Condensed RSA

Condensed-RSA Definition:

package sig;import java.security.*;import java.security.interfaces.RSAPublicKey;import java.security.interfaces.RSAPrivateKey;import javax.crypto.Cipher;import Tool.Hasher;import java.math.BigInteger;import java.security.MessageDigest;import java.util.*;public class signature {    public static int byteArrayToInt(byte[] b) {          return   b[3] & 0xFF |                  (b[2] & 0xFF) << 8 |                  (b[1] & 0xFF) << 16 |                  (b[0] & 0xFF) << 24;      }    //change a string to integer using sha1 algorithm    public static int digest(String s) {        int result = 0;        try {            MessageDigest messageDigest =MessageDigest.getInstance("SHA-1");            byte[] inputByteArray = s.getBytes("utf-8");            messageDigest.update(inputByteArray);            byte[] resultbyte = messageDigest.digest();            result = byteArrayToInt(resultbyte);        }catch(Exception e) {}        return result;    }    public static void main(String[] args)throws Exception{        KeyPairGenerator gen = KeyPairGenerator.getInstance("RSA");        gen.initialize(512);        KeyPair keyPair = gen.generateKeyPair();        PublicKey publickey = keyPair.getPublic();        PrivateKey privatekey = keyPair.getPrivate();        RSAPublicKey rsaPublicKey = (RSAPublicKey) publickey;        RSAPrivateKey rsaPrivateKey = (RSAPrivateKey) privatekey;        BigInteger n = rsaPublicKey.getModulus();        BigInteger e = rsaPublicKey.getPublicExponent();        BigInteger d = rsaPrivateKey.getPrivateExponent();        BigInteger num1 = new BigInteger("3");        BigInteger mul = num1.modPow(e, n).modPow(d, n);        System.out.println(mul);        String str1 = new String("2ef7bde608ce5404e97d5f042f95f89f1c232871");        int hashnum1 = digest(str1);        String str2 = new String("361772a491529e2ddc1740c7a8187bf466faeb41");        int hashnum2 = digest(str1);        BigInteger bighashnum1 = new BigInteger(""+hashnum1);        BigInteger bighashnum2 = new BigInteger(""+hashnum2);        long start = System.nanoTime();        BigInteger mulmod = bighashnum1.multiply(bighashnum2).mod(n);        BigInteger sig1 = bighashnum1.modPow(e,n);        BigInteger sig2 = bighashnum2.modPow(e, n);        BigInteger sigmul = sig1.multiply(sig2).mod(n);        BigInteger decryptedsigmul = sigmul.modPow(d, n);        long end = System.nanoTime();        System.out.println(decryptedsigmul.equals(mulmod));        System.out.println((end-start));    }}