main.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Numerics;
using System.Security.Cryptography;
using System.Text;
using System.Threading.Tasks;

namespace Base58ReverseEncoder
{
    class Program
    {
        static void Main(string[] args)
        {
            var hash=new byte[160/8]; //in a normal address, this would be a ripemd160(publickey)
            var bytes=new byte[160/8+1+4]; //include space for version byte and 4 checksum bytes
            //hash is all 0 right now
            hash.CopyTo(bytes, 1); //not necessary for our case, but just for illustration
            bytes[0]=0x00; //VERSION NUMBER. Get this from base58.h or chainparams.cpp "pubkeyhash"
            using(var sha256=new SHA256Managed())
            {
               var tmp = sha256.ComputeHash(sha256.ComputeHash(bytes.Take(160/8+1).ToArray())); //include verison number, but do not include leading 4 bytes where checksum will go
               for (int i = 0; i < 4;i++)
               {
                   //take 4 bytes and add them to the end of the address bytes. this is our checksum
                   bytes[bytes.Length - 4 + i] = tmp[i];
               }
            }
            //base58 it up and it's all good
            Console.WriteLine("Address: {0}", Base58Encode(bytes));
            Console.ReadKey();
        }


        public static string Base58Encode(byte[] array)
        {
            const string ALPHABET = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz";
            string retString = string.Empty;
            BigInteger encodeSize = ALPHABET.Length;
            BigInteger arrayToInt = 0;
            for (int i = 0; i < array.Length; ++i)
            {
                arrayToInt = arrayToInt * 256 + array[i];
            }
            while (arrayToInt > 0)
            {
                int rem = (int)(arrayToInt % encodeSize);
                arrayToInt /= encodeSize;
                retString = ALPHABET[rem] + retString;
            }
            for (int i = 0; i < array.Length && array[i] == 0; ++i)
                retString = ALPHABET[0] + retString;

            return retString;
        }
    }
}