using System;

using System.Security.Cryptography;

using System.Text;

public class Program

{

    public static void Main()

    {

        var password = "asdf123";

        var legacyPasswordSalt = "MTIzNDU=";

        var legacyPasswordHash = GenerateLegacyPasswordHash(password, legacyPasswordSalt);

        var legacyPasswordHashNET6 = GenerateLegacyPasswordHashNET6(password, legacyPasswordSalt);

        Console.WriteLine("Old : " + legacyPasswordHash);

        Console.WriteLine("NET6: " + legacyPasswordHashNET6);

        Console.WriteLine("\nAre equal: " + string.Equals(legacyPasswordHash, legacyPasswordHashNET6));

    }

    public static string GenerateLegacyPasswordHash(string password, string legacyPasswordSalt)

    {

        var passwordBytes = Encoding.Unicode.GetBytes(password);

        var legacyPasswordSaltBytes = Convert.FromBase64String(legacyPasswordSalt);

​

        var buffer = new byte[legacyPasswordSaltBytes.Length + passwordBytes.Length];

        legacyPasswordSaltBytes.CopyTo(buffer, 0);

        passwordBytes.CopyTo(buffer, legacyPasswordSaltBytes.Length);

​

        var sha = new SHA1CryptoServiceProvider();

        var result = sha.ComputeHash(buffer);

​

        var legacyPasswordHash = Convert.ToBase64String(result);

        return legacyPasswordHash;

    }

    public static string GenerateLegacyPasswordHashNET6(string password, string legacyPasswordSalt)

    {

        var passwordBytes = Encoding.Unicode.GetBytes(password);

        var legacyPasswordSaltBytes = Convert.FromBase64String(legacyPasswordSalt);

​

        var buffer = new byte[legacyPasswordSaltBytes.Length + passwordBytes.Length];

        legacyPasswordSaltBytes.CopyTo(buffer, 0);

        passwordBytes.CopyTo(buffer, legacyPasswordSaltBytes.Length);

​

        var sha = SHA1.Create();

        var result = sha.ComputeHash(buffer);

​

        var legacyPasswordHash = Convert.ToBase64String(result);

        return legacyPasswordHash;

    }

}