MinecraftSha.cs

using System;
using System.Text;
using System.Security.Cryptography;
using System.Numerics;

public class Test
{
    public static void Main()
    {
        Console.WriteLine("Notch: " + MinecraftShaDigest("Notch"));
        Console.WriteLine("jeb_: " + MinecraftShaDigest("jeb_"));
        Console.WriteLine("simon: " + MinecraftShaDigest("simon"));
    }
    
    public static String MinecraftShaDigest(String input) 
    {
        var hash = new SHA1Managed().ComputeHash(Encoding.UTF8.GetBytes(input));
        // Reverse the bytes since BigInteger uses little endian
        Array.Reverse(hash);
        
        BigInteger b = new BigInteger(hash);
        // very annoyingly, BigInteger in C# tries to be smart and puts in
        // a leading 0 when formatting as a hex number to allow roundtripping 
        // of negative numbers, thus we have to trim it off.
        if (b < 0)
        {
            // toss in a negative sign if the interpreted number is negative
            return "-" + (-b).ToString("x").TrimStart('0');
        }
        else
        {
            return b.ToString("x").TrimStart('0');
        }
    }
}