android-aes-gcm-initial.kt

const val TAG_LENGTH = 16

fun encrypt(key: SecretKey, message: ByteArray): Pair<ByteArray, ByteArray> {
    val cipher = Cipher.getInstance("AES/GCM/NoPadding")
    cipher.init(Cipher.ENCRYPT_MODE, key)
    val iv = cipher.iv.copyOf()
    val ciphertext = cipher.doFinal(message)
    return Pair(iv, ciphertext)
}

fun decrypt(key: SecretKey, iv: ByteArray, message: ByteArray): ByteArray {
    val cipher = Cipher.getInstance("AES/GCM/NoPadding")
    val spec = GCMParameterSpec(TAG_LENGTH * 8, iv)
    cipher.init(Cipher.DECRYPT_MODE, key, spec)
    return cipher.doFinal(message)
}