CPDuplicateHash

The CPDuplicateHash function is used to make an exact copy of a hash and the state the hash is in.

BOOL CPDuplicateHash(
  HCRYPTPROV hProv,    // in
  HCRYPTHASH hHash,    // in
  DWORD *pdwReserved,  // in
  DWORD dwFlags,       // in
  HCRYPTHASH phHash    // out
);

Parameters

hProv
Handle to a particular key container (or "context") within the CSP. This handle is obtained via a call to CPAcquireContext.
hHash
The handle to the hash to be duplicated.
pdwReserved
This parameter is reserved for future use and must be NULL.
dwFlags
The flag values. This parameter is reserved for future use and should always be zero.
phHash
The address of the handle to the duplicated hash.

Return Values

If the function succeeds, the return value is TRUE; Otherwise, return FALSE. When FALSE is returned, the appropriate error code (see the following table) must be set via SetLastError.

Error Description
ERROR_CALL_NOT_IMPLEMENTED Since this is a new function, existing CSPs may not implement it. This error is returned if the CSP does not support this function.
ERROR_INVALID_PARAMETER One of the parameters contains an invalid value. This is most often an illegal pointer.
NTE_BAD_HASH The handle to the original hash is not valid.

Remarks

CPDuplicateHash is used to make copies of hashes (also known as message digests) and the exact state of the hash. For example a caller may want to generate two hashes, but both hashes have to start with some common data hashed. A hash could be created, the common data hashed, a duplicate made with the CPDuplicateHash function, and then the data unique to each hash would be hashed. The handle to the duplicated hash, phHash, allows the developer to utilize the duplicated hash independently of the original hash.

CPDestroyHash must be called to destroy any hashes that are created with CPDuplicateHash. Destroying the original hash does not cause the duplicate hash to be destroyed. Once a duplicate hash is made, it is separate from the original hash. There is no shared state between the two hashes.

See Also

CPDestroyHash, CryptDuplicateHash