Encrypt/Decrypt String Kotlin

Issue

I've created this two extensions in Kotlin to Encrypt/Decrypt strings:

fun String.encrypt(seed : String): String {
    val keyGenerator = KeyGenerator.getInstance("AES")
    val secureRandom = SecureRandom.getInstance("SHA1PRNG")
    secureRandom.setSeed(seed.toByteArray())

    keyGenerator.init(128, secureRandom)
    val skey = keyGenerator.generateKey()
    val rawKey : ByteArray = skey.encoded

    val skeySpec = SecretKeySpec(rawKey, "AES")
    val cipher = Cipher.getInstance("AES/CBC/PKCS5Padding")
    cipher.init(Cipher.ENCRYPT_MODE, skeySpec)
    val byteArray = cipher.doFinal(this.toByteArray())

    return byteArray.toString()
}

fun String.decrypt(seed : String): String {
    val keyGenerator = KeyGenerator.getInstance("AES")
    val secureRandom = SecureRandom.getInstance("SHA1PRNG")
    secureRandom.setSeed(seed.toByteArray())

    keyGenerator.init(128, secureRandom)
    val skey = keyGenerator.generateKey()
    val rawKey : ByteArray = skey.encoded

    val skeySpec = SecretKeySpec(rawKey, "AES")
    val cipher = Cipher.getInstance("AES/CBC/PKCS5Padding")
    cipher.init(Cipher.DECRYPT_MODE, skeySpec)
    val byteArray = cipher.doFinal(this.toByteArray())

    return byteArray.toString()
}

for some reason I'm getting the following exception:

javax.crypto.IllegalBlockSizeException: last block incomplete in decryption

What I'm doing wrong?

Solution

To encode your ciphertext use base 64 or hexadecimals. The Java API contains a Base64 class, so you're probably best off using that.

byte[]#toString doesn't do what you expect it to do; it simply returns a representation of the byte array reference, not the contents of the byte array.

---

Besides that:

• don't use SecureRandom to derive a key, try and lookup PBKDF2;
• explicitly use a mode of operation such as "AES/GCM/NoPadding";
• use a unique IV, and a random IV if you decide to use CBC (usually insecure);
• don't use toByteArray without explicitly selecting a character encoding for the message.

Answered By - Maarten Bodewes