Mengenkripsi Pesan

Contoh berikut menunjukkan pesan yang sedang dienkripsi sebelum dikirim ke komputer jarak jauh melalui koneksi aman.

Contohnya mengasumsikan bahwa variabel SecHandle bernama phContext dan SOCKET bernama s diinisialisasi. Untuk deklarasi dan inisialisasi variabel ini, lihat Menggunakan SSPI dengan Windows Sockets Client dan Menggunakan SSPI dengan Windows Sockets Server. Contoh ini mencakup panggilan ke fungsi di Secur32.lib, yang harus disertakan di antara pustaka tautan.

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

SecPkgContext_StreamSizes  Sizes;
SECURITY_STATUS            scRet;
SecBufferDesc              Message;
SecBuffer                  Buffers[4];
SecBuffer                  *pDataBuffer;

PBYTE                       pbIoBuffer;
DWORD                       cbIoBuffer;
DWORD                       cbIoBufferLength;
PBYTE                       pbMessage;
DWORD                       cbMessage;

//--------------------------------------------------------------------
// Get the stream encryption sizes. This needs to 
// be done once per connection. 
// phContext must have been initialized during the handshake process.

scRet = QueryContextAttributes(
            phContext,
            SECPKG_ATTR_STREAM_SIZES,
            &Sizes);

if(FAILED(scRet))
{
    MyHandleError("Error reading SECPKG_ATTR_STREAM_SIZES");
}

//--------------------------------------------------------------------
// Allocate a working buffer. The plaintext sent to EncryptMessage
// can never be more than 'Sizes.cbMaximumMessage', so a buffer 
// size of Sizes.cbMaximumMessage plus the header and trailer sizes 
// is sufficient for the longest message.

cbIoBufferLength = Sizes.cbHeader + 
                   Sizes.cbMaximumMessage +
                   Sizes.cbTrailer;

if(!(pbIoBuffer = malloc((BYTE *), cbIoBufferLength)))
{
    MyHandleError("Out of memory");
}

//--------------------------------------------------------------------
// Create a plaintext message to be encrypted offset into the data 
// buffer by "header size" bytes. This allows encryption in place.

pbMessage = pbIoBuffer + Sizes.cbHeader;

StringCbPrintfA(pbMessage,
                cbIoBufferLength - Sizes.cbHeader,
                "This is the plaintext message.");
cbMessage = strlen(pbMessage);

//--------------------------------------------------------------------
// Encrypt the plaintext message.

Buffers[0].pvBuffer     = pbIoBuffer;
Buffers[0].cbBuffer     = Sizes.cbHeader;
Buffers[0].BufferType   = SECBUFFER_STREAM_HEADER;

Buffers[1].pvBuffer     = pbMessage;
Buffers[1].cbBuffer     = cbMessage;
Buffers[1].BufferType   = SECBUFFER_DATA;

Buffers[2].pvBuffer     = pbMessage + cbMessage;
Buffers[2].cbBuffer     = Sizes.cbTrailer;
Buffers[2].BufferType   = SECBUFFER_STREAM_TRAILER;

Buffers[3].BufferType   = SECBUFFER_EMPTY;

Message.ulVersion       = SECBUFFER_VERSION;
Message.cBuffers        = 4;
Message.pBuffers        = Buffers;

scRet = EncryptMessage(phContext, 0, &Message, 0);

if(FAILED(scRet))
{
    MyHandleError("Error returned by EncryptMessage.");
}

//--------------------------------------------------------------------
// Send the encrypted data.

if(!(SendMsg(
     s,
     pbIoBuffer,
     Buffers[0].cbBuffer + Buffers[1].cbBuffer + 
           Buffers[2].cbBuffer)))
{
     MyHandleError("SendMsg failed.");
}