The Java TM Tutorial

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Trail: Security in JDK 1.2
Lesson: Generating and Verifying Signatures

## Prepare Initial Program Structure

> Here's the basic structure of the `VerSig` program created in the following parts of this lesson. Place this program structure in a file called `VerSig.java`.

>     import java.io.*;
>     import java.security.*;
>     import java.security.spec.*;

>     class VerSig {

>         public static void main(String[] args) {

>             /* Verify a DSA signature */

>             if (args.length != 3) {
>                 System.out.println("Usage: VerSig publickeyfile signaturefile datafile");
>                 }
>             else try{

>             // the rest of the code goes here

>             } catch (Exception e) {
>                 System.err.println("Caught exception " + e.toString());
>             }
>         }

>     }

> Notes:
> - The methods for verifying data are in the `java.security` package, so the program imports everything from that package. The program also imports the `java.io` package for methods needed to input the file data to be signed, as well as the `java.security.spec` package, which contains the `X509EncodedKeySpec` class.

> - Three arguments are expected, specifying the public key, the signature, and the data files.

> - The code written in subsequent steps of this lesson will go between the `try` and the `catch` blocks.

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