DSA Batch Verification Algorithm

GenSig.java
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import java.io.*;
import java.security.*;

class GenSig {

    public static void main(String[] args) {
   //     args=new String[]{"LabelDemo.java"};
        /* Generate a DSA signature */

        if (args.length != 1) {
            System.out.println("Usage: GenSig nameOfFileToSign");
            }
        else try{

            /* Generate a key pair */

            KeyPairGenerator keyGen = KeyPairGenerator.getInstance("DSA", "SUN");
            SecureRandom random = SecureRandom.getInstance("SHA1PRNG", "SUN");

            keyGen.initialize(1024, random);

            KeyPair pair = keyGen.generateKeyPair();
            PrivateKey priv = pair.getPrivate();
            PublicKey pub = pair.getPublic();


            /* Create a Signature object and initialize it with the private key */

            Signature dsa = Signature.getInstance("SHA1withDSA", "SUN");

            dsa.initSign(priv);

            /* Update and sign the data */

            FileInputStream fis = new FileInputStream(args[0]);
            BufferedInputStream bufin = new BufferedInputStream(fis);
            byte[] buffer = new byte[1024];
            int len;
            while (bufin.available() != 0) {
                len = bufin.read(buffer);
                dsa.update(buffer, 0, len);
                };

            bufin.close();

            /* Now that all the data to be signed has been read in,
                    generate a signature for it */

            byte[] realSig = dsa.sign();

       
            /* Save the signature in a file */
            FileOutputStream sigfos = new FileOutputStream("sig");
            sigfos.write(realSig);

            sigfos.close();


            /* Save the public key in a file */
            byte[] key = pub.getEncoded();
            FileOutputStream keyfos = new FileOutputStream("suepk");
            keyfos.write(key);

            keyfos.close();
            System.out.println("Signature Generated");

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

    };

}






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Usage: GenSig nameOfFileToSign

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VerSig.java
--------------------

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

class VerSig {

    public static void main(String[] args) {

        /* Verify a DSA signature */
       // args =new String[]{"suepk","sig","1"};//LabelDemo.java"};
        if (args.length != 3) {
            System.out.println("Usage: VerSig publickeyfile signaturefile datafile");
            }
        else try{

            /* import encoded public key */

            FileInputStream keyfis = new FileInputStream(args[0]);
            byte[] encKey = new byte[keyfis.available()]; 
            keyfis.read(encKey);

            keyfis.close();

            X509EncodedKeySpec pubKeySpec = new X509EncodedKeySpec(encKey);

            KeyFactory keyFactory = KeyFactory.getInstance("DSA", "SUN");
            PublicKey pubKey = keyFactory.generatePublic(pubKeySpec);

            /* input the signature bytes */
            FileInputStream sigfis = new FileInputStream(args[1]);
            byte[] sigToVerify = new byte[sigfis.available()];
            sigfis.read(sigToVerify );

            sigfis.close();

            /* create a Signature object and initialize it with the public key */
            Signature sig = Signature.getInstance("SHA1withDSA", "SUN");
            sig.initVerify(pubKey);

            /* Update and verify the data */

            FileInputStream datafis = new FileInputStream(args[2]);
            BufferedInputStream bufin = new BufferedInputStream(datafis);

            byte[] buffer = new byte[1024];
            int len;
            while (bufin.available() != 0) {
                len = bufin.read(buffer);
                sig.update(buffer, 0, len);
                };

            bufin.close();


            boolean verifies = sig.verify(sigToVerify);

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


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

    }

}
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Usage: VerSig publickeyfile signaturefile datafile
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