Android Studio Question posted in
The official documentation can be found here.

Android Studio – AES Encryption in Kotlin

The Android docs give the following snippet for how to encrypt a message in AES:

val plaintext: ByteArray = ...
val keygen = KeyGenerator.getInstance("AES")
keygen.init(256)
val key: SecretKey = keygen.generateKey()
val cipher = Cipher.getInstance("AES/CBC/PKCS5PADDING")
cipher.init(Cipher.ENCRYPT_MODE, key)
val ciphertext: ByteArray = cipher.doFinal(plaintext)
val iv: ByteArray = cipher.iv

I get this error when implementing this method:

Unresolved reference: Cipher

So it appears the ‘Cipher’ object isn’t native, however I have no way of knowing how to import it by following the Android docs. How do I set up my project to be able to use ‘Cipher’?

Tags:

2

Answers


  1. 0

    I’m not sure if using that Cipher is necessary, and if the solution I’m providing is the best approach, but I was able to use AES for encryption and decryption using the following code for a text input, means a String:

    ENCRYPTION

    // text

val aesEncrypt: AESEncrypt = AESEncrypt()
val encryptedByteArray = aesEncrypt.encrypt(text)
val baos_text = ByteArrayOutputStream()
val oosText = ObjectOutputStream(baos_text)
oosText.writeObject(encryptedByteArray)
val encryptedText = String(android.util.Base64.encode(baos_text.toByteArray(), android.util.Base64.DEFAULT))

// key

val key = aesEncrypt.mySecretKey
val baos = ByteArrayOutputStream()
val oos = ObjectOutputStream(baos)
oos.writeObject(key)
val keyAsString = String(android.util.Base64.encode(baos.toByteArray(), android.util.Base64.DEFAULT))

// initialisation vector

val iv = aesEncrypt.myInitializationVector
val baosIV = ByteArrayOutputStream()
val oosIV = ObjectOutputStream(baosIV)
oosIV.writeObject(iv)
val initialisationVector = String(android.util.Base64.encode(baosIV.toByteArray(), android.util.Base64.DEFAULT))

    DECRYPTION

    You must save the key, initialisation vector, and the encrypted text in order to decrypt it back.

    val initialisationVector = ... // get from wherever you saved it, local db, firebase...

val bytesIV = android.util.Base64.decode(iv, android.util.Base64.DEFAULT)
val oisIV = ObjectInputStream(ByteArrayInputStream(bytesIV))
val initializationVectorIV = oisIV.readObject() as ByteArray


val encryptedText = ... // get 

val bytesText = android.util.Base64.decode(encryptedText, android.util.Base64.DEFAULT)
val oisText = ObjectInputStream(ByteArrayInputStream(bytesText))
val textByteArray = oisText.readObject() as ByteArray


val key = ... // get your key
val bytesKey = android.util.Base64.decode(key, android.util.Base64.DEFAULT)
val oisKey = ObjectInputStream(ByteArrayInputStream(bytesKey))
val secretKeyObj = oisKey.readObject() as SecretKey


val aesDecrypt = AESDecrypt(secretKeyObj,initializationVectorIV)
val decryptedByteArray = aesDecrypt.decrypt(textByteArray)

val textAfterDecryption = decryptedByteArray.toString(charset("UTF-8"))

    EDIT

    AES helper class:

    import javax.crypto.Cipher
import javax.crypto.KeyGenerator
import javax.crypto.SecretKey

class AESEncrypt {

    var mySecretKey: SecretKey? = null
    var myInitializationVector: ByteArray? = null

    fun encrypt(strToEncrypt: String): ByteArray {

        val plainText = strToEncrypt.toByteArray(Charsets.UTF_8)
        val keygen = KeyGenerator.getInstance("AES")
        keygen.init(256)

        val key = keygen.generateKey()
        mySecretKey = key

        val cipher = Cipher.getInstance("AES/CBC/PKCS5PADDING")
        cipher.init(Cipher.ENCRYPT_MODE, key)
        val cipherText = cipher.doFinal(plainText)
        myInitializationVector = cipher.iv

        return cipherText
    }

}

    AES decrypt helper

    import javax.crypto.Cipher
import javax.crypto.SecretKey
import javax.crypto.spec.IvParameterSpec

class AESDecrypt(private val mySecretKey: SecretKey?, private val initializationVector: ByteArray?) {

    fun decrypt(dataToDecrypt: ByteArray): ByteArray {
        val cipher = Cipher.getInstance("AES/CBC/PKCS5PADDING")
        val ivSpec = IvParameterSpec(initializationVector)
        cipher.init(Cipher.DECRYPT_MODE, mySecretKey, ivSpec)
        val cipherText = cipher.doFinal(dataToDecrypt)

        return cipherText
    }

}

    Do tell if you still need any help 🙂

    Login or Signup to reply.
  2. 0

    javax.crypto.Cipher is part of the JCE and should be available. Does an import javax.crypto.Cipher not work? Then maybe something is wrong with your environment.

    Login or Signup to reply.
Please signup or login to give your own answer.

Back To Top
Search