[RSA] Encryption and Decryption Code [Java]

[drudown500]

// Java Program to Implement the RSA Algorithm
import java.math.*;
import java.util.*;

class RSA {
public static void main(String args[])
{
int p, q, n, z, d = 0, e, i;

// The number to be encrypted and decrypted
int msg = 12;
double c;
BigInteger msgback;

// 1st prime number p
p = 3;

// 2nd prime number q
q = 11;
n = p * q;
z = (p - 1) * (q - 1);
System.out.println("the value of z = " + z);

for (e = 2; e < z; e++) {

// e is for public key exponent
if (gcd(e, z) == 1) {
break;
}
}
System.out.println("the value of e = " + e);
for (i = 0; i <= 9; i++) {
int x = 1 + (i * z);

// d is for private key exponent
if (x % e == 0) {
d = x / e;
break;
}
}
System.out.println("the value of d = " + d);
c = (Math.pow(msg, e)) % n;
System.out.println("Encrypted message is : " + c);

// converting int value of n to BigInteger
BigInteger N = BigInteger.valueOf(n);

// converting float value of c to BigInteger
BigInteger C = BigDecimal.valueOf(c).toBigInteger();
msgback = (C.pow(d)).mod(N);
System.out.println("Decrypted message is : "
+ msgback);
}

static int gcd(int e, int z)
{
if (e == 0)
return z;
else
return gcd(z % e, e);
}
}

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