Hi Mike,

Thanks for your reply.

This is what I'm trying to do:

There is an existing c++ application which creates a MAC signature /
hash for a message using the MS CryptoAPI. It calls the
CryptHashMessage method on the API with a hardcoded 256 byte key and
uses szOID_RSA_MD5 as the algorithm. szOID_RSA_MD5 is a constant which
maps to "1.2.840.113549.1.1.4".

The following is a code snippet from the c++ app:

   CRYPT_HASH_MESSAGE_PARA stHashParms;  
    BYTE * paHashBuffer = NULL;
    DWORD dwHashBufferSize = DEFAULT_HASH_BUFFER_SIZE;
    const BYTE* rgpbToBeHashed[3];    
    DWORD rgcbToBeHashed[3];

    DebugTrace(_T("CSecureDataMgr::HashData() has been called. Data
buffer size is (%d) bytes. Context buffer size is (%d)
bytes."),bufBytesData1.m_dwSize,bufBytesData2.m_dwSize);

    // Initialize hashing parameters.
    ZeroMemory(&stHashParms,sizeof(stHashParms));
    ZeroMemory(&rgpbToBeHashed,sizeof(rgpbToBeHashed));
    ZeroMemory(&rgcbToBeHashed,sizeof(rgcbToBeHashed));

    // We want hash the contents of the BSTR
    stHashParms.cbSize = sizeof(stHashParms);
   
    // Set the encoding type.
    stHashParms.dwMsgEncodingType = X509_ASN_ENCODING |
PKCS_7_ASN_ENCODING;

    // Set the cryptographic provider name to null (this will default to
RSA)
    stHashParms.hCryptProv = NULL;

    // set auxillary info to null (we dont use it)
    stHashParms.pvHashAuxInfo = NULL;

    // Set the algorithm used to perform the hashing. Note we opt for RSA
MD5 here.
    stHashParms.HashAlgorithm.pszObjId = szOID_RSA_MD5; //algorithm
    stHashParms.HashAlgorithm.Parameters.cbData = 0;

    while (SUCCEEDED(hr) && (bufHashBuffer.m_pBytes == NULL))
    {
        // initialize hashing buffer structure
        rgpbToBeHashed[0] = g_abCSecureDataMgrKey;  //this is the key
        rgcbToBeHashed[0] = sizeof(g_abCSecureDataMgrKey);
        rgpbToBeHashed[1] = bufBytesData1.m_pBytes;
        rgcbToBeHashed[1] = bufBytesData1.m_dwSize;
        rgpbToBeHashed[2] = bufBytesData2.m_pBytes;
        rgcbToBeHashed[2] = bufBytesData2.m_dwSize;

        //  Allocate and intialize a buffer to receive the hashed value.
        bufHashBuffer.Alloc(dwHashBufferSize);

        // Attempt to hash the message.
        bHashed = CryptHashMessage(&stHashParms,
                                  TRUE,
                                  3,
                                  rgpbToBeHashed,
                                  rgcbToBeHashed,
                                  NULL,
                                  NULL,
                                  bufHashBuffer.m_pBytes,
                                  &dwHashBufferSize);

****************************************************************************

My task is to replicate this exact functionality in Java. (i.e. to be
able to create a MAC for a message in Java, which can then be
re-created by the C++).

I have tried using a Mac object, instantiating it with the same key
and calling the "HmacMD5" algorithm. The hash I receive in Java is
different to the c++ value... I tried doing some tricks like reversing
the byte order and adding a null byte to the end of the message.
Apparently these are well known CryptoAPI -> JCE compatability issues.

My next avenue is to try using the Signature object with the
"MD5withRSA" algorithm (this is one of the algorithms that the IBM JCE
Signature object supports).
In order to create a Signature object in Java, I need a PrivateKey.
However, all I have available to me is the hardcoded 256 byte array
that the C++ app is using.

To be honest I'm not even sure if I'm on the right track here.
"MD5withRSA" sounds very similar to the szOID_RSA_MD5 which the C++ is
using, so I thought its worth a try.

Any suggestions would be greatly appreciated!

Thanks,

Adrian