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Posted 14 Mar 2002

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Encryption/Decryption with .NET

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

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.

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About the Author

Frank Fang
Web Developer
United States United States
No Biography provided

Comments and Discussions

 
QuestionHelp for PHP Pin
Member 148796552-Jul-20 19:21
MemberMember 148796552-Jul-20 19:21 
QuestionTake this down Pin
Mark Jones12-Feb-13 4:05
MemberMark Jones12-Feb-13 4:05 
GeneralMy vote of 1 Pin
Slip_915-Oct-11 0:49
MemberSlip_915-Oct-11 0:49 
GeneralMy vote of 2 Pin
ganeshJoshi27-Jul-10 23:06
MemberganeshJoshi27-Jul-10 23:06 
GeneralLet me see Pin
Abinash Bishoyi19-Jun-10 11:48
MemberAbinash Bishoyi19-Jun-10 11:48 
GeneralMy vote of 1 Pin
Tyler Xie19-Dec-08 8:55
MemberTyler Xie19-Dec-08 8:55 
GeneralPhrase I LOVE COFFEE! throws and error Pin
Dave Sopko2-Aug-07 8:23
MemberDave Sopko2-Aug-07 8:23 
GeneralRe: Phrase I LOVE COFFEE! throws and error Pin
blackjack215016-Jul-08 23:46
Memberblackjack215016-Jul-08 23:46 
GeneralRe: Phrase I LOVE COFFEE! throws and error Pin
Bruce Burge22-Apr-09 5:57
MemberBruce Burge22-Apr-09 5:57 
QuestionInvalid Length Pin
Naeem Hassan25-Jan-07 1:10
MemberNaeem Hassan25-Jan-07 1:10 
AnswerRe: Invalid Length Pin
sweemeng.koh23-Sep-07 13:19
Membersweemeng.koh23-Sep-07 13:19 
AnswerRe: Invalid Length Pin
bluebeetleRCC15-Aug-08 5:27
MemberbluebeetleRCC15-Aug-08 5:27 
AnswerRe: Invalid Length Pin
nathan2240529-May-09 4:24
Membernathan2240529-May-09 4:24 
GeneralBase64Strings Pin
lyn_s_scott26-May-05 10:33
Memberlyn_s_scott26-May-05 10:33 
GeneralRe: Base64Strings Pin
dlwiii22-Aug-08 7:26
Memberdlwiii22-Aug-08 7:26 
GeneralInvalid Length Pin
Anonymous16-Aug-04 16:58
MemberAnonymous16-Aug-04 16:58 
GeneralRe: Invalid Length Pin
vipinjosea2-Aug-05 18:17
Membervipinjosea2-Aug-05 18:17 
GeneralInvalid lenth Pin
Member 239136814-Jul-04 23:18
MemberMember 239136814-Jul-04 23:18 
GeneralRe: Invalid lenth Pin
Anonymous9-Sep-04 23:30
MemberAnonymous9-Sep-04 23:30 
GeneralRe: Invalid lenth Pin
Anonymous3-Jan-05 6:58
MemberAnonymous3-Jan-05 6:58 
GeneralRe: Invalid lenth Pin
John Storer II5-Jul-06 2:31
MemberJohn Storer II5-Jul-06 2:31 
GeneralRe: Invalid lenth Pin
shuchi agarwal28-Jul-06 3:14
Membershuchi agarwal28-Jul-06 3:14 
GeneralThe bug in encryption found... Pin
Nikolai Serdiuk25-Feb-04 23:32
MemberNikolai Serdiuk25-Feb-04 23:32 
GeneralRe: The bug in encryption found... Pin
Anonymous31-May-04 12:43
MemberAnonymous31-May-04 12:43 
GeneralRe: The bug in encryption found... Pin
Nikolai Serdiuk31-May-04 21:34
MemberNikolai Serdiuk31-May-04 21:34 

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