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RSA encryption #261

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Merged
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Oct 25, 2017
Merged

RSA encryption #261

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62 changes: 62 additions & 0 deletions ciphers/RSA.java
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package ciphers;

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

/**
* Created by Nguyen Duy Tiep on 23-Oct-17.
*/
public class RSA {
private BigInteger modulus, privateKey, publicKey;

public RSA(int bits) {
generateKeys(bits);
}

public synchronized String encrypt(String message) {
return (new BigInteger(message.getBytes())).modPow(publicKey, modulus).toString();
}

public synchronized BigInteger encrypt(BigInteger message) {
return message.modPow(publicKey, modulus);
}

public synchronized String decrypt(String message) {
return new String((new BigInteger(message)).modPow(privateKey, modulus).toByteArray());
}

public synchronized BigInteger decrypt(BigInteger message) {
return message.modPow(privateKey, modulus);
}

/** Generate a new public and private key set. */
public synchronized void generateKeys(int bits) {
SecureRandom r = new SecureRandom();
BigInteger p = new BigInteger(bits / 2, 100, r);
BigInteger q = new BigInteger(bits / 2, 100, r);
modulus = p.multiply(q);

BigInteger m = (p.subtract(BigInteger.ONE)).multiply(q.subtract(BigInteger.ONE));

publicKey = new BigInteger("3");

while (m.gcd(publicKey).intValue() > 1) {
publicKey = publicKey.add(new BigInteger("2"));
}

privateKey = publicKey.modInverse(m);
}

/** Trivial test program. */
public static void main(String[] args) {
RSA rsa = new RSA(1024);

String text1 = "This is a message";
System.out.println("Plaintext: " + text1);

String ciphertext = rsa.encrypt(text1);
System.out.println("Ciphertext: " + ciphertext);

System.out.println("Plaintext: " + rsa.decrypt(ciphertext));
}
}