CryptHashMessage function

The CryptHashMessage function creates a hash of the message.

Syntax

BOOL CryptHashMessage(
  PCRYPT_HASH_MESSAGE_PARA pHashPara,
  BOOL                     fDetachedHash,
  DWORD                    cToBeHashed,
  const BYTE * []          rgpbToBeHashed,
  DWORD []                 rgcbToBeHashed,
  BYTE                     *pbHashedBlob,
  DWORD                    *pcbHashedBlob,
  BYTE                     *pbComputedHash,
  DWORD                    *pcbComputedHash
);

Parameters

pHashPara

A pointer to a CRYPT_HASH_MESSAGE_PARA structure that contains the hash parameters.

fDetachedHash

If this parameter is set to TRUE, only pbComputedHash is encoded in pbHashedBlob. Otherwise, both rgpbToBeHashed and pbComputedHash are encoded.

cToBeHashed

The number of array elements in rgpbToBeHashed and rgcbToBeHashed. This parameter can only be one unless fDetachedHash is set to TRUE.

rgpbToBeHashed

An array of pointers to buffers that contain the contents to be hashed.

rgcbToBeHashed

An array of sizes, in bytes, of the buffers pointed to by rgpbToBeHashed.

pbHashedBlob

A pointer to a buffer to receive the hashed message encoded for transmission.

This parameter can be NULL if the hashed message is not needed for additional processing or to set the size of the hashed message for memory allocation purposes. A hashed message will not be returned if this parameter is NULL. For more information, see Retrieving Data of Unknown Length.

pcbHashedBlob

A pointer to a DWORD that specifies the size, in bytes, of the buffer pointed to by the pbHashedBlob parameter. When the function returns, this variable contains the size, in bytes, of the decrypted message copied to pbHashedBlob. This parameter must be the address of a DWORD and not NULL or the length of the buffer will not be returned.

Note  When processing the data returned, 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 will fit 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.
 

pbComputedHash

A pointer to a buffer to receive the newly created hash value. This parameter can be NULL if the newly created hash is not needed for additional processing, or to set the size of the hash for memory allocation purposes. For more information, see Retrieving Data of Unknown Length.

pcbComputedHash

A pointer to a DWORD that specifies the size, in bytes, of the buffer pointed to by the pbComputedHash parameter. When the function returns, this DWORD contains the size, in bytes, of the newly created hash that was copied to pbComputedHash.

Note  When processing the data returned, 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 will fit 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.
 

Return value

If the function succeeds, the function returns nonzero (TRUE).

If the function fails, it returns zero (FALSE). For extended error information, call GetLastError.

Note  Errors from the called functions CryptCreateHash, CryptHashData, and CryptGetHashParam might be propagated to this function.
 
The GetLastError function returns the following error codes most often.
Return code Description
E_INVALIDARG
The message encoding type is not valid. Currently only PKCS_7_ASN_ENCODING is supported. The cbSize in *pHashPara is not valid.
ERROR_MORE_DATA
If the buffer specified by the pbHashedBlob parameter is not large enough to hold the returned data, the function sets the ERROR_MORE_DATA code and stores the required buffer size, in bytes, into the variable pointed to by pbHashedBlob.
 

If the function fails, GetLastError may return an Abstract Syntax Notation One (ASN.1) encoding/decoding error. For information about these errors, see ASN.1 Encoding/Decoding Return Values.

Requirements

   
Minimum supported client Windows XP [desktop apps only]
Minimum supported server Windows Server 2003 [desktop apps only]
Target Platform Windows
Header wincrypt.h
Library Crypt32.lib
DLL Crypt32.dll

See also

CryptVerifyDetachedMessageHash

CryptVerifyMessageHash

Simplified Message Functions