RSA Algorithm in JAVA

BasicRSA.java

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+
+import java.math.BigInteger;
+import java.util.Scanner;
+
+public class BasicRSA{
+
+    static int gcd(int a, int b)
+    {   /*Returns Greatest common divisor of 2 numbers
+         *implementing Euclidean ALgorithm */
+
+        if (a == 0) return b;
+        else return gcd(b % a, a);
+    }
+
+    static int modInv(int a, int b)
+    {   /*Returns modular inverse of a mod b
+        *implementing Extended Euclidean ALgorithm*/
+        return modInv(a,b,b,0,1);
+    }
+
+    static int modInv(int a,int b,int c,int x,int y)
+    {   //over-loading
+
+         if(b%a==0) return y;
+         else return modInv(b%a,a,c,y,c+(x-(b/a)*y)%c ); 
+    }
+
+    public static void main(String args[]){
+
+        Scanner sc= new Scanner(System.in);
+        System.out.println("You are required to enter 2 prime numbers followed by the message you want to encrypt");
+
+        System.out.println("Enter first prime :");
+        int p= sc.nextInt();
+
+        System.out.println("Enter Second prime:");
+        int q=sc.nextInt();
+
+        System.out.println("Enter a num to encrypt:");
+        int m=sc.nextInt(); 
+        //Plaintext: message to be encrypted
+
+        sc.close();
+
+        int n=p*q;
+        int z=(p-1)*(q-1)/gcd(p-1,q-1);
+        int e,d=0; // e is for public key exponent, d is for private key exponent
+
+        for (e = 2; e < z; e++) {
+            if (gcd(e, z) == 1) {
+                break;
+            }
+        }
+
+        d=modInv(e,z);
+
+        BigInteger M= BigInteger.valueOf(m);
+        BigInteger E= BigInteger.valueOf(e);
+        BigInteger N= BigInteger.valueOf(n);
+        BigInteger D= BigInteger.valueOf(d);
+        BigInteger C= M.modPow(E,N);
+        BigInteger M2= C.modPow(D,N);
+
+
+
+        System.out.println("Public Key Pair : " + e + " " + n );
+        System.out.println("Private Key Pair : " + d + " " + n );
+        System.out.println("Encrypted num : "+ C);                 
+        System.out.println("Decrypted num : "+ M2);
+        System.out.println("This is deciphered using Private key");
+    }
+}