TFyWa9G9

1package com.practicingtechie
2
3// implement AEAD with AES + GCM
4object AeadHelper {
5  import javax.crypto._
6  import javax.crypto.spec.{GCMParameterSpec, SecretKeySpec}
7  import java.security._
8  import java.util.Base64
9
10  val AesKeySize = 256
11  val IvSize = 96
12  val TagBitLength = 128
13  val AlgoTransformationString = "AES/GCM/PKCS5Padding"
14
15  val SecretKeyString = "<base64 encoded key here>"
16  val SecretKey = new SecretKeySpec(Base64.getDecoder.decode(SecretKeyString), "AES")
17  val secRandom = new SecureRandom
18
19
20  def generateKey = {
21    val keygen = KeyGenerator.getInstance("AES")
22    keygen.init(AesKeySize)
23    val key = keygen.generateKey
24    println(s"key: ${Base64.getEncoder.encodeToString(key.getEncoded)}")
25    key
26  }
27
28  def encrypt(plainText: Array[Byte], aad: Array[Byte]) = {
29    def aesEncrypt(plainText: Array[Byte], aesKey: SecretKey, gcmParamSpec: GCMParameterSpec, aadData: Array[Byte]) = {
30      val c = Cipher.getInstance(AlgoTransformationString)
31      c.init(Cipher.ENCRYPT_MODE, aesKey, gcmParamSpec, new SecureRandom)
32      c.updateAAD(aadData)
33      c.doFinal(plainText)
34    }
35    val iv = new Array[Byte](IvSize)
36    secRandom.nextBytes(iv)
37    val gcmParamSpec = new GCMParameterSpec(TagBitLength, iv)
38    val cipherText = aesEncrypt(plainText, SecretKey,  gcmParamSpec, aad)
39    val buf = new Array[Byte](IvSize + cipherText.size)
40    System.arraycopy(iv, 0, buf, 0, IvSize)
41    System.arraycopy(cipherText, 0, buf, IvSize, cipherText.size)
42    buf
43  }
44
45  def decrypt(message: Array[Byte], aad: Array[Byte]) = {
46    def aesDecrypt(cipherText: Array[Byte], aesKey: SecretKey, gcmParamSpec: GCMParameterSpec, aadData: Array[Byte]): Array[Byte] = {
47      val c = Cipher.getInstance(AlgoTransformationString)
48      c.init(Cipher.DECRYPT_MODE, aesKey, gcmParamSpec, new SecureRandom)
49      c.updateAAD(aadData)
50      c.doFinal(cipherText)
51    }
52    val cipherTextLen = message.size - IvSize
53    val gcmParamSpec = new GCMParameterSpec(TagBitLength, message, 0, IvSize)
54    val cipherText = new Array[Byte](cipherTextLen)
55    System.arraycopy(message, IvSize, cipherText, 0, cipherTextLen)
56    aesDecrypt(cipherText, SecretKey, gcmParamSpec, aad)
57  }
58
59  def runEncryptDecrypt(plainText: String, aad: String) = {
60    val cipherText = encrypt(plainText.getBytes, aad.getBytes)
61
62    println(s"cipher text: '${Base64.getEncoder.encodeToString(cipherText)}'")
63
64    val decryptedText = decrypt(cipherText, aad.getBytes)
65    println(s"decrypted text '${new String(decryptedText)}'")
66  }
67
68}