java消息签名

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;

public class SinatureTest {

private static final int KEYSIZE=512;
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
    
try
{
if(args[0].equals("-genkey"))
{
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.println("not ");
}
System.out.println("verifid");
}
}catch(Exception e)
{
e.printStackTrace();
}
}

}


消息签名
1）javac *.java
2)java SignatureTest -genkey public.key private.key
3)java SignatureTest -sign sample.txt.signed private.key
4)java SignatureTest -verify sample.txt.signed public.key