From: satidar kumar
Can someone help me out WHY the two files encrypting the same content has different decryt content?
My Problem is to encrypt data in c++(using CryptoAPI) and decrypt it using C#
Thanks in advance.

/////////////////////////////////////////////////////////////////////////////////////////////////////
//C# code

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

namespace MySampleCryptoApp
{
    /// <summary>
    /// Summary description for Class1.
    /// </summary>
    class Class1
    {
        [STAThread]
        static void Main(string[] args)
        {
            Encrypt();
            Decrypt();
        }

        private static void Encrypt()
        {
            RC2CryptoServiceProvider RCCrypto = new RC2CryptoServiceProvider();
            RCCrypto.Mode                = CipherMode.CBC;
            RCCrypto.KeySize            = 40;
            RCCrypto.EffectiveKeySize    = 40;
            RCCrypto.BlockSize            = 64;

            UnicodeEncoding UE = new UnicodeEncoding();
            //following code ins troublesome
            //byte[] Key = UE.GetBytes("abcdefgh");

            PasswordDeriveBytes pwd = new PasswordDeriveBytes("abcdefgh",null);
            byte[] Key                = pwd.CryptDeriveKey("RC2","MD5",0,new byte[8]);


            byte[] IV = {0x00, 0x00,0x00,
                            0x00,0x00, 0x00,0x00, 0x00,0x00, 0x00,0x00, 0x00,0x00,
                            0x00,0x00, 0x00};

            FileStream oFStream = new FileStream(@"E:\Output.txt", FileMode.OpenOrCreate, FileAccess.Write);

            //Create a CryptoStream, pass it the NetworkStream, and encrypt
            //it with the RC2Crypto class.
            CryptoStream CryptStream = new
                CryptoStream(oFStream,
                RCCrypto.CreateEncryptor
                (Key, IV),
                CryptoStreamMode.Write);


            //Create a StreamWriter for easy writing to the
            //file stream.
            StreamWriter SWriter = new    StreamWriter(CryptStream);

            long lLength = oFStream.Length;
            //Write to the stream.
            //SWriter.WriteLine("abcdefgh");
            SWriter.WriteLine("ab");

            //Inform the user that the message    was written
            //to the stream.
            Console.WriteLine("The message was sent.");
            //Close all of the connections.
            SWriter.Close();
            CryptStream.Close();
            oFStream.Close();

        }
        private static void Decrypt()
        {
            UnicodeEncoding UE = new UnicodeEncoding();
            PasswordDeriveBytes pwd = new PasswordDeriveBytes("abcdefgh",null);
            byte[] Key                = pwd.CryptDeriveKey("RC2","MD5",0,new byte[8]);

            byte[] IV = {0x00, 0x00,0x00,
                            0x00,0x00, 0x00,0x00, 0x00,0x00, 0x00,0x00, 0x00,0x00,
                            0x00,0x00, 0x00};

            //FileStream oFStream = new    FileStream(@"E:\Output.txt", FileMode.Open, FileAccess.Read);
            FileStream oFStream = new    FileStream(@" E:\\Output.txt", FileMode.Open, FileAccess.Read);
            //Create a new instance of the    RC2Crypto class
            // and decrypt the stream.

            RC2CryptoServiceProvider RCCrypto  = new RC2CryptoServiceProvider();
            RCCrypto.Mode = CipherMode.CBC;
            RCCrypto.KeySize = 40;
            RCCrypto.EffectiveKeySize = 40;
            RCCrypto.BlockSize = 64;

            //Create a CryptoStream, pass it the NetworkStream, and decrypt
            //it with the Rijndael class using  key and IV.
            CryptoStream CryptStream = new CryptoStream(oFStream,
                                            RCCrypto.CreateDecryptor
                                            (Key, IV),
                                            CryptoStreamMode.Read);

            //Read the stream.
            StreamReader SReader        = new    StreamReader(CryptStream);

            //Display the message.
            Console.WriteLine("The decrypted  original message: {0}", SReader.ReadToEnd());

            //Close the streams.
            CryptStream.Close();
            SReader.Close();
            oFStream.Close();

        }
    }
}

////////////////////////////////////////////////////////////////////////////////////////////////////

// SampleCryptoNativeApp.cpp : Defines the entry point for
// the console application.
//

