Summary | in Visual Basic .NET

Making Quick Response Code in Visual Basic .NET Summary |

easy-to-use class unless you are building and distributing design-time controls. For the rest of us, it s make-it-up-as-you-go time. Fortunately, .NET has great support tools, so adding licensing support isn t too difficult.

In this chapter s project code, we ll follow two of the four licensing steps discussed in the section The Library Licensing System, earlier in this chapter: generating the license file and using the license file. The design we created previously is good enough for our needs, although we still need to record it in the project s technical documentation. We won t formally install the license file until we create the setup program in 25.

Since we ll be adding a new external file that will be processed by the Library Project, we need to document its structure in the project s Technical Resource Kit. Let s add the following new section to that document.

The Library Project reads a customer-specific license file generated by the Library License Generation support application. That program generates a digitally signed XML license file that includes licensee information. Here is a sample of the license file content:

< xml version="1.0" > <License> <Product>Library Project</Product> <LicenseDate>1/1/2000</LicenseDate> <ExpireDate>12/31/2999</ExpireDate> <CoveredVersion>1.*</CoveredVersion> <Licensee>John Q. Public</Licensee> <SerialNumber>LIB-123456789</SerialNumber> <Signature> Digital signature appears here (not shown) </Signature> </License>

The <LicenseDate> and <ExpireDate> tags indicate the first and last valid dates of the license. <Licensee> indicates the name of the license owner. <SerialNumber> includes the vendor-defined serial number associated with this license. The <CoveredVersion> tag contains data similar to the assembly version number included in .NET applications. It has up to four dot-delimited parts:

Each component can include a number from 0 to 9999, or the * character, which indicates all valid values for that position.

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The <Signature> section contains the generated digital signature. Its format is dependant on the XML Cryptography tools in .NET that generate this section. To ensure a proper digital signature, always use the Library License Generation support application to build license files. That support application generates a public and private key pair for use in digital signing. The public portion of this key (as an XML file) must be added as a resource named LicensePublicKey to the Library application. The private portion must be kept private. For consistency, the same key pair should be used throughout the lifetime of the Library Project s availability. We will also store the location of the license file as an application setting in the main program. We need to record that setting with the other application settings already added to the User Settings section of the Resource Kit.

The path to the Library License file on this workstation. If not supplied, the program will look for a file named LibraryLicense.lic in the same folder as the application.

Generating license files and digital signatures by hand using Notepad would be...well, let s not even think about it. Instead, we ll depend on a custom application to create the files and signatures for us. I ve already developed that custom tool for you. You ll find it in the installation directory for this book s code, in the LibraryLicensing subdirectory. This support application includes two main forms. The first (KeyLocationForm.vb, shown in Figure 22-6) locates or creates the public-private key files used in the digital signature process.

Most of the form s code helps to locate and verify the folder that will contain the two key files (one private, one public). Some of the code in the ActGenerate_Click event handler creates the actual files.

Dim twoPartKey As RSA Dim publicFile As String Dim privateFile As String ...some code skipped here, then... ' ----- Generate the keys. twoPartKey = New RSACryptoServiceProvider twoPartKey = RSA.Create( ) ' ----- Save the public key. My.Computer.FileSystem.WriteAllText(publicFile, _ twoPartKey.ToXmlString(False), False) ' ----- Save the private key. My.Computer.FileSystem.WriteAllText(privateFile, _ twoPartKey.ToXmlString(True), False)

That s really simple! The System.Security.Cryptography.RSA class and the related RSACryptoServiceProvider class do all the work. All you have to do is call the RSA.Create method, and then generate the relevant XML keys using the ToXmlString method, passing an argument of False for the public key and True for the private key. If you want to look at some sample keys, open the LicenseFiles subdirectory in this book s source installation directory. You ll find two files, one for the public key and one for the private key. I d print one of them here, but it all just looks like random characters. The other support form is MainForm.vb, which generates the actual end-user license file, and appears in Figure 22-7.

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