How to use Crypto API in your ASP projects.

• Download demo project - 148 Kb

Summary

This application uses ATL, MFC, ASP and Crypt API. It will demonstrate how to make an ATL project that provides 2 cryptographic functions, how to use this component in your ASP projects, and how to register the component in MTS. The article also contains a GUI client console for directly testing the cryptographic functions.

This component can be used in Visual Basic, Access or Microsoft SQL.

Introduction

Recently I worked for a financial project regarding the Greek, Cyprus and Romanian stock exchange (www.greekmarkets.com, http://reporter.fasma.ro ). The project was coded mostly using ASP and VB COM, and a few ATL components as a middle tier over a SQL database. The middle tier component that I programmed was built with ATL and uses Crypto API. The idea consists in providing the encrypted data to HTTP, data which is useful for ASP pages. Because of HTTP transport the data is coded in a hexadecimal format.

Overview

First of all, I will show you how to use an ATL-control and how to provide methods that interrogate our component.

• Create a new ATL COM AppWizard project.

• Choose Dynamic Link Library (DLL) in the Server Type and check Support MFC and MTS.

  

• Add a new ATL object to your classes. Choose Objects->Simple Object from your ATL Object Wizard.

  

• In the attributes tab page choose Free option in Threading Model.

  

• Now we have a very nice component. It is more important to provide data to other programs by methods or properties. Unfortunately, the Microsoft wizard is a little poor and the user must input manually each parameter and its type.

  

Details

The simplest way to use cryptographic API and to encrypt your messages is the following:

    // Get handle to user default provider.

         CryptAcquireContext(&hProv, NULL, NULL, PROV_RSA_FULL, 0)

This function returns a handle to a particular CSP which includes the specification of a particular key container within the CSP. This key container is either a specifically requested key container or it is the default key container for the currently logged-on user. Note that the second and the third parameters are NULL. This means that our code will generate the same key all the time, independently of the current logged user, and/or if the encrypt was done on a computer and the decrypt on another one.

����// Create hash object.

����     CryptCreateHash(hProv, CALG_MD5, 0, 0, &hHash)

����// Hash password string.

����     CryptHashData(hHash, (BYTE *)szLocalPassword, dwLength, 0)

����// Create block cipher session key based on hash of the password.

����     CryptDeriveKey(hProv, CALG_RC4, hHash, CRYPT_EXPORTABLE, &hKey)

����// Encrypt data

����     CryptEncrypt(hKey, 0, TRUE, 0, pbBuffer, &dwLength, dwLength)

����// Coding the result in hexadecimal format

����     HtoA(dest, szPassword, sizeof(TCHAR)*_tcslen(dest) )

It is very easy to use the component in ASP pages (the same in Visual Basic, Access or Microsoft SQL):

 dim myOEncrypt
 dim src, dest

 set myOEncrypt   = Server.CreateObject("EncryptionATL.Encryption.1")


src = "CryptoAPI"
Response.Write "src: "
Response.Write src

Response.Write "Crypt: "
dest = myOEncrypt.Crypt(src)
Response.Write dest

Response.Write "LastError: "
Response.Write myOEncrypt.LastError

Response.Write "Decrypt: "
src = myOEncrypt.Decrypt(dest)
Response.Write src

Response.Write "LastError: "
Response.Write myOEncrypt.LastError

set myOEncrypt = nothing

Installation

• Copy the DLL under a directory with system execute privilege and register it with regsvr32 command or put it on the MTS. This way is better because if we want to modify the component and register it again, this is possible without restarting the computer - like in cases when using regsvr32 command that "blocks" your dll file.

• Open the MTS console (if you have NT4) or Component service (Windows 2000). In Computers -> My Computer->COM+ Application choose NewApplication. Give it a name, for example "Crypt";

  

• In the new Crypt COM+ application create a new component:

  

• And choose your crypto dll file:

  

• To modify the properties of the new created component right-click on it:

  

• Use directly the dialog console. Input some string in the edit box and click on the button!

• Copy the directory with asp pages under Web - and just try it !

Note

The program was designed as to use only small strings, with some digits (id's from tables). If you want more, you have to modify the component.