using System;

using System.Collections.Generic;

using System.Text;

​

public class C {

    public static void Main() {

        System.Console.WriteLine(new C().HexStringToBinary("284d69f1cb048f0a0e1bbea4122ee4dd2cf2c7608527a123e5ae642f10cc8894"));

        System.Console.WriteLine(new C().HexStringToBinary("284d69f1cb"));

    }

    private static readonly Dictionary<char, string> hexCharacterToBinary = new Dictionary<char, string> {

    { '0', "0000" },

    { '1', "0001" },

    { '2', "0010" },

    { '3', "0011" },

    { '4', "0100" },

    { '5', "0101" },

    { '6', "0110" },

    { '7', "0111" },

    { '8', "1000" },

    { '9', "1001" },

    { 'a', "1010" },

    { 'b', "1011" },

    { 'c', "1100" },

    { 'd', "1101" },

    { 'e', "1110" },

    { 'f', "1111" }

};

​

public string HexStringToBinary(string hex) {

    StringBuilder result = new StringBuilder();

    foreach (char c in hex) {

        // This will crash for non-hex characters. You might want to handle that differently.

        result.Append(hexCharacterToBinary[char.ToLower(c)]);

    }

    return result.ToString();

}

}