Added Rsa class

src/main/java/models/Rsa.java

@@ -0,0 +1,56 @@
+package models;
+
+import java.math.BigInteger;
+import java.nio.charset.StandardCharsets;
+import java.security.SecureRandom;
+
+public class Rsa {
+    private final BigInteger e, d, n;
+
+    public Rsa(int numberOfBytes) {
+        BigInteger p = generatePrime(numberOfBytes);
+        BigInteger q = generatePrime(numberOfBytes);
+
+        n = p.multiply(q);
+        BigInteger m = p.subtract(BigInteger.ONE).multiply(q.subtract(BigInteger.ONE));
+
+        e = BigInteger.valueOf(65537); // 2^16 + 1
+        d = e.modInverse(m);
+    }
+
+    private static BigInteger generatePrime(int numberOfBytes) {
+        SecureRandom secureRandom = new SecureRandom();
+        return new BigInteger(numberOfBytes, 100, secureRandom).nextProbablePrime();
+    }
+
+    public BigInteger encrypt(String message) {
+        BigInteger plaintext = toHex(message);
+        return plaintext.modPow(e, n);
+    }
+
+    public String decrypt(BigInteger ciphertext) {
+        BigInteger plaintext = ciphertext.modPow(d, n);
+        return fromHex(plaintext);
+    }
+
+    private static BigInteger toHex(String arg) {
+        return new BigInteger(1, arg.getBytes(StandardCharsets.UTF_8));
+    }
+
+    private static String fromHex(BigInteger arg) {
+        byte[] byteArray = arg.toByteArray();
+        return new String(byteArray, StandardCharsets.UTF_8);
+    }
+
+    public BigInteger getE() {
+        return e;
+    }
+
+    public BigInteger getD() {
+        return d;
+    }
+
+    public BigInteger getN() {
+        return n;
+    }
+}