The Java TM Tutorial

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Trail: Security in JDK 1.1
Lesson: Using the Security API to Generate and Verify a Signature

## Step 5: Compile the Program

> You have now created the complete `testSig.java` program. Use the Java compiler to compile it.

> Here's the full source code, with some comments added:

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

> >     class testSig {

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

> >             /* Test generating and verifying a DSA signature */

> >             try {

> >                 /* generate a key pair */

> >                 KeyPairGenerator keyGen = KeyPairGenerator.getInstance("DSA");
> >                 keyGen.initialize(1024, new SecureRandom());
> >                 KeyPair pair = keyGen.generateKeyPair();

> >                 /* create a Signature object to use
> >                  * for signing and verifying */

> >                 Signature dsa = Signature.getInstance("SHA/DSA");

> >                 /* initialize the Signature object for signing */

> >                 PrivateKey priv = pair.getPrivate();

> >                 dsa.initSign(priv);

> >                 /* Update and sign the data */

> >                 FileInputStream fis = new FileInputStream(args[0]);
> >                 byte b;
> >                 while (fis.available() != 0) {
> >                     b = (byte) fis.read();
> >                     dsa.update(b);
> >                     };

> >                 fis.close();

> >                 /* Now that all the data to be signed
> >                  * has been read in, sign it */
> >                 byte[] sig = dsa.sign();

> >                 /* Verify the signature */

> >                 /* Initialize the Signature object for verification */
> >                 PublicKey pub = pair.getPublic();
> >                 dsa.initVerify(pub);

> >                 /* Update and verify the data */

> >                 fis = new FileInputStream(args[0]);
> >                 while (fis.available() != 0) {
> >                     b = (byte) fis.read();
> >                     dsa.update(b);
> >                     };

> >                 fis.close();

> >                 boolean verifies = dsa.verify(sig);

> >                 System.out.println("signature verifies: " + verifies);

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

> >         }

> >     }

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