C++ & C# 调用 CryptEncrypt 和 CryptDecrypt

Question

Hello i am trying to Encrypt and Decrypt between C++ and C# have made a dll project using CryptEncrypt wincrypt here code i used C++

#include <Windows.h>
#include <stdio.h>
extern "C" __declspec(dllexport)

BOOL EncryptData(char* szData, char* szPassword, char* szErroror, BYTE* pData, BYTE* pDataLen, BOOL Encrypt)
{
    HANDLE hSourceFile = INVALID_HANDLE_VALUE;
    HANDLE hDestinationFile = INVALID_HANDLE_VALUE;

    HCRYPTPROV hProv = NULL;
    HCRYPTKEY hKey = NULL;
    HCRYPTKEY hXchgKey = NULL;
    HCRYPTHASH hHash = NULL;

    PBYTE pbKeyBlob = NULL;
    DWORD dwKeyBlobLen;

    PBYTE pbBuffer = NULL;
    DWORD dwBlockLen = 0;
    DWORD dwBufferLen = 0;
    DWORD dwCount = 0;
    bool bRet = true;

    int len = strlen(szData);

    if (!CryptAcquireContext(&hProv, NULL, MS_ENHANCED_PROV, PROV_RSA_FULL, 0))
    {
        if (!CryptAcquireContext(&hProv, NULL, MS_ENHANCED_PROV, PROV_RSA_FULL, CRYPT_NEWKEYSET))
            return false;
    }

    // Create a hash object.
    if (!CryptCreateHash(hProv, CALG_MD5, 0, 0, &hHash))
        return false;

    // Hash in the password data.
    if (!CryptHashData(hHash, (BYTE*)szPassword, strlen(szPassword), 0))
        return false;

    // Derive a session key from the hash object.
    if (!CryptDeriveKey(hProv, CALG_RC4, hHash, 0x00800000, &hKey))
        return false;

    dwBlockLen = 1000 - 1000 % 8;

    // Allocate memory.
    if ((pbBuffer = (BYTE*)malloc(dwBufferLen)) == NULL)
        return false;

    if (Encrypt)
    {
        if (!CryptEncrypt(hKey, 0, false, 0, pbBuffer, &dwCount, dwBufferLen))
        {
            DWORD  dwError = GetLastError();
            strcpy(szErroror, "CryptEncrypt Failed Error ");
            char szError[10];
            memset(szError, 0, 10);
            sprintf(szError, "%d", dwError);
            strcat(szErroror, szError);
            bRet = false;
        }
    }
    else
    {
        if (!CryptDecrypt(hKey, 0, false, 0, pbBuffer, &dwCount))
        {
            DWORD  dwError = GetLastError();
            strcpy(szErroror, "CryptDecrypt Failed Error ");
            char szError[10];
            memset(szError, 0, 10);
            sprintf(szError, "%d", dwError);
            strcat(szErroror, szError);
            bRet = false;
        }
    }

    char szDataLen[16];
    memset(szDataLen, 0, 16);
    sprintf(szDataLen, "%d", dwCount);
    memcpy(pDataLen, szDataLen, 16);

    BYTE* pMyData = (BYTE*)malloc(len);

    memset(pMyData, 0, len);
    memcpy(pData, pbBuffer, len);

    // Free memory.
    if (pbKeyBlob) free(pbKeyBlob);
    if (pbBuffer) free(pbBuffer);
    if (pMyData) free(pMyData);

    // Destroy session key.
    if (hKey) CryptDestroyKey(hKey);

    // Release key exchange key handle.
    if (hXchgKey) CryptDestroyKey(hXchgKey);

    // Destroy hash object.
    if (hHash) CryptDestroyHash(hHash);

    // Release provider handle.
    if (hProv) CryptReleaseContext(hProv, 0);

    return bRet;
}

And C# Project Calling the dll and the funcation

namespace ConsoleApp1
{
    class Program
    {
        [DllImport("Project3.dll", CallingConvention = CallingConvention.Cdecl)]
        [return: MarshalAs(UnmanagedType.Bool)]
        public static extern bool EncryptData(byte[] szData, char[] szPassword, StringBuilder sbError, byte[] pData, byte[] pDataLen, bool Encrypt);

        static void Main(string[] args)
        {

            StringBuilder sbError = new StringBuilder(255);
            byte[] szData = Encoding.ASCII.GetBytes("datatest");
            char[] szPassword = ("test").ToCharArray();
            byte[] pData = new byte[1008];
            byte[] pDataLen = new byte[16];
            Console.WriteLine("Encrypt");
            bool bRet = EncryptData(szData, szPassword, sbError, pData, pDataLen, true);

            Console.WriteLine(Encoding.ASCII.GetString(pData));

            Console.WriteLine("Decrypt");
            bool bRet2 = EncryptData(szData, szPassword, sbError, pData, pDataLen, false);
            Console.WriteLine(Encoding.ASCII.GetString(pData));

            Console.ReadKey();

        }
    }
}

but i have a problem with Decrypt

out

Encrypt ??rc?
Decrypt datatestx?

Encrypt 1?8V?6N5l???
Decrypt d ?? -

as you can see the Decrypt is wrong what could be wrong

Answer 1

First of all your C/C++ code uses deprecated Windows functions, secondly, there are a lot of "unsecure" C runtime functions used like: "strcpy", "strcat", "sprintf" etc. etc., thirdly not all code is guarding against buffer coding errors. The C code as is does not compile in any recent Visual Studio compiler without significant corrections.

Pls try fixing all errors, simplify code and post it again.

On the C# side, data buffers that are passed to C code are not pinned and can be moved by GC at any time. Due to its small size, they could be eagerly promoted from Gen 0 to Gen 1 by GC what will cause memory move operation and invalidation of the pointer to buffer. To put it simply pointers to all buffers may be invalid at the moment they are read by C code.

On the C# side you could do the following:

    [DllImport("Project3.dll", CallingConvention = CallingConvention.Cdecl)]
    [return: MarshalAs(UnmanagedType.Bool)]
    public static unsafe extern bool EncryptData(
        byte* szData, char* szPassword, StringBuilder sbError, byte* pData, byte* pDataLen, bool Encrypt);

    static unsafe void Main(string[] args)
    {
        StringBuilder sbError = new StringBuilder(255);
        byte[] szDataBuff = Encoding.ASCII.GetBytes("datatest");
        char[] szPasswordBuff = ("test").ToCharArray();
        byte[] pDataBuff = new byte[1008];
        byte[] pDataLenBuff = new byte[16];

        fixed (byte* szData = szDataBuff)
        fixed (char* szPassword = szPasswordBuff)
        fixed (byte* pData = pDataBuff)
        fixed (byte* pDataLen = pDataLenBuff)
        {
            Console.WriteLine("Encrypt");
            bool bRet = EncryptData(szData, szPassword, sbError, pData, pDataLen, true);

            Console.WriteLine("Encrypted: {0}", bRet);
            Console.WriteLine(Marshal.PtrToStringAnsi((IntPtr)pData));

            Console.WriteLine("Decrypt");
            bool bRet2 = EncryptData(szData, szPassword, sbError, pData, pDataLen, false);
            Console.WriteLine("Derypted: {0}", bRet2);
            Console.WriteLine(Marshal.PtrToStringAnsi((IntPtr)pData));
        }

        Console.ReadKey();
    }

There are other approaches possible but this one seems to be most straightforward and simple.