How to obtain a session key for plain text with the cryptographic API

Operating environment: VC6 SP5, Sp1,nt4 SP3.

It is important to get a session key in the usual programming. However, Microsoft's cryptographic Operations API (either Basic or enhanced) does not provide this functionality. CryptExportKey () and Cryptimportkey () each require a valid key handle to encrypt and decrypt the session key. MSDN shows a way to use a private key. But Microsoft's example in MSDN is quite a long one. The following method is not only faster and more efficient.

Before running this example, you need to set the following parameters in Project-> settings (Visual Studio 6.0):

1. Add C + + preprocessing definition: _win32_winnt=0x0500, _crypt32_ (Win2K) or _win32_winnt=0x0400, _crypt32_ (NT4)

2. Join the Library connection: Crypt32.lib

The example code is as follows:

#include


#include


#include


#define Key_pair_size dwSize-12


#define Session_key_size dwkeymaterial


void Main ()


{


　


Hcryptprov Hprov = 0;


Hcryptkey hexchangekeypair = 0;


Hcryptkey hsessionkey = 0;


BYTE *pbkeymaterial = NULL;


DWORD dwkeymaterial;


BYTE *pbexportedkeyblob = NULL;


BYTE *pbencryptedkey = NULL;


DWORD dwsize;


unsigned int c;


　　　


__try


　 {


　　　


if (! CryptAcquireContext (&hprov,


"Container Name",


Ms_enhanced_prov,


Prov_rsa_full,


crypt_machine_keyset))


　　{


__leave;


　　}


　


　　//---------------------------------------------------


//Create a session key. In this example we will use a 168-bit 3DES key.


if (! CryptGenKey (Hprov, Calg_3des,


crypt_exportable, &hsessionkey))


　　{


__leave;


　　}


　　//---------------------------------------------------


//Get the handle of the exchange key pair


　　　　　　　　


if (! Cryptgetuserkey (Hprov, At_keyexchange, &hexchangekeypair))


　　{


__leave;


　　}


　　//--------------------------------------------------------


//The session key is encrypted with the public key part of the key pair


//First gets the necessary byte size for the encrypted session key


//And then output it.


　　　　


if (! CryptExportKey (hSessionKey,


Hexchangekeypair,


Simpleblob,


0,


NULL,


&dwsize))


　　{


__leave;


　　}


Pbexportedkeyblob = new Byte[dwsize];


if (! CryptExportKey (hSessionKey,


Hexchangekeypair,


Simpleblob,


0,


Pbexportedkeyblob,


&dwsize))


　　{


__leave;


　　}


　


　　//--------------------------------------------------------


//We delete the first 12 byte size blob information


　　　　


Pbencryptedkey = new BYTE [key_pair_size];


　　　　


for (c = 0; c < key_pair_size C + +)


　　{


Pbencryptedkey[c] = pbexportedkeyblob[c+12];


　　}


　　　　


　　//--------------------------------------------------------


//This is when we use the private key part of the key pair to get the value of the session key.


　　　　


if (! CryptDecrypt (Hexchangekeypair, 0,


TRUE, 0,


Pbencryptedkey, &dwkeymaterial))


　　{


__leave;


　　}


　　　　


　　//-------------------------------------------------------

The value of the key is stored in the
//pbkeymaterial


　　　　


pbkeymaterial = new byte[session_key_size];


　　　　


for (c = 0; c < session_key_size C + +)


　　{


Pbkeymaterial[c] = pbencryptedkey[c];


　　}


　


　 }


__finally


　 {


if (pbkeymaterial) LocalFree (pbkeymaterial);


if (hsessionkey) Cryptdestroykey (hSessionKey);


if (hexchangekeypair) Cryptdestroykey (Hexchangekeypair);


if (Hprov)


　　　{　


CryptReleaseContext (Hprov, 0);


　　　}


　


　 }


}//End