RSA

RSA.java

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+// Java Program to Implement the RSA Algorithm
+import java.math.*;
+import java.util.*;
+
+class RSA {
+
+  public static void main(String args[]) {
+    Scanner sc = new Scanner(System.in);
+    int p, q, n, z, d = 0, e, i;
+    System.out.println("Enter the number to be encrypted and decrypted");
+    int msg = sc.nextInt();
+
+    double c;
+    BigInteger msgback;
+    System.out.println("Enter 1st prime number p");
+    p = sc.nextInt();
+    System.out.println("Enter 2nd prime number q");
+    q = sc.nextInt();
+
+    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);
+  }
+}