CryptMsgUpdate function (wincrypt.h)

The CryptMsgUpdate function adds contents to a cryptographic message. The use of this function allows messages to be constructed piece by piece through repetitive calls of CryptMsgUpdate. The added message content is either encoded or decoded depending on whether the message was opened with CryptMsgOpenToEncode or CryptMsgOpenToDecode.

Syntax

BOOL CryptMsgUpdate(
  [in] HCRYPTMSG  hCryptMsg,
  [in] const BYTE *pbData,
  [in] DWORD      cbData,
  [in] BOOL       fFinal
);

Parameters

[in] hCryptMsg

Cryptographic message handle of the message to be updated.

[in] pbData

A pointer to the buffer holding the data to be encoded or decoded.

[in] cbData

Number of bytes of data in the pbData buffer.

[in] fFinal

Indicates that the last block of data for encoding or decoding is being processed. Correct usage of this flag is dependent upon whether the message being processed has detached data. The inclusion of detached data in a message is indicated by setting dwFlags to CMSG_DETACHED_FLAG in the call to the function that opened the message.

If CMSG_DETACHED_FLAG was not set and the message was opened using either CryptMsgOpenToDecode or CryptMsgOpenToEncode, fFinal is set to TRUE, and CryptMsgUpdate is only called once.

If the CMSG_DETACHED_FLAG flag was set and a message is opened using CryptMsgOpenToEncode, fFinal is set to TRUE only on the last call to CryptMsgUpdate.

If the CMSG_DETACHED_FLAG flag was set and a message is opened using CryptMsgOpenToDecode, fFinal is set to TRUE when the header is processed by a single call to CryptMsgUpdate. It is set to FALSE while processing the detached data in subsequent calls to CryptMsgUpdate until the last detached data block is to be processed. On the last call to CryptMsgUpdate, it is set to TRUE.

When detached data is decoded, the header and the content of a message are contained in different BLOBs. Each BLOB requires that fFinal be set to TRUE when the last call to the function is made for that BLOB.

Return value

If the function succeeds, the return value is nonzero (TRUE).

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

Errors encountered in the application defined callback function specified by pStreamInfo in CryptMsgOpenToDecode and CryptMsgOpenToEncode might be propagated to CryptMsgUpdate if streaming is used. If this happens, SetLastError is not called by CryptMsgUpdate after the callback function returns, which preserves any errors encountered under the control of the application. It is the responsibility of the callback function (or one of the APIs that it calls) to call SetLastError if an error occurs while the application is processing the streamed data.

The following table lists the error codes most commonly returned by the GetLastError function.

Propagated errors might be encountered from any of the following functions:

• CryptHashData
• CryptGetHashParam
• CryptSignHash
• CryptGetKeyParam
• CryptEncrypt
• CryptCreateHash

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

See also

CryptMsgGetParam

CryptMsgOpenToDecode

CryptMsgOpenToEncode

Low-level Message Functions

Simplified Message Functions