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Encryption/Decryption with .NET

, 14 Mar 2002
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A .NET SymmetricAlgorithm security class wrapper for in memory encryption/decryption with a private key
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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();
        }
    }
}

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

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About the Author

Frank Fang
Web Developer
United States United States
No Biography provided

Comments and Discussions

 
GeneralMy vote of 1 PinmemberSlip_915-Oct-11 0:49 

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