#include "stdafx.h"
#include "windows.h"
#include <wincrypt.h>
#include <TCHAR.h>
void PRINTERROR(char* msg){ printf(" %s : error code %d ",msg,GetLastError());}
int main(int argc, char* argv[])
{

    BOOL bResult;
    HCRYPTPROV hProv;
    HCRYPTHASH hHash;
    HCRYPTKEY hKey;
    FILE *fp ;

    BYTE *pByte = NULL;
    pByte = new BYTE[100];
    memset(pByte, 0, 100);

    DWORD dwError;

    bResult = CryptAcquireContext( &hProv,
                                    NULL, //generates default (username) keystore,
                                    MS_ENHANCED_PROV,
                                    PROV_RSA_FULL,
                                    NULL);
    if(!bResult)
       // dwError = GetLastError();
       PRINTERROR("CryptAcquireContext 1");

    bResult = CryptAcquireContext(&hProv, NULL,MS_DEF_PROV, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT);
    //bResult = CryptAcquireContext(&hProv, NULL,MS_ENHANCED_PROV, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT);
    if(!bResult)
       // dwError = GetLastError();
        PRINTERROR("CryptAcquireContext 2");

    bResult = CryptCreateHash(hProv, CALG_MD5, 0, 0,&hHash);
    if(!bResult)
       // dwError = GetLastError();
        PRINTERROR("CryptCreateHash ");

    BYTE pByteBaseData[] ={97,0,98,0,99,0,100,0,101,0,102,0,103,0,104,0};    //abcdefgh
    int nKeyLen = 16;


    bResult = CryptHashData(hHash, pByteBaseData,(DWORD) nKeyLen, 0);
    if(!bResult)
        //dwError = GetLastError();
        PRINTERROR("CryptHashData ");

    //bResult = CryptDeriveKey(hProv, CALG_RC2, hHash,CRYPT_CREATE_SALT, &hKey);
    bResult = CryptDeriveKey(hProv, CALG_RC2, hHash,CRYPT_NO_SALT, &hKey);
    if(!bResult)
        //dwError = GetLastError();
        PRINTERROR("CryptDeriveKey ");

    BYTE pByteIV[] = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};
    bResult = CryptSetKeyParam(hKey,KP_IV, pByteIV, 0);
    if(!bResult)
       // dwError = GetLastError();
        PRINTERROR("CryptSetKeyParam ");

    //char pToEncryptString[] = "abcdefgh";
    //char pToEncryptString[] = "a";

    BYTE *pToEncryptBuffer = new BYTE[100];
    memset(pToEncryptBuffer, 0, 100);
    pToEncryptBuffer[0] = 'a';
    pToEncryptBuffer[0] = 0;
    pToEncryptBuffer[0] = 'b';
    pToEncryptBuffer[0] = 0;
   // memset(pToEncryptBuffer, 0, 100);
   // memcpy(pToEncryptBuffer,pToEncryptString,_tcslen(pToEncryptString)*2);

    //DWORD dwInputLen = _tcslen(pToEncryptString)*2;
    DWORD dwInputLen    = 0x04;
    DWORD dwBufLen        = 0x20;

    bResult = CryptEncrypt(hKey, NULL, TRUE, 0,pToEncryptBuffer,&dwInputLen, dwBufLen);
    if(!bResult)
       // dwError = GetLastError();
        PRINTERROR("CryptEncrypt ");

    fp = fopen("E:\\Win32Output.txt", "w");
    for(int nIndex = 0; nIndex < (int) dwInputLen;nIndex++)
    {
        fprintf(fp, "%c", pToEncryptBuffer[nIndex]);
    }
    fclose(fp);

    /*DWORD dwOutputLen = nLen;
    bResult = CryptDecrypt(hKey, NULL, TRUE, 0, pByte,&dwOutputLen);
    if(!bResult)
        dwError = GetLastError();

    bResult = CryptDecrypt(hKey, NULL, TRUE, 0,pToEncryptBuffer, &dwOutputLen);
    if(!bResult)
        dwError = GetLastError();*/

    return 0;
}

-----------------------
Posted by a user from .NET 247 (http://www.dotnet247.com/)

<Id>OCArCUTvl0+ps7rTWX+pGA==</Id>

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