Notification based flows

import java.math.BigInteger;
import java.nio.charset.StandardCharsets;
import java.security.MessageDigest;
import java.util.Base64;

public class NotificationVerificationCode {

    public static void main(String[] args) throws Exception {

        String rpChallengeBase64 = "GYS+yoah6emAcVDNIajwSs6UB/M95XrDxMzXBUkwQJ9YFDipXXzGpPc7raWcuc2+TEoRc7WvIZ/7dU/iRXenYg==";
        byte[] rpChallengeBytes = Base64.getDecoder().decode(
            rpChallengeBase64
        );

        MessageDigest md = MessageDigest.getInstance("SHA-256");
        md.update(rpChallengeBytes);
        byte[] sha256Hash = md.digest();

        BigInteger LAST_2_BYTES_BITMASK = new BigInteger("65535");

        BigInteger result = new BigInteger(sha256Hash)
            .and(LAST_2_BYTES_BITMASK)
            .mod(new BigInteger("10000"));

        String verificationCode = String.format("%04d", result);

        System.out.println(verificationCode);
    }
}

<?php

$rpChallengeBase64 = base64_decode('GYS+yoah6emAcVDNIajwSs6UB/M95XrDxMzXBUkwQJ9YFDipXXzGpPc7raWcuc2+TEoRc7WvIZ/7dU/iRXenYg==');
$sha256Hash = hash('sha256', $rpChallengeBase64, true);
$result = hexdec(bin2hex(substr($sha256Hash, -2))) % 10000;
$verificationCode = sprintf('%04d', $result);
echo $verificationCode;

?>

import base64
import hashlib

rp_challenge_base64 = b"GYS+yoah6emAcVDNIajwSs6UB/M95XrDxMzXBUkwQJ9YFDipXXzGpPc7raWcuc2+TEoRc7WvIZ/7dU/iRXenYg=="
rp_challenge_bytes = base64.b64decode(rp_challenge_base64)
sha256_hash = hashlib.sha256(rp_challenge_bytes).digest()

result = int.from_bytes(sha256_hash[-2:], byteorder='big') % 10000
verification_code = f"{result:04d}"
print(verification_code)

package main

import (
	"crypto/sha256"
	"encoding/base64"
	"fmt"
)

func main() {
	var rpChallengeBase64 string = "GYS+yoah6emAcVDNIajwSs6UB/M95XrDxMzXBUkwQJ9YFDipXXzGpPc7raWcuc2+TEoRc7WvIZ/7dU/iRXenYg=="
	var rpChallengeBytes, err = base64.StdEncoding.DecodeString(rpChallengeBase64)
	if err != nil {
		panic(err)
	}

	var sha256Hash [32]byte = sha256.Sum256(rpChallengeBytes)
	var result int = int(sha256Hash[len(sha256Hash)-2])<<8 + int(sha256Hash[len(sha256Hash)-1])
	result %= 10000

	var verificationCode string = fmt.Sprintf("%04d", result)
	fmt.Printf("%s\n",verificationCode)
}

use base64::decode;
use sha2::{Sha256, Digest};

fn main() {
    let rp_challenge_base64: &str = "GYS+yoah6emAcVDNIajwSs6UB/M95XrDxMzXBUkwQJ9YFDipXXzGpPc7raWcuc2+TEoRc7WvIZ/7dU/iRXenYg==";
    let rp_challenge_bytes = decode(rp_challenge_base64).unwrap();
    let sha256_hash = Sha256::digest(&rp_challenge_bytes);
    let result = (((sha256_hash[30] as u16) << 8) + (sha256_hash[31] as u16)) % 10000;
    let verification_code: String = format!("{:04}", result);
    println!("{}", verification_code);
}

import java.math.BigInteger
import java.nio.charset.StandardCharsets
import java.security.MessageDigest
import java.util.Base64

fun main() {
    val rpChallengeBase64: String = "GYS+yoah6emAcVDNIajwSs6UB/M95XrDxMzXBUkwQJ9YFDipXXzGpPc7raWcuc2+TEoRc7WvIZ/7dU/iRXenYg=="
    val rpChallengeBytes: ByteArray = Base64.getDecoder().decode(rpChallengeBase64)

    val sha256Hash: ByteArray = MessageDigest
        .getInstance("SHA-256")
        .digest(rpChallengeBytes)

    val LAST_2_BYTES_BITMASK: BigInteger = BigInteger("65535")

    val result: BigInteger = BigInteger(sha256Hash)
        .and(LAST_2_BYTES_BITMASK)
        .mod(BigInteger("10000"))

    val verificationCode = "%04d".format(result)

    println(verificationCode)
}

using System;
using System.Security.Cryptography;

public class NotificationVerificationCode
{
    public static void Main(string[] args)
    {
        string rpChallengeBase64 = "GYS+yoah6emAcVDNIajwSs6UB/M95XrDxMzXBUkwQJ9YFDipXXzGpPc7raWcuc2+TEoRc7WvIZ/7dU/iRXenYg==";
        byte[] rpChallengeBytes = Convert.FromBase64String(rpChallengeBase64);

        using (SHA256 sha256 = SHA256.Create())
        {
            byte[] sha256Hash = sha256.ComputeHash(rpChallengeBytes);
            int result = ((sha256Hash[30] << 8) + (sha256Hash[31])) % 10000;
            string verificationCode = result.ToString("D4");
            Console.WriteLine(verificationCode);
        }
    }
}

const crypto = require('crypto');

const rpChallenge = Buffer.from('GYS+yoah6emAcVDNIajwSs6UB/M95XrDxMzXBUkwQJ9YFDipXXzGpPc7raWcuc2+TEoRc7WvIZ/7dU/iRXenYg==', 'base64');

const sha256 = crypto.createHash('sha256');
sha256.update(rpChallenge);
const sha256Hash = sha256.digest();

const result = sha256Hash.readUInt16BE(30) % 10000
  .toString()
  .padStart(4, '0');

console.log(result);

require 'base64'
require 'digest'

rp_challenge = "GYS+yoah6emAcVDNIajwSs6UB/M95XrDxMzXBUkwQJ9YFDipXXzGpPc7raWcuc2+TEoRc7WvIZ/7dU/iRXenYg=="
sha256_hash = Digest::SHA256.digest(Base64.decode64(rp_challenge))

last_2_bytes = sha256_hash[-2..-1].unpack('n*').first

result = (last_2_bytes % 10_000).to_s.rjust(4, '0')

puts result