範例 C 程式：編碼和解碼資料
下列範例會編碼和解碼簡單、一般資料，並說明下列工作和 CryptoAPI 函式。
- 使用 CryptMsgCalculateEncodedLength判斷緩衝區保存編碼資料所需的長度。
- 使用 CryptMsgOpenToEncode開啟訊息進行編碼。
- 使用 CryptMsgUpdate將內容新增至編碼的訊息。
- 使用 CryptMsgGetParam將編碼的訊息複製到緩衝區。
- 使用 CryptMsgClose關閉編碼的訊息。
- 開啟訊息以使用 CryptMsgOpenToDecode 解碼。
- 使用 CryptMsgUpdate 和 CryptMsgGetParam 來取得解碼的資料。
此範例使用 MyHandleError函式。 此函式的程式碼隨附于範例中。 此函式和其他輔助函式的程式碼也會列在常規用途 Functions底下。
//-------------------------------------------------------------------
// Copyright (C) Microsoft. All rights reserved.
// Example of encoding and decoding a message.
#pragma comment(lib, "crypt32.lib")
#include <stdio.h>
#include <windows.h>
#include <Wincrypt.h>
#define MY_ENCODING_TYPE (PKCS_7_ASN_ENCODING | X509_ASN_ENCODING)
void MyHandleError(char *s);
void main(void)
{
//-------------------------------------------------------------------
// Declare and initialize variables. This includes getting a pointer
// to the message content. This sample program creates the message
// content and gets a pointer to it. In most situations,
// the content will exist somewhere and a pointer to it
// will get passed to the application.
HCRYPTMSG hMsg;
BYTE* pbContent; // a byte pointer to the message
DWORD cbContent; // the size of message
DWORD cbEncodedBlob;
BYTE *pbEncodedBlob;
//-------------------------------------------------------------------
// The following variables are used only in the decoding phase.
DWORD cbDecoded;
BYTE *pbDecoded;
//-------------------------------------------------------------------
// Begin processing. Display the original message.
pbContent = (BYTE*) "Security is our only business";
cbContent = strlen((char *) pbContent)+1;
printf("The original message => %s\n",pbContent);
//-------------------------------------------------------------------
// Get the size of the encoded message BLOB.
if(cbEncodedBlob = CryptMsgCalculateEncodedLength(
MY_ENCODING_TYPE, // message encoding type
0, // flags
CMSG_DATA, // message type
NULL, // pointer to structure
NULL, // inner content object ID
cbContent)) // size of content
{
printf("The length of the data has been calculated. \n");
}
else
{
MyHandleError("Getting cbEncodedBlob length failed");
}
//-------------------------------------------------------------------
// Allocate memory for the encoded BLOB.
if(pbEncodedBlob = (BYTE *) malloc(cbEncodedBlob))
{
printf("Memory has been allocated for the signed message. \n");
}
else
{
MyHandleError("Memory allocation failed");
}
//-------------------------------------------------------------------
// Open a message to encode.
if(hMsg = CryptMsgOpenToEncode(
MY_ENCODING_TYPE, // encoding type
0, // flags
CMSG_DATA, // message type
NULL, // pointer to structure
NULL, // inner content object ID
NULL)) // stream information (not used)
{
printf("The message to be encoded has been opened. \n");
}
else
{
MyHandleError("OpenToEncode failed");
}
//-------------------------------------------------------------------
// Update the message with the data.
if(CryptMsgUpdate(
hMsg, // handle to the message
pbContent, // pointer to the content
cbContent, // size of the content
TRUE)) // last call
{
printf("Content has been added to the encoded message. \n");
}
else
{
MyHandleError("MsgUpdate failed");
}
//-------------------------------------------------------------------
// Get the resulting message.
if(CryptMsgGetParam(
hMsg, // handle to the message
CMSG_BARE_CONTENT_PARAM, // parameter type
0, // index
pbEncodedBlob, // pointer to the BLOB
&cbEncodedBlob)) // size of the BLOB
{
printf("Message encoded successfully. \n");
}
else
{
MyHandleError("MsgGetParam failed");
}
//-------------------------------------------------------------------
// pbEncodedBlob now points to the encoded, signed content.
//-------------------------------------------------------------------
// Close the message.
if(hMsg)
CryptMsgClose(hMsg);
//-------------------------------------------------------------------
// The following code decodes a message.
// This code may be included here or could be used
// in a stand-alone program if the message
// to be decoded and its size were input.
// The encoded message BLOB and its length could be read
// from a disk file or could be extracted from an email message
// or other input source.
//-------------------------------------------------------------------
// Open a message for decoding.
if(hMsg = CryptMsgOpenToDecode(
MY_ENCODING_TYPE, // encoding type.
0, // flags.
CMSG_DATA, // look for a data message.
NULL, // cryptographic provider.
NULL, // recipient information.
NULL)) // stream information.
{
printf("The message to decode is open. \n");
}
else
{
MyHandleError("OpenToDecode failed");
}
//-------------------------------------------------------------------
// Update the message with an encoded BLOB.
// Both pbEncodedBlob, the encoded data,
// and cbEncodedBlob, the length of the encoded data,
// must be available.
printf("\nThe length of the encoded message is %d.\n\n",
cbEncodedBlob);
if(CryptMsgUpdate(
hMsg, // handle to the message
pbEncodedBlob, // pointer to the encoded BLOB
cbEncodedBlob, // size of the encoded BLOB
TRUE)) // last call
{
printf("The encoded BLOB has been added to the message. \n");
}
else
{
MyHandleError("Decode MsgUpdate failed");
}
//-------------------------------------------------------------------
// Get the size of the content.
if(CryptMsgGetParam(
hMsg, // handle to the message
CMSG_CONTENT_PARAM, // parameter type
0, // index
NULL, // address for returned
// information
&cbDecoded)) // size of the returned
// information
{
printf("The decoded message size is %d. \n", cbDecoded);
}
else
{
MyHandleError("Decode CMSG_CONTENT_PARAM failed");
}
//-------------------------------------------------------------------
// Allocate memory.
if(pbDecoded = (BYTE *) malloc(cbDecoded))
{
printf("Memory has been allocated for the decoded message.\n");
}
else
{
MyHandleError("Decoding memory allocation failed.");
}
//-------------------------------------------------------------------
// Get a pointer to the content.
if(CryptMsgGetParam(
hMsg, // handle to the message
CMSG_CONTENT_PARAM, // parameter type
0, // index
pbDecoded, // address for returned
// information
&cbDecoded)) // size of the returned
// information
{
printf("The message is %s.\n",(LPSTR)pbDecoded);
}
else
{
MyHandleError("Decode CMSG_CONTENT_PARAM #2 failed");
}
//-------------------------------------------------------------------
// Clean up.
if(pbEncodedBlob)
free(pbEncodedBlob);
if(pbDecoded)
free(pbDecoded);
if(hMsg)
CryptMsgClose(hMsg);
printf("This program ran to completion without error. \n");
} // End of main
//-------------------------------------------------------------------
// This example uses the function MyHandleError, a simple error
// handling function, to print an error message and exit
// the program.
// For most applications, replace this function with one
// that does more extensive error reporting.
void MyHandleError(char *s)
{
printf("An error occurred in running the program.\n");
printf("%s\n",s);
printf("Error number %x\n.",GetLastError());
printf("Program terminating.\n");
exit(1);
}