Exemple de programme C : Exportation d’une clé de session

L’exemple suivant crée une clé de session aléatoire et crée un objet BLOB de clé exportable. L’exemple illustre l’utilisation de CryptGetUserKey, CryptExportKey et les fonctions associées.

Cet exemple illustre les tâches et fonctions CryptoAPI suivantes :

• Acquisition d’un contexte fournisseur de solutions Cloud à l’aide de CryptAcquireContext.
• Accès à deux paires différentes de clés publiques/privées à l’aide de CryptGetUserKey.
• Génération d’une clé de session exportable à l’aide de CryptGenKey.
• Création d’un objet blob de clé simple contenant une clé de session à l’aide de CryptExportKey.
• Destruction d’une clé de session et accès aux deux paires de clés publiques/privées à l’aide de CryptDestroyKey.
• Libération du contexte fournisseur de solutions Cloud à l’aide de CryptReleaseContext.

Cet exemple utilise la fonction MyHandleError. Le code de cette fonction est inclus dans l’exemple. Le code pour cette fonction et d’autres fonctions auxiliaires est également répertorié sous usage général Functions.

//--------------------------------------------------------------------
// Copyright (C) Microsoft.  All rights reserved.
// This example program creates a session key and a simple key 
// BLOB holding that session key. The key BLOB can be written to disk 
// and later read from a disk file.
#pragma comment(lib, "crypt32.lib")

#include <stdio.h>
#include <windows.h>
#include <Wincrypt.h>
#define MY_ENCODING_TYPE  (PKCS_7_ASN_ENCODING | X509_ASN_ENCODING)
void MyHandleError(char *s);

void main(void)
{
//--------------------------------------------------------------------
// Declare and initialize variables.

HCRYPTPROV hProv;       // CSP handle
HCRYPTKEY hSignKey;     // Signature key pair handle
HCRYPTKEY hXchgKey;     // Exchange key pair handle
HCRYPTKEY hKey;         // Session key handle
BYTE *pbKeyBlob;        // Pointer to a simple key BLOB
DWORD dwBlobLen;        // The length of the key BLOB

//--------------------------------------------------------------------
// Acquire a cryptographic provider context handle.

if(CryptAcquireContext(
   &hProv, 
   NULL, 
   NULL, 
   PROV_RSA_FULL, 
   0)) 
{
    printf("The CSP has been acquired. \n");
}
else
{
    MyHandleError("Error during CryptAcquireContext.");
}
//--------------------------------------------------------------------
// Get a handle to the signature key.
// The signature key must exist before it can be retrieved. For more
// information, see the CryptGetUserKey documentation.

if(CryptGetUserKey(
   hProv, 
   AT_SIGNATURE, 
   &hSignKey)) 
{
    printf("The signature key has been acquired. \n");
}
else
{
    MyHandleError("Error during CryptGetUserKey for signkey.");
}
//--------------------------------------------------------------------
// Get a handle to the key exchange key.
// The key must exist before it can be retrieved. For more
// information, see the CryptGetUserKey documentation.

if(CryptGetUserKey(
   hProv, 
   AT_KEYEXCHANGE, 
   &hXchgKey)) 
{
    printf("The key exchange key has been acquired. \n");
}
else
{
    printf("Error during CryptGetUserKey exchange key.");
}
// hSignKey may be used to verify a signature. hXchgKey will be used
// to export a session key.

//--------------------------------------------------------------------
// Generate a session key.

if (CryptGenKey(     
    hProv,      
    CALG_RC4,      
    CRYPT_EXPORTABLE, 
    &hKey))
{   
    printf("Original session key is created. \n");
}
else
{
   MyHandleError("ERROR -- CryptGenKey.");
}
// Determine the size of the key BLOB and allocate memory.

if(CryptExportKey(
   hKey, 
   hXchgKey, 
   SIMPLEBLOB, 
   0, 
   NULL, 
   &dwBlobLen)) 
{
     printf("Size of the BLOB for the session key determined. \n");
}
else
{
     MyHandleError("Error computing BLOB length.");
}

if(pbKeyBlob = (BYTE*)malloc(dwBlobLen)) 
{
    printf("Memory has been allocated for the BLOB. \n");
}
else
{
    MyHandleError("Out of memory. \n");
}
//--------------------------------------------------------------------
// Export the key into a simple key BLOB.

if(CryptExportKey(
   hKey, 
   hXchgKey, 
   SIMPLEBLOB, 
   0, 
   pbKeyBlob, 
   &dwBlobLen))
{
     printf("Contents have been written to the BLOB. \n");
}
else
{
    MyHandleError("Error during CryptExportKey.");
}
//--------------------------------------------------------------------
//   At this point, other processing such as writing the key BLOB to
//   a file could be done.

//--------------------------------------------------------------------
// After all processing, clean up.

//--------------------------------------------------------------------
//  Free the memory used by the key BLOB.

free(pbKeyBlob);

// Destroy the session key.
if(hKey)
    CryptDestroyKey(hKey);

// Destroy the signature key handle.
if(hSignKey)
    CryptDestroyKey(hSignKey);

// Destroy the key exchange key handle.
if(hXchgKey)
     CryptDestroyKey(hXchgKey);

// Release the provider handle.
if(hProv) 
   CryptReleaseContext(hProv, 0);
printf("The program ran to completion without error. \n");

}// End of main                                                    

//--------------------------------------------------------------------
//  This example uses the function MyHandleError, a simple error
//  handling function, to print an error message and exit 
//  the program. 
//  For most applications, replace this function with one 
//  that does more extensive error reporting.

void MyHandleError(char *s)
{
    printf("An error occurred in running the program.\n");
    printf("%s\n",s);
    printf("Error number %x\n.",GetLastError());
    printf("Program terminating.\n");
    exit(1);
}