Re: Problem with cryptoapi

"Ashwani" <>
Fri, 17 Nov 2006 20:27:00 +0530
Thanks for replying. I am using MS_DEF_PROV while calling
CryptAcquireContext(). The code for generating the key and writing it in a
file is as follows-

//Code for writing key in a file
BOOL CEncryption::WritePrivateKey(FILE* pDestination, HCRYPTKEY
hPrivateKey )
 BOOL bSuccess = FALSE;
 DWORD dwBlobLen = 0;
 LPBYTE lpPrivateKey= NULL;

     // Get a private key
 hPrivateKey = GeneratePrivateKey( &lpPrivateKey, &dwBlobLen,

  // If we succeeded in getting a private key...
 if( lpPrivateKey )
   // Write the size of the private key to the destination file
  if( fwrite( &dwBlobLen, sizeof(dwBlobLen), 1, pDestination ) )
    // Write the private key (encrypted) to the destination file
   if( fwrite( lpPrivateKey, sizeof(BYTE), dwBlobLen, pDestination ) ==
dwBlobLen )
    bSuccess = TRUE;

 return bSuccess;

//code for generating the key and exporting the key.
HCRYPTKEY CEncryption::GeneratePrivateKey( LPBYTE* lpPrivateKeyBlob,
                                                 LPDWORD lpdwBlobSize,
                                        int enumAlgorithm)
 CMyApp *pApp=(CMyApp*)AfxGetApp();
 //HCRYPTKEY hPrivateKey = NULL;
 BOOL /*bInit,*/ bCryptGen;

 //Generate the private key
 BOOL bSuccess;

   bSuccess=CryptAcquireContextA( (unsigned long *)&m_hContext,
        "My Container", MS_DEF_PROV_A, PROV_RSA_FULL, 0 );

  bSuccess = CryptAcquireContext( (unsigned long *)&m_hContext,
         _T("My Container"),
  int a = GetLastError();
 int a = GetLastError();
 bCryptGen = CryptGenKey( m_hContext, enumAlgorithm, CRYPT_EXPORTABLE,
&hPrivateKey );

 if(bSuccess && bCryptGen)
   // Get handle to the encrypter's exchange public key
  if( CryptGetUserKey(m_hContext, AT_KEYEXCHANGE, &hPublicKey ) )
    // Determine size of the key blob
   if( CryptExportKey( hPrivateKey,
        0, NULL,
        lpdwBlobSize ))
    (*lpPrivateKeyBlob) = (LPBYTE)malloc( sizeof(BYTE) * (*lpdwBlobSize) );
    ATLASSERT( lpPrivateKeyBlob != NULL );

    if( lpPrivateKeyBlob )
      // Encrypt and export private key
     CryptExportKey( hPrivateKey,
         lpdwBlobSize );

 if( hPublicKey )
  CryptDestroyKey( hPublicKey );

 return hPrivateKey;

"Ashwani" <> wrote in message

Hi, i am using cryptoapi to encrypt my files. The files are decrypted if i
decrypt them on the same system with same user, but if i try to decrypt


with different user or on different system, decryption fails. The function


am using to encrypt files are:-
        CryptGetUserKey( );
        CryptGetUserKey( );
The fuction failing on decryption is
Can anybody tell how to decrypt files on a different system;

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