// AES-256 加密示例
import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.spec.IvParameterSpec;
import java.util.Base64;

public class AESExample {
  public static void main(String[] args) throws Exception {
    // 生成AES密钥
    KeyGenerator keyGen = KeyGenerator.getInstance("AES");
    keyGen.init(256); // AES-256
    SecretKey secretKey = keyGen.generateKey();

    // 初始化向量
    byte[] iv = new byte[16];
    new SecureRandom().nextBytes(iv);
    IvParameterSpec ivSpec = new IvParameterSpec(iv);

    // 加密
    Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
    cipher.init(Cipher.ENCRYPT_MODE, secretKey, ivSpec);
    String plaintext = "这是一条秘密消息";
    byte[] encrypted = cipher.doFinal(plaintext.getBytes());
    String encryptedString = Base64.getEncoder().encodeToString(encrypted);

    // 解密
    cipher.init(Cipher.DECRYPT_MODE, secretKey, ivSpec);
    byte[] decrypted = cipher.doFinal(Base64.getDecoder().decode(encryptedString));
    String decryptedString = new String(decrypted);

    System.out.println("加密后: " + encryptedString);
    System.out.println("解密后: " + decryptedString);
  }
}

// SHA-256 哈希计算示例
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.nio.charset.StandardCharsets;
import java.util.Base64;

public class SHA256Example {
  public static void main(String[] args) {
    try {
      String input = "Hello, World!";
      MessageDigest digest = MessageDigest.getInstance("SHA-256");
      // 计算哈希值
      byte[] hashBytes = digest.digest(input.getBytes(StandardCharsets.UTF_8));
      // 转换为十六进制字符串
      StringBuilder hexString = new StringBuilder();
      for (byte b : hashBytes) {
        hexString.append(String.format("%02x", b));
      }
      String hash = hexString.toString();
      System.out.println("SHA-256哈希值: " + hash);
      // 输出: a591a6d40bf420404a011733cfb7b190d62c65bf0bcda32b57b277d9ad9f146e
    } catch (NoSuchAlgorithmException e) {
      e.printStackTrace();
    }
  }
}