Cryptography in Java: Encryption and Hashing — Complete Guide

Cryptography in Java: Encryption and Hashing — Detailed Guide

In the modern world of information security, cryptography is the foundation of data protection. Java provides a powerful built-in toolkit for implementing encryption and hashing through the javax.crypto and java.security packages. In this article, we will thoroughly examine the main cryptographic operations in Java: symmetric and asymmetric encryption, password hashing, and working with digital signatures.

1. Fundamentals of Cryptography in Java

Java Cryptography Architecture (JCA) is a framework that allows developers to easily integrate cryptographic algorithms. Key classes:

• javax.crypto.Cipher — for encryption and decryption.
• java.security.MessageDigest — for hashing.
• java.security.KeyPairGenerator — for key generation.
• javax.crypto.spec.SecretKeySpec — for creating symmetric keys.

To work with cryptography, import:

import javax.crypto.*;import javax.crypto.spec.*;import java.security.*;

2. Symmetric Encryption (AES)

Symmetric encryption uses a single key for both encryption and decryption. AES (Advanced Encryption Standard) is the most popular algorithm. Example of encrypting a string:

import javax.crypto.*;import javax.crypto.spec.*;import java.util.Base64;

public class AesExample {    public static void main(String[] args) throws Exception {        String plainText = "Secret message";        String secretKey = "0123456789abcdef"; // 16 bytes for AES-128

        // Creating the key        SecretKeySpec keySpec = new SecretKeySpec(secretKey.getBytes(), "AES");        Cipher cipher = Cipher.getInstance("AES/ECB/PKCS5Padding");

        // Encryption        cipher.init(Cipher.ENCRYPT_MODE, keySpec);        byte[] encryptedBytes = cipher.doFinal(plainText.getBytes());        String encryptedText = Base64.getEncoder().encodeToString(encryptedBytes);        System.out.println("Encrypted: " + encryptedText);

        // Decryption        cipher.init(Cipher.DECRYPT_MODE, keySpec);        byte[] decryptedBytes = cipher.doFinal(Base64.getDecoder().decode(encryptedText));        String decryptedText = new String(decryptedBytes);        System.out.println("Decrypted: " + decryptedText);    }}

Important: The ECB mode is not recommended for large amounts of data. Use AES/GCM/NoPadding for better security.

3. Asymmetric Encryption (RSA)

Asymmetric encryption uses a pair of keys: a public key (for encryption) and a private key (for decryption). RSA is a classic algorithm. Example:

import javax.crypto.*;import java.security.*;import java.util.Base64;

public class RsaExample {    public static void main(String[] args) throws Exception {        // Generating a key pair        KeyPairGenerator keyGen = KeyPairGenerator.getInstance("RSA");        keyGen.initialize(2048);        KeyPair pair = keyGen.generateKeyPair();        PublicKey publicKey = pair.getPublic();        PrivateKey privateKey = pair.getPrivate();

        // Encryption with the public key        Cipher cipher = Cipher.getInstance("RSA/ECB/OAEPWithSHA-256AndMGF1Padding");        cipher.init(Cipher.ENCRYPT_MODE, publicKey);        byte[] encryptedBytes = cipher.doFinal("Secret data".getBytes());        String encryptedText = Base64.getEncoder().encodeToString(encryptedBytes);        System.out.println("Encrypted with RSA: " + encryptedText);

        // Decryption with the private key        cipher.init(Cipher.DECRYPT_MODE, privateKey);        byte[] decryptedBytes = cipher.doFinal(Base64.getDecoder().decode(encryptedText));