample Output:

ªîto7“ßH«3©@V¨sr","paymentType":"credit_card",...

The first 16 characters are garbage and rest of the string is decrypted successfully. I am stuck here.

Upvotes: 0

Views: 815

Answers (2)

Usman Afzal
Usman Afzal

Reputation: 476

This worked from me:

  decrypt(source: string, iv: string) {
    debugger;
    var key = environment.config.KEY_PAYMENT.substring(0, 32);
    const keyValue = CryptoJS.enc.Utf8.parse(key);
    const ivVal = CryptoJS.enc.Base64.parse(iv);//This Line
    const plainText = CryptoJS.AES.decrypt(source, keyValue, { iv: ivVal });
    return CryptoJS.enc.Latin1.stringify(plainText);
  }

The crypto JS has it's own base64 encoding function that returned the correct result.

Upvotes: 1

poncho
poncho

Reputation: 206

"First 16 characters wrong; everything else looks good" typically means you got the IV wrong.

Everything in the code you provided looks legit; I suspect that the caller to decrypt is not passing the correct IV value.

Upvotes: 2

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