import javax.crypto.Cipher
import javax.crypto.SecretKey
import javax.crypto.SecretKeyFactory
import javax.crypto.spec.DESedeKeySpec

fun main() {
    // Replace the keyString with your 3DES key in hexadecimal format
    val keyString = "40021940DAAEF8EFC7BADF9BFBB501B640021940DAAEF8EF"

    try {
        // Convert hexadecimal string to byte array
        val keyBytes = hexStringToByteArray(keyString)

        // Create DESedeKeySpec from the byte array
        val keySpec = DESedeKeySpec(keyBytes)

        // Create DESede key using SecretKeyFactory
        val keyFactory = SecretKeyFactory.getInstance("DESede")
        val key: SecretKey = keyFactory.generateSecret(keySpec)

        // Calculate and print Key Check Value (KCV)
        val kcv = calculateKCV(key)
        println("Key Check Value (KCV): $kcv")
    } catch (e: Exception) {
        e.printStackTrace()
    }
}

// Function to convert hexadecimal string to byte array
fun hexStringToByteArray(hexString: String): ByteArray {
    return ByteArray(hexString.length / 2) {
        hexString.substring(it * 2, it * 2 + 2).toInt(16).toByte()
    }
}

// Function to convert byte array to hexadecimal string
fun byteArrayToHexString(bytes: ByteArray): String {
    return bytes.joinToString("") { "%02X".format(it) }
}

// Function to calculate Key Check Value (KCV) for 3DES key
fun calculateKCV(key: SecretKey): String {
    try {
        // Create a cipher with ECB mode and NoPadding
        val cipher = Cipher.getInstance("DESede/ECB/NoPadding")
        cipher.init(Cipher.ENCRYPT_MODE, key)

        // Encrypt a block of zeros and extract the first 8 hexadecimal characters
        val kcvBytes = cipher.doFinal(byteArrayOf(0, 0, 0, 0, 0, 0, 0, 0))
        val kcv = byteArrayToHexString(kcvBytes).substring(0, 16)
        println("Encrypted Zero Block: ${byteArrayToHexString(kcvBytes)}")
        return kcv
    } catch (e: Exception) {
        e.printStackTrace()
        return ""
    }
}