Hi,
I have some problems passing parameters to a function
defined in a dll written in C.
See the attached file to a description of my problem ...

Thanks !!!

The basic marshaling of WFSPINCRYPT & WFSXDATA could be:

 // ===================================================================
   Type typXD = typeof( WFSXDATA );
   int sizeXD = Marshal.SizeOf( typXD );

   WFSPINCRYPT lcsttCrypt = new WFSPINCRYPT();
   lcsttCrypt.lpsKey = new String( ' ',256 );
   lcsttCrypt.lpsStartValueKey = new String( ' ',256 );
   lcsttCrypt.lpxCryptData  = Marshal.AllocHGlobal( sizeXD );
   lcsttCrypt.lpxKeyEncKey  = Marshal.AllocHGlobal( sizeXD );
   lcsttCrypt.lpxStartValue = Marshal.AllocHGlobal( sizeXD );

   WFSXDATA lcsttCryptData = new WFSXDATA();
   lcsttCryptData.lpbData  = new String( ' ', 256 );
   lcsttCryptData.usLength =  256;
   Marshal.StructureToPtr( lcsttCryptData, lcsttCrypt.lpxCryptData, false );

   WFSXDATA lcsttKeyEncKeys =  new WFSXDATA();
   lcsttKeyEncKeys.lpbData  =  new String( ' ', 256 );
   lcsttKeyEncKeys.usLength =  0;
   Marshal.StructureToPtr( lcsttKeyEncKeys, lcsttCrypt.lpxKeyEncKey, false );

   WFSXDATA lcsttStartValue = new WFSXDATA();
   lcsttStartValue.lpbData  =  new String( ' ', 256 );
   lcsttStartValue.usLength =  0;
   Marshal.StructureToPtr( lcsttStartValue, lcsttCrypt.lpxStartValue, false );
 // ===================================================================

but I don't understand all the rest of your code
beyond your line:
 lcsttCrypt.wMode = PIN_MODEENCRYPT;
 .... ???? ....

And you didn't post the C/C++ source & documentation,
so there could still be MANY hidden translation errors.

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 Thomas Scheidegger - MVP .NET - 'NETMaster'
 http://www.cetus-links.org/oo_dotnet.html - http://dnetmaster.net/