CryptGetHashParam function

The CryptGetHashParam function retrieves data that governs the operations of a hash object. The actual hash value can be retrieved by using this function.

Syntax

BOOL WINAPI CryptGetHashParam(
  _In_    HCRYPTHASH hHash,
  _In_    DWORD      dwParam,
  _Out_   BYTE       *pbData,
  _Inout_ DWORD      *pdwDataLen,
  _In_    DWORD      dwFlags
);

Parameters

hHash [in]

Handle of the hash object to be queried.

dwParam [in]

Query type. This parameter can be set to one of the following queries.

Value	Meaning
HP_ALGID Hash algorithm	An ALG_ID that indicates the algorithm specified when the hash object was created. For a list of hash algorithms, see CryptCreateHash.
HP_HASHSIZE Hash value size	DWORD value indicating the number of bytes in the hash value. This value will vary depending on the hash algorithm. Applications must retrieve this value just before the HP_HASHVAL value so the correct amount of memory can be allocated.
HP_HASHVAL Hash value	The hash value or message hash for the hash object specified by hHash. This value is generated based on the data supplied to the hash object earlier through the CryptHashData and CryptHashSessionKey functions. The CryptGetHashParam function completes the hash. After CryptGetHashParam has been called, no more data can be added to the hash. Additional calls to CryptHashData or CryptHashSessionKey fail. After the application is done with the hash, CryptDestroyHash should be called to destroy the hash object.

 

Note  CSPs can add more values that this function can query.

 

pbData [out]

A pointer to a buffer that receives the specified value data. The form of this data varies, depending on the value number. This parameter can be NULL to determine the memory size required.

pdwDataLen [in, out]

A pointer to a DWORD value specifying the size, in bytes, of the pbData buffer. When the function returns, the DWORD value contains the number of bytes stored in the buffer. If pbData is NULL, set the value of pdwDataLen to zero.

Note  When processing the data returned in the buffer, applications must use the actual size of the data returned. The actual size can be slightly smaller than the size of the buffer specified on input. (On input, buffer sizes are usually specified large enough to ensure that the largest possible output data fits in the buffer.) On output, the variable pointed to by this parameter is updated to reflect the actual size of the data copied to the buffer.

 

dwFlags [in]

Reserved for future use and must be zero.

Return value

If the function succeeds, the return value is TRUE.

If the function fails, the return value is FALSE. For extended error information, call GetLastError.

The error codes prefaced by "NTE" are generated by the particular CSP you are using. Some possible error codes follow.

Examples

For an example that uses the CryptGetHashParam function, see Example C Program: Duplicating a Hash.

Requirements

See also

Hash and Digital Signature Functions

ALG_ID

CryptCreateHash

CryptDestroyHash

CryptGetKeyParam

CryptHashData

CryptHashSessionKey

CryptSetHashParam