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| import java.math.BigInteger;
import java.util.Random;
import java.lang.StringBuffer;
import java.util.Scanner;
/**
* rsa
*/
public class rsa {
public static void main(String[] args) {
Calculate c = new Calculate();
Scanner sc = new Scanner(System.in);
BigInteger p = (new Prime()).getPrime(1024);
BigInteger q = (new Prime()).getPrime(1024);
BigInteger e = new BigInteger("65537");
BigInteger n = p.multiply(q); // n = p * q
BigInteger r = c.euler(p, q); // (p-1)(q-1)
BigInteger d = c.modInverse(e, r);
while (true) {
if (c.gcd(e, r).equals(BigInteger.ONE)) {
break;
} else {
e = e.subtract(BigInteger.ONE);
}
}
System.out.println("p: " + p);
System.out.println("q: " + q);
System.out.println("d: " + d);
System.out.println("n: " + n);
System.out.println("e: " + e);
System.out.print("Input message: ");
BigInteger M = new BigInteger(sc.next());
BigInteger C = c.powmod(M, e, n);
System.out.println("Ciphertext: " + C);
BigInteger M2 = c.powmod(C, d, n);
System.out.println("Decrypted message: " + M2);
sc.close();
}
}
class Calculate {
public BigInteger powmod(BigInteger p, BigInteger q, BigInteger n) {
BigInteger result = new BigInteger("1");
while (q.compareTo(BigInteger.ZERO) == 1) {
if (q.testBit(0)) {
result = result.multiply(p).mod(n);
}
q = q.shiftRight(1);
p = p.multiply(p).mod(n);
}
return result;
}
public BigInteger euler(BigInteger p, BigInteger q) {
return p.subtract(BigInteger.ONE).multiply(q.subtract(BigInteger.ONE));
}
public BigInteger gcd(BigInteger a, BigInteger b) {
while (a.compareTo(BigInteger.ZERO) != 0) {
BigInteger t = a;
a = b.mod(a);
b = t;
}
return b;
}
public BigInteger modInverse(BigInteger a, BigInteger b) {
// y1 = e^-1 mod r
BigInteger x0 = a, x1 = BigInteger.ZERO,
y0 = b, y1 = BigInteger.ONE;
while (y0.compareTo(BigInteger.ZERO) != 0) {
BigInteger t1 = x1;
x1 = y1.subtract(x0.divide(y0).multiply(x1));
y1 = t1;
BigInteger t0 = x0;
x0 = y0;
y0 = t0.mod(y0);
}
if (y1.compareTo(BigInteger.ZERO) == -1) {
y1 = y1.add(b);
}
return y1;
}
}
class Prime {
Calculate c = new Calculate();
public BigInteger fakePrime(int bits) {
Random r = new Random();
StringBuffer sb=new StringBuffer();
sb.append("1");
for (int i = 0; i < bits - 2; i++) {
sb.append(r.nextInt(2));
}
sb.append("1");
return new BigInteger(sb.toString(), 2);
}
public boolean prime_miller_rabin(BigInteger n, BigInteger k) {
BigInteger one = BigInteger.ONE;
BigInteger two = BigInteger.TWO;
String[] primes = {"2", "3", "5", "7", "11", "13", "17", "19", "23", "29", "31",
"37", "41", "43", "47", "53", "59", "61", "67", "71", "73",
"79","83","89","97"};
for (String prime : primes) {
if (n.divideAndRemainder(new BigInteger(prime))[1].equals(BigInteger.ZERO)) {
return false;
}
}
if (c.powmod(k, n.subtract(one), n).equals(one)) {
BigInteger d = n.subtract(one);
int q = 0;
while (!d.testBit(0)) {
q++;
d = d.shiftRight(1);
}
BigInteger m = d;
for (int i = 0; i < q; i++) {
BigInteger u = m.multiply(two.pow(i));
BigInteger tmp = c.powmod(k, u, n);
if (tmp.equals(one) || tmp.equals(n.subtract(one))) {
return true;
}
}
return false;
} else {
return false;
}
}
public BigInteger getPrime(int bit) {
BigInteger prime_number = fakePrime(bit);
BigInteger rand = fakePrime(50);
while (true) {
boolean flag = false;
for (int i = 0; i < 5; i++) {
if (!this.prime_miller_rabin(prime_number, rand)) {
flag = true;
}
}
if (flag) {
prime_number = fakePrime(bit);
} else {
return prime_number;
}
}
}
}
|