CryptSetHashParam info  Overview  Group

The CryptSetHashParam function, in theory, allows applications to customize the operations of a hash object. Currently, only a single parameter is defined for this function.

BOOL CRYPTFUNC CryptSetHashParam(

Parameters

hHash

[in] A handle to the hash object on which to set parameters.

dwParam

[in] The parameter number. See the “Remarks” section for a list of valid parameters.

pbData

[in] The parameter data buffer. Place the parameter data in this buffer before calling CryptSetHashParam. The form of this data will vary, depending on the parameter number.

dwFlags

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

Remarks

The dwParam parameter can be set to one of the following values:

HP_HASHVAL

Hash value. The pbData buffer should contain a byte array containing a hash value to place directly into the hash object. Before setting this parameter, the size of the hash value should be determined by reading the HP_HASHSIZE parameter with the CryptGetHashParam function.

Normal applications should never set this parameter. In fact, some CSPs may not even support this capability. Occasionally though, it is convenient to sign a hash value that has been generated elsewhere. This is the usual sequence of operations:

1. The application creates a hash object with CryptCreateHash.

2. It specifies a hash value by setting the HP_HASHVAL parameter.

3. It signs the hash value using CryptSignHash, obtaining a digital signature block.

   Because the binding between the hashed data and the signature is fairly tenuous, no description string can be passed into CryptSignHash in this situation.

4. It destroys the hash object using CryptDestroyHash.

Note that some CSP types may add additional parameters that can be set with this function.

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.

Example

This function is used in a way similar to the CryptSetKeyParam function.

See Also

CryptCreateHash, CryptDestroyHash, CryptGetHashParam, CryptSetKeyParam, CryptSignHash