8.2 Cryptography Explained

Cryptography is the practice of securing information by transforming it into a format that is unreadable to unauthorized parties. In Java SE 11, cryptography is implemented through the Java Cryptography Architecture (JCA) and the Java Cryptography Extension (JCE). Understanding cryptography is essential for creating secure applications that protect sensitive data.

Key Concepts

1. Encryption and Decryption

Encryption is the process of converting plaintext into ciphertext using an algorithm and a key. Decryption is the reverse process, converting ciphertext back into plaintext using the same or a corresponding key.

Example

        Cipher cipher = Cipher.getInstance("AES");
        SecretKey secretKey = new SecretKeySpec(key, "AES");
        cipher.init(Cipher.ENCRYPT_MODE, secretKey);
        byte[] encryptedBytes = cipher.doFinal(plaintext.getBytes());
    

2. Symmetric Encryption

Symmetric encryption uses the same key for both encryption and decryption. Common symmetric encryption algorithms include AES (Advanced Encryption Standard) and DES (Data Encryption Standard).

Example

        KeyGenerator keyGen = KeyGenerator.getInstance("AES");
        keyGen.init(128);
        SecretKey secretKey = keyGen.generateKey();
    

3. Asymmetric Encryption

Asymmetric encryption uses a pair of keys: a public key for encryption and a private key for decryption. Common asymmetric encryption algorithms include RSA (Rivest-Shamir-Adleman) and ECC (Elliptic Curve Cryptography).

Example

        KeyPairGenerator keyGen = KeyPairGenerator.getInstance("RSA");
        keyGen.initialize(2048);
        KeyPair keyPair = keyGen.generateKeyPair();
    

4. Digital Signatures

Digital signatures are used to verify the authenticity and integrity of data. They use asymmetric encryption to create a signature that can be verified using the sender's public key.

Example

        Signature signature = Signature.getInstance("SHA256withRSA");
        signature.initSign(privateKey);
        signature.update(data);
        byte[] digitalSignature = signature.sign();
    

5. Hashing

Hashing is the process of converting data into a fixed-size string of bytes using a hash function. Hash functions are one-way and produce a unique hash value for each input. Common hash functions include SHA-256 and MD5.

Example

        MessageDigest digest = MessageDigest.getInstance("SHA-256");
        byte[] hash = digest.digest(data.getBytes());
    

6. Key Management

Key management involves the generation, storage, and distribution of cryptographic keys. Proper key management is crucial for maintaining the security of encrypted data.

Example

        KeyStore keyStore = KeyStore.getInstance("JKS");
        keyStore.load(new FileInputStream("keystore.jks"), "password".toCharArray());
    

Examples and Analogies

Think of cryptography as a secure vault for your data. Encryption is like locking the vault with a key, ensuring that only those with the key can access the contents. Symmetric encryption is like a single key that opens and locks the vault, while asymmetric encryption is like a pair of keys: one for locking (public key) and one for unlocking (private key). Digital signatures are like a seal on a document, proving its authenticity and integrity. Hashing is like a fingerprint for data, uniquely identifying it without revealing its contents. Key management is like keeping the keys to the vault safe and secure, ensuring that only authorized individuals can access them.

By mastering cryptography, you can create secure Java SE 11 applications that protect sensitive data from unauthorized access and ensure the integrity and authenticity of information.