diff --git a/src/main/java/com/thealgorithms/ciphers/RSA.java b/src/main/java/com/thealgorithms/ciphers/RSA.java
index f50e501e68c8..28af1a62032a 100644
--- a/src/main/java/com/thealgorithms/ciphers/RSA.java
+++ b/src/main/java/com/thealgorithms/ciphers/RSA.java
@@ -4,7 +4,27 @@
import java.security.SecureRandom;
/**
- * @author Nguyen Duy Tiep on 23-Oct-17.
+ * RSA is an asymmetric cryptographic algorithm used for secure data encryption and decryption.
+ * It relies on a pair of keys: a public key (used for encryption) and a private key
+ * (used for decryption). The algorithm is based on the difficulty of factoring large prime numbers.
+ *
+ * This implementation includes key generation, encryption, and decryption methods that can handle both
+ * text-based messages and BigInteger inputs. For more details on RSA:
+ * RSA Cryptosystem - Wikipedia.
+ *
+ * Example Usage:
+ *
+ * RSA rsa = new RSA(1024);
+ * String encryptedMessage = rsa.encrypt("Hello RSA!");
+ * String decryptedMessage = rsa.decrypt(encryptedMessage);
+ * System.out.println(decryptedMessage); // Output: Hello RSA!
+ *
+ *
+ * Note: The key size directly affects the security and performance of the RSA algorithm.
+ * Larger keys are more secure but slower to compute.
+ *
+ * @author Nguyen Duy Tiep
+ * @version 23-Oct-17
*/
public class RSA {
@@ -12,55 +32,88 @@ public class RSA {
private BigInteger privateKey;
private BigInteger publicKey;
+ /**
+ * Constructor that generates RSA keys with the specified number of bits.
+ *
+ * @param bits The bit length of the keys to be generated. Common sizes include 512, 1024, 2048, etc.
+ */
public RSA(int bits) {
generateKeys(bits);
}
/**
- * @return encrypted message
+ * Encrypts a text message using the RSA public key.
+ *
+ * @param message The plaintext message to be encrypted.
+ * @throws IllegalArgumentException If the message is empty.
+ * @return The encrypted message represented as a String.
*/
public synchronized String encrypt(String message) {
+ if (message.isEmpty()) {
+ throw new IllegalArgumentException("Message is empty");
+ }
return (new BigInteger(message.getBytes())).modPow(publicKey, modulus).toString();
}
/**
- * @return encrypted message as big integer
+ * Encrypts a BigInteger message using the RSA public key.
+ *
+ * @param message The plaintext message as a BigInteger.
+ * @return The encrypted message as a BigInteger.
*/
public synchronized BigInteger encrypt(BigInteger message) {
return message.modPow(publicKey, modulus);
}
/**
- * @return plain message
+ * Decrypts an encrypted message (as String) using the RSA private key.
+ *
+ * @param encryptedMessage The encrypted message to be decrypted, represented as a String.
+ * @throws IllegalArgumentException If the message is empty.
+ * @return The decrypted plaintext message as a String.
*/
public synchronized String decrypt(String encryptedMessage) {
+ if (encryptedMessage.isEmpty()) {
+ throw new IllegalArgumentException("Message is empty");
+ }
return new String((new BigInteger(encryptedMessage)).modPow(privateKey, modulus).toByteArray());
}
/**
- * @return plain message as big integer
+ * Decrypts an encrypted BigInteger message using the RSA private key.
+ *
+ * @param encryptedMessage The encrypted message as a BigInteger.
+ * @return The decrypted plaintext message as a BigInteger.
*/
public synchronized BigInteger decrypt(BigInteger encryptedMessage) {
return encryptedMessage.modPow(privateKey, modulus);
}
/**
- * Generate a new public and private key set.
+ * Generates a new RSA key pair (public and private keys) with the specified bit length.
+ * Steps:
+ * 1. Generate two large prime numbers p and q.
+ * 2. Compute the modulus n = p * q.
+ * 3. Compute Euler's totient function: φ(n) = (p-1) * (q-1).
+ * 4. Choose a public key e (starting from 3) that is coprime with φ(n).
