JCrypter Tutorial: Encrypting and Decrypting Data Step‑by‑Step### Introduction
JCrypter is a hypothetical Java-based encryption library designed to make symmetric and asymmetric cryptography straightforward for developers. This tutorial walks through key concepts, installation, common use cases, and step‑by‑step examples for encrypting and decrypting data securely using JCrypter. We’ll cover symmetric (AES) encryption for bulk data and asymmetric (RSA) encryption for key exchange/signing, plus best practices and common pitfalls.
Table of contents
- Background: encryption basics
- Installation and setup
- Symmetric encryption (AES) — encrypt/decrypt examples
- Asymmetric encryption (RSA) — key generation, encrypt/decrypt, signing
- Hybrid encryption: combining AES and RSA
- Key management and storage best practices
- Performance considerations
- Common mistakes and how to avoid them
- Example project: secure file storage
- Conclusion
1. Background: encryption basics
- Confidentiality — keeping data secret (encryption).
- Integrity — ensuring data hasn’t been altered (MACs, AEAD).
- Authentication — verifying identity (digital signatures).
- Symmetric encryption uses the same secret key for encryption and decryption (fast, suitable for large data).
- Asymmetric encryption uses a public/private key pair (useful for key exchange, signatures; slower).
- AEAD (Authenticated Encryption with Associated Data) modes like AES‑GCM provide confidentiality and integrity together — preferred over plain AES‑CBC+HMAC.
2. Installation and setup
Assume JCrypter is available as a Maven artifact. Add to your pom.xml:
<dependency> <groupId>com.example</groupId> <artifactId>jcrypter</artifactId> <version>1.0.0</version> </dependency> Or Gradle:
implementation 'com.example:jcrypter:1.0.0' Import typical classes in your Java code:
import com.example.jcrypter.JCrypter; import com.example.jcrypter.KeyPair; import com.example.jcrypter.SecretKey; 3. Symmetric encryption (AES) — encrypt/decrypt examples
Best practice: use AES‑GCM with a strong random key and unique IV per message. Example usage:
// Generate a new AES key (256-bit) SecretKey aesKey = JCrypter.generateAesKey(256); // Plaintext byte[] plaintext = "Sensitive data".getBytes(StandardCharsets.UTF_8); // Encrypt with AES-GCM byte[] iv = JCrypter.generateIv(12); // 12 bytes recommended for GCM byte[] ciphertext = JCrypter.encryptAesGcm(aesKey, iv, plaintext, aad /* can be null */); // Store or transmit: iv + ciphertext (and tag included) Decrypt:
byte[] decrypted = JCrypter.decryptAesGcm(aesKey, iv, ciphertext, aad); String recovered = new String(decrypted, StandardCharsets.UTF_8); Notes:
- Never reuse an IV with the same key for GCM.
- Use 96‑bit (12 byte) IVs for AES‑GCM.
- Prefer 256‑bit keys when available.
4. Asymmetric encryption (RSA) — key generation, encrypt/decrypt, signing
Key generation:
KeyPair rsaKeyPair = JCrypter.generateRsaKeyPair(2048); PublicKey pub = rsaKeyPair.getPublic(); PrivateKey priv = rsaKeyPair.getPrivate(); Encrypt with RSA (for small data or keys):
byte[] secret = "short secret".getBytes(UTF_8); byte[] encrypted = JCrypter.encryptRsaOaep(pub, secret); byte[] decrypted = JCrypter.decryptRsaOaep(priv, encrypted); Sign and verify:
byte[] signature = JCrypter.signRsaPss(priv, message); boolean ok = JCrypter.verifyRsaPss(pub, message, signature); Use RSA‑OAEP for encryption and RSA‑PSS for signatures.
5. Hybrid encryption: combining AES and RSA
For large data, encrypt with AES and then encrypt the AES key with the recipient’s RSA public key.
High-level steps:
- Generate AES key and IV.
- Encrypt data with AES‑GCM.
- Encrypt AES key with recipient’s RSA public key using OAEP.
- Send {encryptedKey, iv, ciphertext}.
Example:
SecretKey aesKey = JCrypter.generateAesKey(256); byte[] iv = JCrypter.generateIv(12); byte[] ciphertext = JCrypter.encryptAesGcm(aesKey, iv, plaintext, null); byte[] encryptedKey = JCrypter.encryptRsaOaep(recipientPub, aesKey.getEncoded()); Recipient decrypts AES key with RSA private key, then decrypts ciphertext.
6. Key management and storage best practices
- Use secure keystores (PKCS#12, OS keychain) or HSMs.
- Rotate keys periodically.
- Protect private keys with strong passphrases and limited access.
- Never hard‑code keys in source.
- Log key IDs, not key material.
7. Performance considerations
- Symmetric algorithms (AES) are much faster than RSA. Use AES for bulk encryption.
- Avoid unnecessary serialization of large byte arrays; stream when encrypting files.
- Use native providers (e.g., OpenJDK’s SunJCE or BouncyCastle) for optimized implementations.
8. Common mistakes and how to avoid them
- Reusing IVs with AES‑GCM — always use a unique IV.
- Using ECB mode — insecure, avoid.
- Not authenticating ciphertext — use AEAD or HMAC+encrypt-then-MAC.
- Insecure random number generators — use SecureRandom.
- Storing plaintext or keys in logs.
9. Example project: secure file storage
Outline:
- CLI that encrypts files with AES‑GCM, stores encrypted AES key (RSA‑OAEP) per user.
- Commands: generate-keys, encrypt-file, decrypt-file, rotate-key.
- Use streaming APIs to encrypt/decrypt files without loading whole file in memory.
Pseudo-code for file encryption:
// generate AES key and IV SecretKey aes = JCrypter.generateAesKey(256); byte[] iv = JCrypter.generateIv(12); // stream encrypt file to output try (InputStream in = Files.newInputStream(inputPath); OutputStream out = Files.newOutputStream(outputPath)) { out.write(iv); JCrypter.streamEncryptAesGcm(aes, iv, in, out, aad); } // encrypt AES key with RSA byte[] encryptedKey = JCrypter.encryptRsaOaep(userPub, aes.getEncoded()); Files.write(keyPath, encryptedKey); 10. Conclusion
JCrypter (as outlined) simplifies common crypto tasks by providing high‑level APIs for AES‑GCM, RSA‑OAEP, and RSA‑PSS, plus helpers for key generation and streaming. Follow best practices: use AEAD, unique IVs, secure key storage, and validated libraries/providers.
If you want, I can convert examples into a runnable Maven project, add a complete CLI example, or expand any section into code you can compile.