digsign.java

一个简单的RSA 实现程序

package SimpleRSA;

import java.math.BigInteger;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class DigSign
{
	int[] Load_key(String args)
	{
		String keyfile = Input_Output.Input_Key(args);
		int[] key = new int[2];
		int i;
		i = keyfile.indexOf('p');
		key[0] = Integer.parseInt(keyfile.substring(9, i-2));
		i = keyfile.lastIndexOf(':');
		key[1] = Integer.parseInt(keyfile.substring(i+2,keyfile.length()));
		return key;	
	}
	
	void Sign(String args1,String args2,String args3) throws NoSuchAlgorithmException
	{
		//input plaintext & generate MD
		byte plain[] = Input_Output.Input_PlainForSign(args1);
		String digest = "";
		MessageDigest md = MessageDigest.getInstance("MD5");
		md.update(plain);
		plain= md.digest();
		for(int i=0;i<plain.length;i++)
			{
			 	digest += Integer.toHexString((int)plain[i]+128).toUpperCase();
			}
		System.out.println("The message digest is: " + digest);
		
		//load keys
		int key[] = new int[2];
		key = Load_key(args3);
		
		//sign MD
		BigInteger subplain[] = new BigInteger[plain.length];
		String digest_enc = "";
		for (int i=0;i<subplain.length;i++)
			{
				subplain[i] = BigInteger.valueOf(plain[i]+128);
				subplain[i] = subplain[i].pow(key[1]);
				subplain[i] = subplain[i].mod(BigInteger.valueOf(key[0]));
				if(subplain[i].intValue()>99)
					digest_enc += subplain[i];
				else if(subplain[i].intValue()>9)
					digest_enc = digest_enc + "0" + subplain[i];
				else
					digest_enc = digest_enc + "00" + subplain[i];
			}
		//generate signature
		Input_Output.Output_Cipher(args2, digest_enc);
	}
	
	void Verify(String args1,String args2,String args3) throws NoSuchAlgorithmException
	{
		//input file to generate MD for verify of args1
		byte plain[] = Input_Output.Input_PlainForSign(args1);
		String digest = "";
		MessageDigest md = MessageDigest.getInstance("MD5");
		md.update(plain);
		plain= md.digest();
		for(int i=0;i<plain.length;i++)
			{
			 	digest += Integer.toHexString((int)plain[i]+128).toUpperCase();
			}
		
		//Load keys
		int key[] = new int[2];
		key = Load_key(args3);
		
		//input and decrypt signature of args2
		String digest_dec = "";
		String s = Input_Output.Input_Key(args2);
		int sign[] = new int[s.length()/3];
		for(int i=0;i<sign.length;i++)
			{
				sign[i] = Integer.parseInt(s.substring(i*3,(i+1)*3));
			}
		BigInteger subsign[] = new BigInteger[sign.length];
		for (int i=0;i<subsign.length;i++)
			{
				subsign[i] = BigInteger.valueOf(sign[i]);
				subsign[i] = subsign[i].pow(key[1]);
				subsign[i] = subsign[i].mod(BigInteger.valueOf(key[0]));
				sign[i] = (subsign[i].intValue());
				digest_dec += Integer.toHexString((int)sign[i]).toUpperCase();
			}
		//verify and dispaly result
		System.out.println(digest_dec);
		
		if(digest.equalsIgnoreCase(digest_dec))
			System.out.println("The file has not been modified.");
		else
			System.out.println("The file has been MODIFIED!!!");
	}
}