BCryptCreateHash function (bcrypt.h)

The BCryptCreateHash function is called to create a hash or Message Authentication Code (MAC) object.

Syntax

NTSTATUS BCryptCreateHash(
  [in, out]       BCRYPT_ALG_HANDLE  hAlgorithm,
  [out]           BCRYPT_HASH_HANDLE *phHash,
  [out, optional] PUCHAR             pbHashObject,
  [in]            ULONG              cbHashObject,
  [in, optional]  PUCHAR             pbSecret,
  [in]            ULONG              cbSecret,
  [in]            ULONG              dwFlags
);

Parameters

[in, out] hAlgorithm

The handle of an algorithm provider that supports the hash or MAC interface. This handle is obtained by calling the BCryptOpenAlgorithmProvider function, or may be a CNG Algorithm Pseudo-handle.

[out] phHash

A pointer to a BCRYPT_HASH_HANDLE value that receives a handle that represents the 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 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 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, optional] pbSecret

A pointer to a buffer that contains the key to use for a MAC. The cbSecret parameter contains the size of this buffer. If used with a hash algorithm, the algorithm must have been promoted to HMAC by using the BCRYPT_ALG_HANDLE_HMAC flag in BCryptOpenAlgorithmProvider.

To compute a hash, set this parameter to NULL.

[in] cbSecret

The size, in bytes, of the pbSecret buffer. If no key is used, set this parameter to zero.

[in] dwFlags

Flags that modify the behavior of the function. This can be zero or the following value:

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

When using a supported algorithm provider, BCryptCreateHash 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 hAlgorithm parameter must have been opened by using the BCRYPT_PROV_DISPATCH flag, and any pointers passed to the BCryptCreateHash function must refer to nonpaged (or locked) memory.

The caller should release phHash with BCryptDestroyHash when the object is no longer in use.

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