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copied!<p>Once you get in the groove of things, CryptoAPI is relatively straightforward to use. The problem is doing it in a way that is compatible with other cryptography libraries (including .NET framework). I have successfully done this before, but it has been a while; the major sticking point is figuring out how to convert a plain text key into a format usable with CryptoAPI (which operates with "key blobs"). Luckily Microsoft has given us <a href="http://support.microsoft.com/kb/228786" rel="nofollow noreferrer">a working, if tedious, example</a>. As for the CryptoAPI way of doing things, here is an example:</p> <pre><code>// 1. acquire a provider context. // the Microsoft Enhanced provider offers the Triple DES algorithm. HCRYPTPROV hProv = NULL; if(CryptAcquireContext(&hProv, NULL, MS_ENHANCED_PROV, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT)) { // 2. generate the key; see Microsoft KB link above on how to do this. HKEY hKey = NULL; if(ImportPlainTextSessionKey(hProv, lpKeyData, cbKeyData, CALG_3DES, &hKey)) { // 3. set the IV. if(CryptSetKeyParam(hKey, KP_IV, lpIVData, 0)) { // 4. read the encrypted data from the source file. DWORD cbRead = 0; while(ReadFile(hSourceFile, buffer, 8192, &cbRead, NULL) && cbRead) { // 5. decrypt the data (in-place). BOOL bFinal = cbRead < 8192 ? TRUE : FALSE; DWORD cbDecrypted = 0; if(CryptDecrypt(hKey, NULL, bFinal, 0, buffer, &cbDecrypted)) { // 6. write the decrypted data to the destination file. DWORD cbWritten = 0; WriteFile(hDestFile, buffer, cbDecrypted, &cbWritten, NULL); } } } CryptDestroyKey(hKey); hKey = NULL; } CryptReleaseContext(hProv, 0); hProv = NULL; } </code></pre>

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