CryptHashData function

The CryptHashData function adds data to a specified hash object. This function and CryptHashSessionKey can be called multiple times to compute the hash of long or discontinuous data streams.

Before calling this function, CryptCreateHash must be called to create a handle of a hash object.

Syntax

BOOL WINAPI CryptHashData(
  _In_ HCRYPTHASH hHash,
  _In_ BYTE       *pbData,
  _In_ DWORD      dwDataLen,
  _In_ DWORD      dwFlags
);

Parameters

hHash [in]

Handle of the hash object.

pbData [in]

A pointer to a buffer that contains the data to be added to the hash object.

dwDataLen [in]

Number of bytes of data to be added. This must be zero if the CRYPT_USERDATA flag is set.

dwFlags [in]

The following flag values are defined.

Value	Meaning
CRYPT_OWF_REPL_LM_HASH 0x00000001	This flag is not used.
CRYPT_USERDATA 1 (0x1)	All Microsoft Cryptographic Providers ignore this parameter. For any CSP that does not ignore this parameter, if this flag is set, the CSP prompts the user to input data directly. This data is added to the hash. The application is not allowed access to the data. This flag can be used to allow the user to enter a PIN into the system.

 

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

The following example shows adding data to a specified hash object already created by CryptCreateHash. For an example that includes the complete context for this example, see Example C Program: Signing a Hash and Verifying the Hash Signature. For another example that uses this function, see Example C Program: Deriving a Session Key from a Password.

//-------------------------------------------------------------
// Declare and initialize variables.

BYTE *pbBuffer= (BYTE *)"The data that is to be hashed and signed.";
DWORD dwBufferLen = strlen((char *)pbBuffer)+1;

//--------------------------------------------------------------------
//  This code assumes that the handle of a cryptographic context 
//  has been acquired and that a hash object has been created 
//  and its handle (hHash) is available.


if(CryptHashData(
   hHash, 
   pbBuffer, 
   dwBufferLen, 
   0)) 
{
     printf("The data buffer has been added to the hash.\n");
}
else
{
     printf("Error during CryptHashData.\n");
     exit(1);
}
//--------------------------------------------------------------------
//  At this point, the content of pbBuffer has been added to the hash.
//  Additional data can be added by repeatedly calling CryptHashData.
//  When the hash object is no longer needed, it should be destroyed.

if(hHash) 
  CryptDestroyHash(hHash);

Requirements

See also

Hash and Digital Signature Functions

CryptCreateHash

CryptHashSessionKey

CryptSignHash