Change project structure to a Maven Java project + Refactor (#2816)

src/main/java/com/thealgorithms/ciphers/RSA.java

@@ -0,0 +1,76 @@
+package com.thealgorithms.ciphers;
+
+import javax.swing.*;
+import java.math.BigInteger;
+import java.security.SecureRandom;
+
+/**
+ * @author Nguyen Duy Tiep on 23-Oct-17.
+ */
+public final class RSA {
+
+    public static void main(String[] args) {
+
+        RSA rsa = new RSA(1024);
+        String text1 = JOptionPane.showInputDialog("Enter a message to encrypt :");
+
+        String ciphertext = rsa.encrypt(text1);
+        JOptionPane.showMessageDialog(null, "Your encrypted message : " + ciphertext);
+
+        JOptionPane.showMessageDialog(null, "Your message after decrypt : " + rsa.decrypt(ciphertext));
+    }
+
+    private BigInteger modulus, privateKey, publicKey;
+
+    public RSA(int bits) {
+        generateKeys(bits);
+    }
+
+    /**
+     * @return encrypted message
+     */
+    public synchronized String encrypt(String message) {
+        return (new BigInteger(message.getBytes())).modPow(publicKey, modulus).toString();
+    }
+
+    /**
+     * @return encrypted message as big integer
+     */
+    public synchronized BigInteger encrypt(BigInteger message) {
+        return message.modPow(publicKey, modulus);
+    }
+
+    /**
+     * @return plain message
+     */
+    public synchronized String decrypt(String encryptedMessage) {
+        return new String((new BigInteger(encryptedMessage)).modPow(privateKey, modulus).toByteArray());
+    }
+
+    /**
+     * @return plain message as big integer
+     */
+    public synchronized BigInteger decrypt(BigInteger encryptedMessage) {
+        return encryptedMessage.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);
+    }
+}