CryptHashSessionKey

This function is used to compute the cryptographic hash on a key object. This function can be called multiple times with the same hash handle to compute the hash on multiple keys. Calls to CryptHashSessionKey can be interspersed with calls to CryptHashData.

Before calling this function, the CryptCreateHash function must be called to get a handle to a hash object.

At a Glance

Header file:	Wincrypt.h
Windows CE versions:	2.10 and later

Syntax

BOOL WINAPI CryptHashSessionKey( HCRYPTHASH hHash, HCRYPTKEY hKey, DWORD dwFlags );

Parameters

hHash

[in] Handle to the hash object. An application obtains this handle by using the CryptCreateHash function.

hKey

[in] Handle to the key object to be hashed.

dwFlags

[in] Specifies a bitmask of flags. This parameter is reserved for future use; set to 0.

Return Values

TRUE indicates success. FALSE indicates failure. To get extended error information, call GetLastError. Common values for GetLastError are described in the following table. The error values prefaced by "NTE" are generated by the particular CSP you are using.

Value	Description
ERROR_INVALID_HANDLE	One of the parameters specifies an invalid handle.
ERROR_INVALID_PARAMETER	One of the parameters contains an invalid value. This is most often an illegal pointer.
NTE_BAD_ALGID	The hHash handle specifies an algorithm that this CSP does not support.
NTE_BAD_FLAGS	The dwFlags parameter is nonzero.
NTE_BAD_HASH	The hash object specified by the hHash parameter is invalid.
NTE_BAD_HASH_STATE	An attempt was made to add data to a hash object that is already marked "finished."
NTE_BAD_KEY	A keyed hash algorithm is being used, but the session key is no longer valid. This error will be generated if the session key is destroyed before the hashing operation is complete.
NTE_BAD_UID	The CSP context that was specified when the hash object was created cannot be found.
NTE_FAIL	The function failed in some unexpected way.

Example

#include <wincrypt.h>

HCRYPTPROV hProv = 0;
HCRYPTHASH hHash = 0;
HCRYPTKEY hKey = 0;

// Get a handle to the default provider.
if(!CryptAcquireContext(&hProv, NULL, NULL, PROV_RSA_FULL, 0)) {
 printf("Error %x during CryptAcquireContext!\n", GetLastError());
 goto done;
}

// Create a hash object.
if(!CryptCreateHash(hProv, CALG_MD5, 0, 0, &hHash)) {
 printf("Error %x during CryptBeginHash!\n", GetLastError());
 goto done;
}

// Create a random session key.
if(!CryptGenKey(hProv, CALG_RC2, CRYPT_EXPORTABLE, &hKey)) {
 printf("Error %x during CryptGenKey!\n", GetLastError());
 goto done;
}

// Compute the cryptographic hash on the key object.
if(!CryptHashSessionKey(hHash, hKey, 0)) {
 printf("Error %x during CryptHashSessionKey!\n", GetLastError());
 goto done;
}

// Use the hash of the key object. For instance, additional 
// data could be hashed and sent in a message to several recipients. 
// The recipients will be able to verify who the message originator 
// is if the key used is also exported to them..
...

done:

// Destroy the hash object.
if(hHash) CryptDestroyHash(hHash);

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

// Release the CSP handle.
if(hProv) CryptReleaseContext(hProv,0);