+ * 5. Compute the private key d as the modular inverse of e mod φ(n).
+ * The public key is (e, n) and the private key is (d, n).
+ *
+ * @param bits The bit length of the keys to be generated.
*/
public final 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);
+ SecureRandom random = new SecureRandom();
+ BigInteger p = new BigInteger(bits / 2, 100, random);
+ BigInteger q = new BigInteger(bits / 2, 100, random);
modulus = p.multiply(q);
- BigInteger m = (p.subtract(BigInteger.ONE)).multiply(q.subtract(BigInteger.ONE));
+ BigInteger phi = (p.subtract(BigInteger.ONE)).multiply(q.subtract(BigInteger.ONE));
publicKey = BigInteger.valueOf(3L);
-
- while (m.gcd(publicKey).intValue() > 1) {
+ while (phi.gcd(publicKey).intValue() > 1) {
publicKey = publicKey.add(BigInteger.TWO);
}
- privateKey = publicKey.modInverse(m);
+ privateKey = publicKey.modInverse(phi);
}
}
diff --git a/src/test/java/com/thealgorithms/ciphers/RSATest.java b/src/test/java/com/thealgorithms/ciphers/RSATest.java
index c82f68d11f4c..577f56426be8 100644
--- a/src/test/java/com/thealgorithms/ciphers/RSATest.java
+++ b/src/test/java/com/thealgorithms/ciphers/RSATest.java
@@ -1,23 +1,64 @@
package com.thealgorithms.ciphers;
import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import java.math.BigInteger;
import org.junit.jupiter.api.Test;
class RSATest {
- RSA rsa = new RSA(1024);
+ private final RSA rsa = new RSA(1024);
@Test
- void testRSA() {
- // given
- String textToEncrypt = "Such secure";
+ void testEncryptDecryptString() {
+ String originalMessage = "Such secure";
+ String encryptedMessage = rsa.encrypt(originalMessage);
+ String decryptedMessage = rsa.decrypt(encryptedMessage);
+ assertEquals(originalMessage, decryptedMessage);
+ }
+
+ @Test
+ void testEncryptDecryptBigInteger() {
+ BigInteger originalMessage = new BigInteger("12345678901234567890");
+ BigInteger encryptedMessage = rsa.encrypt(originalMessage);
+ BigInteger decryptedMessage = rsa.decrypt(encryptedMessage);
+ assertEquals(originalMessage, decryptedMessage);
+ }
- // when
- String cipherText = rsa.encrypt(textToEncrypt);
- String decryptedText = rsa.decrypt(cipherText);
+ @Test
+ void testEmptyMessage() {
+ String originalMessage = "";
+ assertThrows(IllegalArgumentException.class, () -> rsa.encrypt(originalMessage));
+ assertThrows(IllegalArgumentException.class, () -> rsa.decrypt(originalMessage));
+ }
+
+ @Test
+ void testDifferentKeySizes() {
+ // Testing with 512-bit RSA keys
+ RSA smallRSA = new RSA(512);
+ String originalMessage = "Test with smaller key";
- // then
- assertEquals("Such secure", decryptedText);
+ String encryptedMessage = smallRSA.encrypt(originalMessage);
+ String decryptedMessage = smallRSA.decrypt(encryptedMessage);
+
+ assertEquals(originalMessage, decryptedMessage);
+
+ // Testing with 2048-bit RSA keys
+ RSA largeRSA = new RSA(2048);
+ String largeOriginalMessage = "Test with larger key";
+
+ String largeEncryptedMessage = largeRSA.encrypt(largeOriginalMessage);
+ String largeDecryptedMessage = largeRSA.decrypt(largeEncryptedMessage);
+
+ assertEquals(largeOriginalMessage, largeDecryptedMessage);
+ }
+
+ @Test
+ void testSpecialCharacters() {
+ String originalMessage = "Hello, RSA! @2024#";
+ String encryptedMessage = rsa.encrypt(originalMessage);
+ String decryptedMessage = rsa.decrypt(encryptedMessage);
+ assertEquals(originalMessage, decryptedMessage);
}
}