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Encryption/Decryption with .NET

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Introduction

Encryption and Decryption

The System.Security.Cryptographic namespace within the Microsoft .NET Framework provides a variety of tools to aid in encryption and decryption. The CryptoStream class is used here to demonstrate the encryption and decryption with System.Security.Cryptographic.SymmetricAlgorithm, such as DESCryptoServiceProvider, RC2CryptoServiceProvider, and RijndaelManaged classes.

I have searched the Internet for some samples and all I found were based on the Microsoft sample code in KB Article Q307010 which basically uses input/output files as source and destination. I would like to have the encryption and decryption done in memory without having to specify source and destination files, so that I could use the code on a web server or so.

If you have any questions, please email to: fangfrank@hotmail.com

Frank Fang

Source Code

using System;
using System.Security.Cryptography;
using System.IO;
using System.Text;

namespace FangHome_Crypto
{
    /// <summary>
    /// SymmCrypto is a wrapper of System.Security.Cryptography.SymmetricAlgorithm classes
    /// and simplifies the interface. It supports customized SymmetricAlgorithm as well.
    /// </summary>
    public class SymmCrypto
    {
        /// <remarks>
        /// Supported .Net intrinsic SymmetricAlgorithm classes.
        /// </remarks>
        public enum SymmProvEnum : int
        {
            DES, RC2, Rijndael
        }

        private SymmetricAlgorithm mobjCryptoService;

        /// <remarks>
        /// Constructor for using an intrinsic .Net SymmetricAlgorithm class.
        /// </remarks>
        public SymmCrypto(SymmProvEnum NetSelected)
        {
            switch (NetSelected)
            {
                case SymmProvEnum.DES:
                    mobjCryptoService = new DESCryptoServiceProvider();
                    break;
                case SymmProvEnum.RC2:
                    mobjCryptoService = new RC2CryptoServiceProvider();
                    break;
                case SymmProvEnum.Rijndael:
                    mobjCryptoService = new RijndaelManaged();
                    break;
            }
        }

        /// <remarks>
        /// Constructor for using a customized SymmetricAlgorithm class.
        /// </remarks>
        public SymmCrypto(SymmetricAlgorithm ServiceProvider)
        {
            mobjCryptoService = ServiceProvider;
        }

        /// <remarks>
        /// Depending on the legal key size limitations of a specific CryptoService provider
        /// and length of the private key provided, padding the secret key with space character
        /// to meet the legal size of the algorithm.
        /// </remarks>
        private byte[] GetLegalKey(string Key)
        {
            string sTemp;
            if (mobjCryptoService.LegalKeySizes.Length > 0)
            {
                int lessSize = 0, moreSize = mobjCryptoService.LegalKeySizes[0].MinSize;
                // key sizes are in bits
                while (Key.Length * 8 > moreSize)
                {
                    lessSize = moreSize;
                    moreSize += mobjCryptoService.LegalKeySizes[0].SkipSize;
                }
                sTemp = Key.PadRight(moreSize / 8, ' ');
            }
            else
                sTemp = Key;

            // convert the secret key to byte array
            return ASCIIEncoding.ASCII.GetBytes(sTemp);
        }

        public string Encrypting(string Source, string Key)
        {
            byte[] bytIn = System.Text.ASCIIEncoding.ASCII.GetBytes(Source);
            // create a MemoryStream so that the process can be done without I/O files
            System.IO.MemoryStream ms = new System.IO.MemoryStream();

            byte[] bytKey = GetLegalKey(Key);

            // set the private key
            mobjCryptoService.Key = bytKey;
            mobjCryptoService.IV = bytKey;

            // create an Encryptor from the Provider Service instance
            ICryptoTransform encrypto = mobjCryptoService.CreateEncryptor();

            // create Crypto Stream that transforms a stream using the encryption
            CryptoStream cs = new CryptoStream(ms, encrypto, CryptoStreamMode.Write);

            // write out encrypted content into MemoryStream
            cs.Write(bytIn, 0, bytIn.Length);
            cs.FlushFinalBlock();
            
            // get the output and trim the '\0' bytes
            byte[] bytOut = ms.GetBuffer();
            int i = 0;
            for (i = 0; i < bytOut.Length; i++)
                if (bytOut[i] == 0)
                    break;
                    
            // convert into Base64 so that the result can be used in xml
            return System.Convert.ToBase64String(bytOut, 0, i);
        }

        public string Decrypting(string Source, string Key)
        {
            // convert from Base64 to binary
            byte[] bytIn = System.Convert.FromBase64String(Source);
            // create a MemoryStream with the input
            System.IO.MemoryStream ms = new System.IO.MemoryStream(bytIn, 0, bytIn.Length);

            byte[] bytKey = GetLegalKey(Key);

            // set the private key
            mobjCryptoService.Key = bytKey;
            mobjCryptoService.IV = bytKey;

            // create a Decryptor from the Provider Service instance
            ICryptoTransform encrypto = mobjCryptoService.CreateDecryptor();
 
            // create Crypto Stream that transforms a stream using the decryption
            CryptoStream cs = new CryptoStream(ms, encrypto, CryptoStreamMode.Read);

            // read out the result from the Crypto Stream
            System.IO.StreamReader sr = new System.IO.StreamReader( cs );
            return sr.ReadToEnd();
        }
    }
}

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