CipherWrapper.kt

fun decrypt(data: String, key: Key?, useInitializationVector: Boolean = false): String {
    var encodedString: String

    if (useInitializationVector) {
        val split = data.split(IV_SEPARATOR.toRegex())
        if (split.size != 2) throw IllegalArgumentException("Passed data is incorrect. There was no IV specified with it.")

        val ivString = split[0]
        encodedString = split[1]
        val ivSpec = IvParameterSpec(Base64.decode(ivString, Base64.DEFAULT))
        cipher.init(Cipher.DECRYPT_MODE, key, ivSpec)
    } else {
        encodedString = data
        cipher.init(Cipher.DECRYPT_MODE, key)
    }

    val encryptedData = Base64.decode(encodedString, Base64.DEFAULT)
    val decodedData = cipher.doFinal(encryptedData)
    return String(decodedData)
}