Write a program to implement Digital Signature Algorithm. Information and Network Security (2170709) GTU

Algorithm/Steps:

              For the signing process, A signs a message m by the following procedure:

1. Select a random, secret integer k, such that 0 < k < q − 1.

2. Compute r = (α^k(mod p)) (mod q)

3. Compute s = (k^(−1)(m + ar)) (mod q)

4. A sends the signature (m, r, s) for m to B.

For the verification process, B verifies the signature by the following procedure:

1. B can use A’s public information (p, q, α, β) = (23929, 997, 20424, 1483).

2. Compute u1 ≡ s^(−1) m (mod q), and u2 ≡ s−1 r (mod q). 3. Compute v = (α^u1*β^u2(mod p)) (mod q) 4. B accepts the signature iff v = r. Steps: 1. select public keys (p, q, α, β) 2. sign a message m (0 < m < q − 1) with a random k and report (m, r, s).

3. verifies (m, r, s) for m based on the public key (p, q, α, β).

Code:

import java.math.*;

import java.util.*;

import java.security.*;

import java.io.*;

public class dsa

{

 public static void main(String[] args) throws IOException

{

Scanner sca = new Scanner(System.in);

BigInteger p, b, c, secretKey;

 Random sc = new SecureRandom();

 secretKey = new BigInteger("12345678901234567890");

 System.out.println("secretKey = " + secretKey);

p = BigInteger.probablePrime(64, sc);

b = new BigInteger("3");

c = b.modPow(secretKey, p);

System.out.println("p = " + p);

System.out.println("b = " + b);

System.out.println("c = " + c);

System.out.print("Enter your Big Number message -->");

String s = sca.nextLine();

BigInteger X = new BigInteger(s);

BigInteger r = new BigInteger(64, sc);

BigInteger EC = X.multiply(c.modPow(r, p)).mod(p);

BigInteger brmodp = b.modPow(r, p);

System.out.println("Plaintext = " + X);

System.out.println("r = " + r);

System.out.println("EC = " + EC);

System.out.println("b^r mod p = " + brmodp);

BigInteger crmodp = brmodp.modPow(secretKey, p);

BigInteger d = crmodp.modInverse(p);

BigInteger ad = d.multiply(EC).mod(p);

System.out.println("\n\nc^r mod p = " + crmodp);

System.out.println("d = " + d);

System.out.println("A decodes: " + ad);

}

}