Mega Code Archive
This program demonstrates how to sign a message with a private DSA key and verify it with the matching public key
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/*
This program is a part of the companion code for Core Java 8th ed.
(http://horstmann.com/corejava)
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.SecureRandom;
import java.security.Signature;
/**
* This program demonstrates how to sign a message with a private DSA key and verify it with the
* matching public key. Usage:<br>
* java SignatureTest -genkeypair public private<br>
* java SignatureTest -sign message signed private<br>
* java SignatureTest -verify signed public<br>
* @version 1.11 2007-10-06
* @author Cay Horstmann
*/
public class SignatureTest
{
public static void main(String[] args)
{
try
{
if (args[0].equals("-genkeypair"))
{
KeyPairGenerator pairgen = KeyPairGenerator.getInstance("DSA");
SecureRandom random = new SecureRandom();
pairgen.initialize(KEYSIZE, random);
KeyPair keyPair = pairgen.generateKeyPair();
ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream(args[1]));
out.writeObject(keyPair.getPublic());
out.close();
out = new ObjectOutputStream(new FileOutputStream(args[2]));
out.writeObject(keyPair.getPrivate());
out.close();
}
else if (args[0].equals("-sign"))
{
ObjectInputStream keyIn = new ObjectInputStream(new FileInputStream(args[3]));
PrivateKey privkey = (PrivateKey) keyIn.readObject();
keyIn.close();
Signature signalg = Signature.getInstance("DSA");
signalg.initSign(privkey);
File infile = new File(args[1]);
InputStream in = new FileInputStream(infile);
int length = (int) infile.length();
byte[] message = new byte[length];
in.read(message, 0, length);
in.close();
signalg.update(message);
byte[] signature = signalg.sign();
DataOutputStream out = new DataOutputStream(new FileOutputStream(args[2]));
int signlength = signature.length;
out.writeInt(signlength);
out.write(signature, 0, signlength);
out.write(message, 0, length);
out.close();
}
else if (args[0].equals("-verify"))
{
ObjectInputStream keyIn = new ObjectInputStream(new FileInputStream(args[2]));
PublicKey pubkey = (PublicKey) keyIn.readObject();
keyIn.close();
Signature verifyalg = Signature.getInstance("DSA");
verifyalg.initVerify(pubkey);
File infile = new File(args[1]);
DataInputStream in = new DataInputStream(new FileInputStream(infile));
int signlength = in.readInt();
byte[] signature = new byte[signlength];
in.read(signature, 0, signlength);
int length = (int) infile.length() - signlength - 4;
byte[] message = new byte[length];
in.read(message, 0, length);
in.close();
verifyalg.update(message);
if (!verifyalg.verify(signature)) System.out.print("not ");
System.out.println("verified");
}
}
catch (Exception e)
{
e.printStackTrace();
}
}
private static final int KEYSIZE = 512;
}
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