Java.security包完整教程：从消息摘要到数字签名代码实现

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class MessageDigestExample {
    public static void main(String[] args) {
        try {
            String input = "Hello, World!";
            
            // 创建 MD5 消息摘要实例
            MessageDigest md5 = MessageDigest.getInstance("MD5");
            byte[] md5Hash = md5.digest(input.getBytes());
            System.out.println("MD5: " + bytesToHex(md5Hash));
            
            // 创建 SHA-256 消息摘要实例
            MessageDigest sha256 = MessageDigest.getInstance("SHA-256");
            byte[] sha256Hash = sha256.digest(input.getBytes());
            System.out.println("SHA-256: " + bytesToHex(sha256Hash));
            
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        }
    }
    
    // 将字节数组转换为十六进制字符串
    private static String bytesToHex(byte[] bytes) {
        StringBuilder sb = new StringBuilder();
        for (byte b : bytes) {
            sb.append(String.format("%02x", b));
        }
        return sb.toString();
    }
}

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

public class DigitalSignatureExample {
    public static void main(String[] args) {
        try {
            String message = "重要数据需要签名";
            
            // 生成密钥对
            KeyPairGenerator keyGen = KeyPairGenerator.getInstance("RSA");
            keyGen.initialize(2048);
            KeyPair keyPair = keyGen.generateKeyPair();
            PrivateKey privateKey = keyPair.getPrivate();
            PublicKey publicKey = keyPair.getPublic();
            
            // 创建签名对象
            Signature signature = Signature.getInstance("SHA256withRSA");
            
            // 使用私钥签名
            signature.initSign(privateKey);
            signature.update(message.getBytes());
            byte[] digitalSignature = signature.sign();
            
            System.out.println("签名: " + Base64.getEncoder().encodeToString(digitalSignature));
            
            // 使用公钥验证签名
            signature.initVerify(publicKey);
            signature.update(message.getBytes());
            boolean verified = signature.verify(digitalSignature);
            
            System.out.println("签名验证结果: " + verified);
            
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import java.security.SecureRandom;
import java.util.Base64;

public class EncryptionExample {
    public static void main(String[] args) {
        try {
            String plainText = "敏感数据需要加密";
            
            // 生成 AES 密钥
            KeyGenerator keyGen = KeyGenerator.getInstance("AES");
            keyGen.init(128, new SecureRandom());
            SecretKey secretKey = keyGen.generateKey();
            
            // 加密
            Cipher cipher = Cipher.getInstance("AES");
            cipher.init(Cipher.ENCRYPT_MODE, secretKey);
            byte[] encryptedBytes = cipher.doFinal(plainText.getBytes());
            String encryptedText = Base64.getEncoder().encodeToString(encryptedBytes);
            System.out.println("加密后: " + encryptedText);
            
            // 解密
            cipher.init(Cipher.DECRYPT_MODE, secretKey);
            byte[] decryptedBytes = cipher.doFinal(Base64.getDecoder().decode(encryptedText));
            String decryptedText = new String(decryptedBytes);
            System.out.println("解密后: " + decryptedText);
            
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

import java.security.SecureRandom;

public class SecureRandomExample {
    public static void main(String[] args) {
        SecureRandom secureRandom = new SecureRandom();
        
        // 生成随机字节
        byte[] randomBytes = new byte[16];
        secureRandom.nextBytes(randomBytes);
        System.out.println("随机字节: " + bytesToHex(randomBytes));
        
        // 生成随机整数
        int randomInt = secureRandom.nextInt();
        System.out.println("随机整数: " + randomInt);
        
        // 生成指定范围的随机数
        int randomInRange = secureRandom.nextInt(100);
        System.out.println("0-99范围内的随机数: " + randomInRange);
    }
    
    private static String bytesToHex(byte[] bytes) {
        StringBuilder sb = new StringBuilder();
        for (byte b : bytes) {
            sb.append(String.format("%02x", b));
        }
        return sb.toString();
    }
}

import java.io.FileInputStream;
import java.security.KeyStore;
import java.security.PrivateKey;
import java.security.cert.Certificate;

public class KeyStoreExample {
    public static void main(String[] args) {
        try {
            // 加载密钥库
            KeyStore keyStore = KeyStore.getInstance("JKS");
            char[] password = "password".toCharArray();
            FileInputStream fis = new FileInputStream("keystore.jks");
            keyStore.load(fis, password);
            fis.close();
            
            // 获取别名
            String alias = keyStore.aliases().nextElement();
            System.out.println("密钥别名: " + alias);
            
            // 获取私钥
            PrivateKey privateKey = (PrivateKey) keyStore.getKey(alias, password);
            System.out.println("私钥算法: " + privateKey.getAlgorithm());
            
            // 获取证书
            Certificate certificate = keyStore.getCertificate(alias);
            System.out.println("证书类型: " + certificate.getType());
            
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}