CommonUtil Tutorial

This tutorial provides an overview of the CommonUtil class, which is part of the lightweight-component/aj-util library. The CommonUtil class provides common cryptographic utilities used throughout the library.

Introduction

The CommonUtil class contains static methods for various cryptographic operations including:

• General cipher operations (encryption/decryption)
• XOR encryption/decryption
• Private key loading and management
• Certificate deserialization

Main Features

• Unified cipher operation handling
• Simple XOR encryption/decryption
• Private key loading from various sources
• Certificate deserialization and validation
• Support for multiple cryptographic algorithms

Methods

1. Cipher Operations

1. doCipher(String algorithmName, int mode, Key key, byte[] data) - Basic cipher operation
2. doCipher(String algorithmName, int mode, Key key, byte[] data, AlgorithmParameterSpec spec) - Cipher with parameters
3. doCipher(String algorithmName, int mode, byte[] keyData, AlgorithmParameterSpec spec, String cipherText, byte[] associatedData) - AES cipher with associated data

2. XOR Encryption

1. XOR_encode(String res, String key) - Simple XOR encryption
2. XOR_decode(String res, String key) - XOR decryption
3. XOR(int res, String key) - Integer XOR operation

3. Key Management

1. loadPrivateKeyByPath(String privateKeyPath) - Load private key from file
2. loadPrivateKey(String privateKey) - Load private key from string
3. loadPrivateKey(InputStream inputStream) - Load private key from stream

4. Certificate Handling

1. deserializeToCerts(String apiV3Key, Map<String, Object> pMap) - Deserialize and decrypt certificates

Usage Examples

Cipher Operations

byte[] encrypted = CommonUtil.doCipher("AES/CBC/PKCS5Padding", 
    Cipher.ENCRYPT_MODE, key, data, ivSpec);

String decrypted = CommonUtil.doCipher("AES/GCM/NoPadding",
    Cipher.DECRYPT_MODE, keyBytes, gcmSpec, cipherText, aad);

XOR Encryption

String encoded = CommonUtil.XOR_encode("secret", "password");
String decoded = CommonUtil.XOR_decode(encoded, "password");

Key Loading

PrivateKey key = CommonUtil.loadPrivateKeyByPath("keys/private.pem");
PrivateKey key2 = CommonUtil.loadPrivateKey(privateKeyString);

Certificate Handling

Map<BigInteger, X509Certificate> certs = 
    CommonUtil.deserializeToCerts(apiV3Key, responseMap);

Implementation Notes

• Handles various cryptographic exceptions
• Supports multiple key formats
• Includes basic certificate validation
• Provides simple XOR encryption for basic obfuscation

Conclusion

The CommonUtil class provides foundational cryptographic utilities that are used by other security-related classes in the library, offering consistent handling of common cryptographic operations.