ChaCha20-Poly1305 Java/Kotlin Implementation

ChaCha20-Poly1305.kt

import java.io.File
import java.io.RandomAccessFile
import java.nio.ByteBuffer
import java.security.KeyFactory
import java.security.KeyPairGenerator
import java.security.SecureRandom
import java.security.spec.PKCS8EncodedKeySpec
import java.security.spec.X509EncodedKeySpec
import javax.crypto.Cipher
import javax.crypto.spec.IvParameterSpec
import javax.crypto.spec.SecretKeySpec    

/* OUTPUT: [NB Ciphered][16B signature][12B nounce] */
fun encryptChachaPoly(plain: ByteArray, keyBytes: ByteArray, nonce: ByteArray = generateRandomByteArray(12)): ByteArray {
    val key = SecretKeySpec(keyBytes, "ChaCha20-Poly1305")
    val cipher = Cipher.getInstance("ChaCha20-Poly1305")

    val iv = IvParameterSpec(nonce)
    cipher.init(Cipher.ENCRYPT_MODE, key, iv)
    val ciphered = cipher.doFinal(plain)

    return ByteBuffer.allocate(ciphered.size + 12)
        .put(ciphered)
        .put(nonce)
        .array()
}

/* INPUT:  [NB Ciphered][16B signature][12B nounce] */
fun decryptChachaPoly(ciphered: ByteArray, keyBytes: ByteArray): ByteArray {
    val key = SecretKeySpec(keyBytes, "ChaCha20-Poly1305")
    val buffer: ByteBuffer = ByteBuffer.wrap(ciphered)

    val encryptedText = ByteArray(ciphered.size - 12)
    val nonce = ByteArray(12)
    buffer.get(encryptedText)
    buffer.get(nonce)
    val cipher = Cipher.getInstance("ChaCha20-Poly1305")
    val iv = IvParameterSpec(nonce)
    cipher.init(Cipher.DECRYPT_MODE, key, iv)

    return cipher.doFinal(encryptedText)
}

fun generateRandomByteArray(size: Int): ByteArray {
    val secureRandom = SecureRandom()
    val randomBytes = ByteArray(size)
    secureRandom.nextBytes(randomBytes)

    return randomBytes
}