BCryptDuplicateHash

The BCryptDuplicateHash function duplicates an existing hash or Message Authentication Code (MAC) object. The duplicate object contains all state and data contained in the original object at the point of duplication.

Syntax

NTSTATUS BCryptDuplicateHash(
         BCRYPT_HASH_HANDLE hHash,
         BCRYPT_HASH_HANDLE *phNewHash,
         PUCHAR pbHashObject,
         ULONG cbHashObject,
         ULONG dwFlags
)

Parameters

hHash
Type: BCRYPT_HASH_HANDLE

[in] The handle of the hash or MAC object to duplicate.

phNewHash
Type: BCRYPT_HASH_HANDLE *

[out] A pointer to a BCRYPT_HASH_HANDLE value that receives the handle that represents the duplicate hash or MAC object.

pbHashObject
Type: PUCHAR

[out, optional] A pointer to a buffer that receives the duplicate hash or MAC object. The cbHashObject parameter contains the size of this buffer. The required size of this buffer can be obtained by calling the BCryptGetProperty function to get the BCRYPT_OBJECT_LENGTH property. This will provide the size of the hash object for the specified algorithm.

When the duplicate hash handle is released, free this memory.

cbHashObject
Type: ULONG

[in] The size, in bytes, of the pbHashObject buffer.

dwFlags
Type: ULONG

[in] A set of flags that modify the behavior of this function. No flags are currently defined, so this parameter should be zero.

Return value

Type: NTSTATUS

Returns a status code that indicates the success or failure of the function.

Return codes

Possible return codes include, but are not limited to, the following.

Return code	Description
STATUS_SUCCESS	The function was successful.
STATUS_BUFFER_TOO_SMALL	The size of the hash object specified by the cbHashObject parameter is not large enough to hold the hash object.
STATUS_INVALID_HANDLE	The hash handle in the hHash parameter is not valid.
STATUS_INVALID_PARAMETER	One or more parameters are not valid.

Remarks

This function is useful when computing a hash or MAC over a block of common data. After the common data has been processed, the hash or MAC object can be duplicated, and then the unique data can be added to the individual objects.

Depending on what processor modes a provider supports, BCryptDuplicateHash can be called either from user mode or kernel mode. Kernel mode callers can execute either at PASSIVE_LEVELIRQL or DISPATCH_LEVEL IRQL. If the current IRQL level is DISPATCH_LEVEL, the handle provided in the hHash parameter must be derived from an algorithm handle returned by a provider that was opened by using the BCRYPT_PROV_DISPATCH flag, and any pointers passed to the BCryptDestroyKey function must refer to nonpaged (or locked) memory.

Requirements

Header: Declared in bcrypt.h.

Library: Use bcrypt.lib.