using System;

using System.IO;

using System.Security;

using System.Text;

using Microsoft.VisualBasic;

using System.Security.Cryptography;

using System.Text.RegularExpressions;

using System.Web.Configuration;

​

public class Program

{

    private static byte[] m_Key = new byte[8];

    private static byte[] m_IV = new byte[8];

    public static void Main()

    {

        var plainPassword = DecryptData("key4intotheblue", "snW9MAvMKSVMe+JOklH7GQ==");

        Console.WriteLine(string.Format("Password is: {0}", plainPassword));

    }

​

    public static string DecryptData(string strKey, string strData)

    {

        string strResult;

        // //1. Generate the Key used for decrypting

        if (!InitKey(strKey))

        {

            strResult = "Error. Failed to generate key for decryption";

            return strResult;

        }

​

        // //2. Initialize the service provider

        int nReturn = 0;

        DESCryptoServiceProvider descsp = new DESCryptoServiceProvider();

        ICryptoTransform desDecrypt = descsp.CreateDecryptor(m_Key, m_IV);

        // //3. Prepare the streams:

        // //   mOut is the output stream. 

        // //   cs is the transformation stream.

        MemoryStream mOut = new MemoryStream();

        CryptoStream cs = new CryptoStream(mOut, desDecrypt, CryptoStreamMode.Write);

        // //4. Remember to revert the base64 encoding into a byte array to restore the original encrypted data stream

        byte[] bPlain = new byte[strData.Length + 1];

        try

        {

            bPlain = Convert.FromBase64CharArray(strData.ToCharArray(), 0, strData.Length);

        }

        catch (Exception ex)

        {

            strResult = "Error. Input Data is not base64 encoded.";

            return strResult;

        }

​

        long lRead = 0;

        long lTotal = strData.Length;

        try

        {

            // //5. Perform the actual decryption

            while ((lTotal >= lRead))

            {

                cs.Write(bPlain, 0, System.Convert.ToInt32(bPlain.Length));

                // //descsp.BlockSize=64

                lRead = mOut.Length + System.Convert.ToInt64(Convert.ToInt32(((bPlain.Length / (double)descsp.BlockSize) * descsp.BlockSize)));

            }

​

            ASCIIEncoding aEnc = new ASCIIEncoding();

            strResult = aEnc.GetString(mOut.GetBuffer(), 0, System.Convert.ToInt32(mOut.Length));

            // //6. Trim the string to return only the meaningful data

            // //   Remember that in the encrypt function, the first 5 character holds the length of the actual data

            // //   This is the simplest way to remember to original length of the data, without resorting to complicated computations.

            string strLen = strResult.Substring(0, 5);

            int nLen = Convert.ToInt32(strLen);

            strResult = strResult.Substring(5, nLen);

            nReturn = System.Convert.ToInt32(mOut.Length);

            return strResult;

        }

        catch (Exception ex)

        {

            strResult = "Error. Decryption Failed. Possibly due to incorrect Key or corrputed data";

            return strResult;

        }

    }

​

    private static bool InitKey(string strKey)

    {

        try

        {

            // // Convert Key to byte array

            byte[] bp = new byte[strKey.Length + 1];

            ASCIIEncoding aEnc = new ASCIIEncoding();

            aEnc.GetBytes(strKey, 0, strKey.Length, bp, 0);

            // //Hash the key using SHA1

            SHA1CryptoServiceProvider sha = new SHA1CryptoServiceProvider();

            byte[] bpHash = sha.ComputeHash(bp);

            int i;

            // // use the low 64-bits for the key value

            for (i = 0; i <= 7; i++)

                m_Key[i] = bpHash[i];

            for (i = 8; i <= 15; i++)

                m_IV[i - 8] = bpHash[i];

            return true;

        }

        catch (Exception ex)

        {

            // //Error Performing Operations

            return false;

        }

    }

}