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Posted 12 Aug 2002

.NET Symmetric File Encryption Object

, 13 Aug 2002
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File encryption object using Managed Extensions for C++
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I would have paid a month's worth of salary to get a library as extensive as the .NET Framework class library. The reason why I say that is because using the .NET Framework library, I can easily shave off weeks in development time on a single project. But, as with any other library you still need to develop your own objects to abstract the complexity of the underlying framework. The .NET Framework is no exception.

The CCrypto object I am demonstrating shows how to use the .NET Framework Cryptographic Service classes to encrypt and decrypt files. This article documents the object, and includes code samples on implementing it.

With anything new there is a learning curve. For me, the .NET Framework and Managed Extensions for C++ does not change that rule. With encryption near and dear to my heart I decided to begin developing crypto objects that hide the complexity of the framework, this article shows how easy it is done.

This article is the first in a three part series on symmetric encryption with the .NET Framework using Managed Extensions for C++. I'll follow this article with a command line utility implementing the object, and an article covering an overview of symmetric encryption and the classes in the .NET Cryptographic Services.

You will need the Visual C++.NET to compile and test the code. I have assumed you are familiar with Managed Extensions for C++.

The CCrypto Object

The purpose of CCrypto is to abstract all the .NET Framework classes to encrypt, decrypt, wipe, and fingerprint (hash) files.

To use the CCrypto object you need to include the definition header for the object and reference the namespace. The CCrypto object consumes any derived encryption algorithm of the SymmetricAlgorithm class. When encrypting or decrypting, you also need to consume a HashAlgorithm derived class for hashing.

The selection of the hashing function must have a similar key space as the encryption function. So, if you are using RC2 which produces uses a 128 bit key, use the MD5CryptoServiceProvider() object which has a 128 bit key space. Mix and matching the key spaces with throw an exception.

The CCrypto object does not directly use the passphrase or key file as the encryption key. Rather, it creates a hash of the passphrase or key file and uses the hash as the key.

The object's definition and implementation code is listed after the code snippets demonstrating the use of the object.


I am not aware of any issues with the object. I was not able to find any test vectors to test Microsoft's implementation of the symmetric encryption algorithms. I have also not tested the quality of the cryptographic random number generator. I would have liked it if the encryption / decryption worked faster. With my P4 1.6Ghz, ATA100 drive, XP Pro, I achieved 7.6 Mb/s encryption on a 20 Mb file using the RC2 algorithm.


CCrypto (SymmetricAlgorithm * CryptoServiceProvider, HashAlgorithm * HashServiceProvider);
CCrypto (HashAlgorithm * HashServiceProvider);
CCrypto ()

Public Methods

Encrypt Encrypts a file
Decrypt Decrypts a file
WipeFileSecurely removes the file
HashFile Gets the file's fingerprint
CreateKeyFile Creates a file with random data


get_HashProviderSets the hash provider
set_SetKeyPhraseSets the Key phrase for encryption/decryption
set_SetFileKeySets the Key file for encryption/decryption

Protected Methods

CryptPerforms the encryption/decryption
HandleExceptionException handler


<pre lang=mc++>bool Encrypt (String * inFilePath, String * OutfilePath) bool Decrypt (String * inFilePath, String * OutfilePath) bool WipeFile (String * inFilePath, int nWipes ) bool CreateKeyFile (String * outfilepath, unsigned int nBytes) Byte HashFile (String * inFile )[] bool Crypt (int Direction, String * inFilePath, String * OutfilePath); virtual void HandleException (Exception * e) __property void set_SetKeyPhrase (String * Phrase) __property HashAlgorithm * get_HashProvider () __property void set_HashProvider (HashAlgorithm * myHashServiceProvider) __property void set_SetFileKey (String * FileKeyPath)

