CryptCreateHash info  Overview  Group

The CryptCreateHash function is used to initiate the hashing of a stream of data. It returns to the caller a handle to a CSP hash object. This handle can also be used in subsequent calls to CryptHashData and CryptHashSessionKey in order to hash streams of data and session keys.

BOOL CRYPTFUNC CryptCreateHash(

HCRYPTPROV hProv,
ALG_ID Algid,
HCRYPTKEY hKey,
DWORD dwFlags,
HCRYPTHASH *phHash
);

Parameters

hProv

[in] A handle to the CSP to use. An application obtains this handle using the CryptAcquireContext function.

Algid

[in] An algorithm identifier of the hash algorithm to use.

The valid values for this parameter will vary, depending on the CSP that is used. See the “Remarks” section for the list of default algorithms.

hKey

[in] If the type of hash algorithm is a keyed hash, such as a MAC algorithm, the key for the hash should be passed in this parameter. For nonkeyed algorithms, this parameter should be set to zero.

The key must be to a block cipher, such as RC2, with a cipher mode of CBC.

dwFlags

[in] The flag values. This parameter is reserved for future use and should always be zero.

phHash

[out] The address to which the function copies a handle to the new hash object.

Remarks

The Microsoft RSA Base Provider defines the following hashing algorithms:

Constant	Description
CALG_MAC	Message Authentication Code
CALG_MD2	MD2
CALG_MD5	MD5
CALG_SHA	US DSA Secure Hash Algorithm

The computation of the actual hash is done with the CryptHashData and CryptHashSessionKey functions. These require a handle to the hash object. Once all the data has been added to the hash object, exactly one of the following operations can be performed:

• The hash value can be retrieved using CryptGetHashParam.

• A session key can be derived using CryptDeriveKey.

• The hash can be signed using CryptSignHash.

• A signature can be verified using CryptVerifySignature.

Once one of the functions from this list has been called, the only hashing function that can be used with the same hash handle is CryptDestroyHash.

Return Values

If the function succeeds, the return value is nonzero.

If the function fails, the return value is zero. To retrieve extended error information, use the GetLastError function.

The following table lists the error codes most commonly returned by the GetLastError function. The error codes prefaced by “NTE” are generated by the particular CSP you are using.

Error	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.
ERROR_NOT_ENOUGH_MEMORY	The operating system ran out of memory during the operation.
NTE_BAD_ALGID	The Algid parameter specifies an algorithm that this CSP does not support.
NTE_BAD_FLAGS	The dwFlags parameter is nonzero.
NTE_BAD_KEY	A keyed hash algorithm (such as CALG_MAC) is specified by Algid and the hKey parameter is either zero or it specifies an invalid key handle. This error code will also be returned if the key is to a stream cipher, or if the cipher mode is anything other than CBC.
NTE_NO_MEMORY	The CSP ran out of memory during the operation.

Example

See the “Example” section in the CryptSignHash function.

See Also

CryptAcquireContext, CryptDeriveKey, CryptDestroyHash, CryptGetHashParam, CryptHashData, CryptHashSessionKey, CryptSignHash, CryptVerifySignature