import java.math.BigInteger;
import java.security.SecureRandom;

class Rsa {
  
  private BigInteger r, v, e;

  public Rsa(int bitlen) {
    SecureRandom rand = new SecureRandom();
    // Erzeugen großer Primzahlen mit bitlen Bit-Stellen
    BigInteger p = new BigInteger(bitlen / 2, 100, rand);
    BigInteger q = new BigInteger(bitlen / 2, 100, rand);
    r = p.multiply(q);
    BigInteger m = (p.subtract(BigInteger.ONE)).multiply(q
        .subtract(BigInteger.ONE));
    // berechne v, relativ prim zu (p-1)(q-1)
    v = new BigInteger("3");
    while (m.gcd(v).intValue() > 1)
      v = v.add(new BigInteger("2"));
    // berechne e, das multiplikativ Inverse zu v (mod (p-1)(q-1)) 
    e = v.modInverse(m);
  }

  public BigInteger encrypt(BigInteger message) {
    return message.modPow(v, r);
  }

  public BigInteger decrypt(BigInteger message) {
    return message.modPow(e, r);
  }

    public static void main(String[] args) {
	Rsa rsa = new Rsa(128);
	if (args.length != 1) {
	    System.out.println("Usage: java Rsa <value>");
	    System.exit(1);
	}
	BigInteger value = new BigInteger(args[0]);
	System.out.println("Original value: " + value);
	BigInteger encryptedValue = rsa.encrypt(value);
	System.out.println("Encrypted value: " + encryptedValue);
	BigInteger decryptedValue = rsa.decrypt(encryptedValue);
	System.out.println("Decrypted Value: " + decryptedValue);
    }

}