北大Java 语言程序设计 ppt课件及源码

				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());				        }								    }								}