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4/8/2010

This function computes the cryptographic hash of a session key object. This function can be called multiple times with the same hash handle to compute the hash of multiple keys. Calls to the CryptHashSessionKeyfunction can be interspersed with calls to the CryptHashDatafunction.

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

Syntax 

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

Parameters

hHash

[in] HCRYPTHASHhandle to the hash object created by calling the CryptCreateHashfunction.

hKey

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

dwFlags

[in] Reserved for future use and must be set to zero.

Return Value

TRUE indicates success. FALSE indicates failure. To get extended error information, call the GetLastErrorfunction.

The following table shows the common values for the GetLastErrorfunction. The error values prefaced by NTE are generated by the particular cryptographic service provider (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 hHashhandle specifies an algorithm that this CSP does not support.

NTE_BAD_FLAGS

The dwFlagsparameter is nonzero.

NTE_BAD_HASH

The hash object specified by the hHashparameter is invalid.

NTE_BAD_HASH_STATE

An attempt was made to add data to a hash object that is already marked as 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A keyed hash algorithm is being used, but the session key is no longer valid.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 Code

Copy Code 
#include <wincrypt.h>
HCRYPTPROV hProv = 0;
HCRYPTHASH hHash = 0;
HCRYPTKEY hKey = 0;
// Get a handle to the default provider using CryptAcquireContext.
// For sample code, see <A
HREF="wce50lrfcryptacquirecontext.htm">CryptAcquireContext</A>.
...
...
// 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);
// Free the CSP handle.
if(hProv) CryptReleaseContext(hProv,0);

Requirements

Header wincrypt.h
Library coredll.lib
Windows Embedded CE Windows CE 2.10 and later
Windows Mobile Windows Mobile Version 5.0 and later

See Also