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How to encrypt/decrypt a string

Posted on 2008-09-30
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Last Modified: 2009-08-19
I need to encrypt a string to store in a database (credit card number).  How can I do this with c#?
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Question by:centdevs
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6 Comments
 
LVL 5

Expert Comment

by:johnaryan
ID: 22605500
Try this:
SymmetricAlgorithm rijn = SymmetricAlgorithm.Create();
            MemoryStream ms = new MemoryStream(Convert.FromBase64String(sSource));
            CryptoStream cs = new CryptoStream(ms, rijn.CreateDecryptor(),
            CryptoStreamMode.Read);
 
            for (int i = 0; i < ms.Length; i++)
            {
                // the next line with throw a CryptographicException with the
                // message: "Padding is invalid and can not be removed."
                cs.ReadByte();
            }
        }

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Author Comment

by:centdevs
ID: 22605536
Do I have to store a key for this somewhere?
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Expert Comment

by:johnaryan
ID: 22605676
It uses the MachineKey as far as i know, but this can be changed.
You can do a search on CryptoStream to find out the specifics.
Here's the MSDN reference: http://msdn.microsoft.com/en-us/library/system.security.cryptography.cryptostream.aspx
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Author Comment

by:centdevs
ID: 22605872
This is pretty new to me, how do I get the encrypted string back out, cs.ToString() ?  Like if I want to create an encrypt method and a decrypt method, each that returns either an encrypted string or a decrypted string.
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Accepted Solution

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johnaryan earned 2000 total points
ID: 22606026
This is another snippet from MSDN and should do what you need.
using System;
using System.Data;
using System.Configuration;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Text;
using System.Security.Cryptography;
using System.IO;
 
namespace QueryStringEncryption
{
    public class Cryptography
    {
        #region Fields
 
        private static byte[] key = { };
        private static byte[] IV = { 38, 55, 206, 48, 28, 64, 20, 16 };
        private static string stringKey = "!5663a#KN";
 
        #endregion
 
        #region Public Methods
 
        public static string Encrypt(string text)
        {
            try
            {
                key = Encoding.UTF8.GetBytes(stringKey.Substring(0, 8));
                DESCryptoServiceProvider des = new DESCryptoServiceProvider();
                Byte[] byteArray = Encoding.UTF8.GetBytes(text);
                MemoryStream memoryStream = new MemoryStream();
                CryptoStream cryptoStream = new CryptoStream(memoryStream,
                    des.CreateEncryptor(key, IV), CryptoStreamMode.Write);
                cryptoStream.Write(byteArray, 0, byteArray.Length);
                cryptoStream.FlushFinalBlock();
                return Convert.ToBase64String(memoryStream.ToArray());
            }
            catch (Exception ex)
            {
                // Handle Exception Here
            }
            return string.Empty;
        }
 
 
 
        public static string Decrypt(string text)
        {
            try
            {
                key = Encoding.UTF8.GetBytes(stringKey.Substring(0, 8));
                DESCryptoServiceProvider des = new DESCryptoServiceProvider();
                Byte[] byteArray = Convert.FromBase64String(text);
                MemoryStream memoryStream = new MemoryStream();
                CryptoStream cryptoStream = new CryptoStream(memoryStream,
                    des.CreateDecryptor(key, IV), CryptoStreamMode.Write);
                cryptoStream.Write(byteArray, 0, byteArray.Length);
                cryptoStream.FlushFinalBlock();
                return Encoding.UTF8.GetString(memoryStream.ToArray());
            }
            catch (Exception ex)
            {
                // Handle Exception Here
            }
            return string.Empty;
        }
 
 
 
        #endregion
 
    }
 
}

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Author Comment

by:centdevs
ID: 22607346
How can I test this?  I'm trying to send the encrypt method a string, and then send the result to the decrypt method, but it catches an exception "Bad Data"
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