RE: Question about OffloadModExpo() Function

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Date: Fri, 21 Oct 2005 09:32:01 -0700

In debugger do you see at all your function called from CAPI? If not, than
maybe dll signing is the issue. Capi won't load unsigned CSPs so it's
possible that it won't load unsigned OffLoadModExpo dlls either. For testing
try to load a KERNEL debugger (because than CAPI allow to load any unsigned
dlls). If that solves your problem than it's the dll signature...

Laszlo Elteto
SafeNet, Inc.

"JohnShen" wrote:

> Hi everyone,
>
> MSDN tells that OffloadModExpo() function can offload modular exponentiation
> from a CSP to a hardware accelerator.
> But these days I've been nearly crazy about this function.
>
> I implement my own OffloadModExpo() function, which calling the ModExpo
> implementation of RSAREF library. And building to a windows DLL.
>
> Directly calling my OffloadModExpo(), encrypting & decrypting runs OK.
> But When use Crypto API, which will indirectly call OffloadModExpo(),
> encrypting & decrypting fails.
>
> My implementation is like this:
>
> ///////////////
> // .h
> _declspec (dllexport)
> BOOL /* WINAPI */ OffloadModExpo( // NOTICE: no 'WINAPI' here, if used can't
> be called by Crypto API
> BYTE *pbBase, // in
> BYTE *pbExpo, // in
> DWORD cbExpo, // in
> BYTE *pbMod, // in
> DWORD cbMod, // in
> BYTE *pbResult, // out
> void *pReserved, // reserved
> DWORD dwFlags // in
> );
>
> // .c
> BOOL /* WINAPI */ OffloadModExpo(
> BYTE *pbBase, // in
> BYTE *pbExpo, // in
> DWORD cbExpo, // in
> BYTE *pbMod, // in
> DWORD cbMod, // in
> BYTE *pbResult, // out
> void *pReserved, // reserved
> DWORD dwFlags // in
> )
> {
> // here is my implementation, calling RSAREF's NN_ModExp()
> ...
>
> return TRUE;
> }
> /////////////////
>
> I use two test programs, one is encrypting & decrypting using RSA, another
> is signing & verifying. Not calling my OffloadModExpo DLL, the two test
> programs both run OK. But when using OffloadModExpo, error occurs. One error
> come out when calling CryptDecrypt(), another is from CryptVerifySignature().
> The error code are both: ERROR_INVALID_PARAMETER.
>
>
> Then I write a program directly calling OffloadModExpo, not by Crypto API.
> This time encrypting & decrypting using RSA is OK.
> The test program is:
> //////////////////////
> #define BYTE_LEN 8
> int main(int argc, char *argv[])
> {
> // all are little endian
> BYTE enc[BYTE_LEN], decr[BYTE_LEN];
> BYTE base[BYTE_LEN] = {0x11, 0x22, 0x33, 0x44, 0x55, 0xaa, 0x1}; // BASE
> BYTE pub_expo[BYTE_LEN] = {0x01, 0, 0x01, 0}; // PUBLIC EXPO: 65537
> BYTE mod[BYTE_LEN] = {0x29, 0x5D, 0x3C, 0x33, 0x6F, 0xD2, 0x2}; //MODULAR:
> 2D26F333C5D29
> BYTE priv_expo[BYTE_LEN] = {0xE1, 0xF1, 0x85, 0xC2, 0x7A, 0x63, 0x1}; //
> PRIVATE EXPO: 1637AC285F1E1
>
>
> printf("----text %x %x %x %x %x %x %x %x\n", base[0], base[1], base[2],
> base[3], base[4], base[5], base[6], base[7]);
>
> OffloadModExpo(base, pub_expo, 3, mod, 7, enc, NULL, 0);
> printf("----encr %x %x %x %x %x %x %x %x\n", enc[0], enc[1], enc[2],
> enc[3], enc[4], enc[5], enc[6], enc[7]);
>
> OffloadModExpo(enc, priv_expo, 7, mod, 7, decr, NULL, 0);
> printf("----decr %x %x %x %x %x %x %x %x\n", decr[0], decr[1], decr[2],
> decr[3], decr[4], decr[5], decr[6], decr[7]);
>
> return 0;
> }
> ////////////////////
>
>
> So I think my ModExpo implementation is not wrong.
>
> But what's the problem in?
> I'm using VC++ 6.0, runing on Windows2k.
>
> If anyone could give me some information, I'll be very grateful.
>
> Thanks for your reading and your time.
>
> --
> John
>

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