signdata.java

java编写的一个对文件的数字签名,是对内容进行签名适合于小文件..特别是一些密码文件

import java.io.*;
import java.security.*;
import java.security.spec.*;
public class SignData{
	public static void main(String [] args)
	{
		FileOutputStream fileOut;
		byte b;
		if(args.length!=3)
		{
		System.out.println("Usage:SignData <PrivateKey> <dataFile> <SignatureFile>");
		System.out.println("Option:");
		System.out.println("<PrivateKey>:The file name of the private Key.");
		System.out.println("<DataFile>: The filename that want to signature.");
		System.out.println("<signatureFile>:the filename containing signture data.");
		}
	try{
		System.out.println("Generating a digital signature....");
		FileInputStream fileIn=new FileInputStream(args[0]);
		byte[] encodedprivateKey=new byte[fileIn.available()];

		fileIn.read(encodedprivateKey);
		fileIn.close();

		PKCS8EncodedKeySpec privKeySpec=	new PKCS8EncodedKeySpec(encodedprivateKey);
		KeyFactory keyFactory=KeyFactory.getInstance("DSA");
		PrivateKey privKey=keyFactory.generatePrivate(privKeySpec);
		Signature dsa=Signature.getInstance("SHA/DSA");
		dsa.initSign(privKey);
		FileInputStream fis=new FileInputStream(args[1]);
		while(fis.available()!=0)
		{
		b=(byte)fis.read();
		dsa.update(b);
		}
		fis.close();
		byte[] sig=dsa.sign();
		fileOut=new FileOutputStream(args[2]);
		fileOut.write(sig);
		fileOut.close();
		System.out.println("OK");
	}
	catch(Exception e)
	{
	}
 }
}