Code Examples

I have referenced the namespaces of System::Security::Cryptography and MyCrypto so that the samples are more readable. To use the object, you need to include the Crypto.h header. Below is an example of the include and namespace references. <pre lang=mc++>#using <system.dll> #include "Crypto.h" using namespace System::Security::Cryptography ; using namespace MyCrypto ; This code snippet to retrieve a file's fingerprint and displays that to the console. <pre lang=mc++>CCrypto * myCrypto = new CCrypto (new MD5CryptoServiceProvider()); Console::WriteLine( BitConverter::ToString (myCrypto->HashFile ("c:\\encnotes2.txt")) ); This code example creates a file with random data to be used as a key. The random data comes from the random number generator that is part of the .NET Cryptographic Services. This is the preferred way to encrypt the data. The key file can reside on disk, smart card, or USB key. <pre lang=mc++>CCrypto * myCrypto = new CCrypto (); // Create key file of c:\mykey.key with 512 bytes of random data myCrypto->CreateKeyFile ("c:\\mykey.key",512); This example demonstrates how to wipe a file that is no longer needed. Before deleting the file from the device the file will be over written with ten patterns. <pre lang=mc++>CCrypto * myCrypto = new CCrypto (); // Wipe file with 10 patterns before deleting myCrypto->WipeFile ("c:\\PersonalNotes.txt",10); Encrypting a file using the 256 bit Rijndael algorithm and a file key. <pre lang=mc++>CCrypto * myCrypto = new CCrypto (new RijndaelManaged(),new SHA256Managed()); myCrypto->CreateKeyFile ("c:\\mykey.key",512); myCrypto->SetFileKey = "c:\\mykey.key"; myCrypto->Encrypt ("c:\\PersonalNotes.txt","c:\\PersonalNotes.txt.enc"); To decrypt the file we need to use the same algorithm and key. <pre lang=mc++>CCrypto * myCrypto = new CCrypto (new RijndaelManaged(),new SHA256Managed()); myCrypto->SetFileKey = "c:\\mykey.key"; myCrypto->Decrypt ("c:\\PersonalNotes.txt.enc","c:\\PersonalNotes.txt"); Here is an example of encrypting a file using a phrase. <pre lang=mc++>CCrypto * myCrypto = new CCrypto (new RijndaelManaged(),new SHA256Managed()); myCrypto->SetKeyPhrase = S"You can place any valid string here."; myCrypto->Encrypt ("c:\\PersonalNotes.txt","c:\\PersonalNotes.txt.enc");

I am interested in hearing what you have to say regarding the CCrypto object or this article. If you have any questions, comments, or criticisms, don't hesitate to let me know.


This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here


About the Author

Bill Ferreira
Web Developer
Canada Canada
No Biography provided

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Comments and Discussions

GeneralHi Pin
NapCrisis24-Sep-08 22:26
memberNapCrisis24-Sep-08 22:26 
GeneralFilename scrambling Pin
lyris1-Sep-08 9:40
memberlyris1-Sep-08 9:40 
Generalerror C3828: 'MyCrypto::CCrypto': placement arguments not allowed while creating instances of managed classes Pin
nlesser15-Jul-04 11:39
sussnlesser15-Jul-04 11:39 
GeneralRe: error C3828: 'MyCrypto::CCrypto': placement arguments not allowed while creating instances of managed classes Pin
nlesser15-Jul-04 13:29
sussnlesser15-Jul-04 13:29 
GeneralPassword and encryption key Pin
Bing Xue25-Mar-04 3:17
memberBing Xue25-Mar-04 3:17 
QuestionIs WipeFile really wiping? Pin
Drizz't15-Sep-03 18:21
memberDrizz't15-Sep-03 18:21 
AnswerRe: Is WipeFile really wiping? Pin
Bill Ferreira16-Sep-03 11:56
memberBill Ferreira16-Sep-03 11:56 
GeneralRe: Is WipeFile really wiping? Pin
Anonymous21-Sep-03 18:15
sussAnonymous21-Sep-03 18:15 
GeneralMissing Source ZIP Pin
Jubjub13-Aug-02 13:55
memberJubjub13-Aug-02 13:55 

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