BCryptDuplicateHash function (bcrypt.h)

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(
  [in]            BCRYPT_HASH_HANDLE hHash,
  [out]           BCRYPT_HASH_HANDLE *phNewHash,
  [out, optional] PUCHAR             pbHashObject,
  [in]            ULONG              cbHashObject,
  [in]            ULONG              dwFlags
);

Parameters

[in] hHash

The handle of the hash or MAC object to duplicate.

[out] phNewHash

A pointer to a BCRYPT_HASH_HANDLE value that receives the handle that represents the duplicate hash or MAC object. This handle is used in subsequent hashing or MAC functions, such as the BCryptHashData function. When you have finished using this handle, release it by passing it to the BCryptDestroyHash function.

[out, optional] pbHashObject

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 from the algorithm or hash handle. This will provide the size of the hash or MAC object for the specified algorithm.

This memory can only be freed after the handle pointed to by the phHash parameter is destroyed.

If the value of this parameter is NULL and the value of the cbHashObject parameter is zero, the memory for the hash object is allocated by this function, and freed by BCryptDestroyHash. Windows 7: This memory management functionality is available beginning with Windows 7.

[in] cbHashObject

The size, in bytes, of the pbHashObject buffer.

If the value of this parameter is zero and the value of the pbHashObject parameter is NULL, the memory for the key object is allocated by this function, and freed by BCryptDestroyHash. Windows 7: This memory management functionality is available beginning with Windows 7.

[in] dwFlags

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

Return value

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

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

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.

When using a supported algorithm provider, BCryptDuplicateHash can be called either from user mode or kernel mode. Kernel mode callers can execute either at PASSIVE_LEVEL IRQL 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 BCryptDuplicateHash function must refer to nonpaged (or locked) memory.

To call this function in kernel mode, use Cng.lib, which is part of the Driver Development Kit (DDK). Windows Server 2008 and Windows Vista: To call this function in kernel mode, use Ksecdd.lib.

Requirements

See also

BCryptDuplicateHash

BCryptHashData

BCryptFinishHash

BCryptDestroyHash