Java加密和解密函数的实现方法

在Java中，加密和解密是通过使用各种加密算法来保护敏感信息的常见方法。下面将介绍几种常用的加密和解密函数的实现方法。

1. 对称加密算法：对称加密算法使用相同的密钥进行加密和解密。下面是一个示例，使用AES算法进行对称加密和解密。

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;
import java.security.NoSuchAlgorithmException;
import java.util.Base64;

public class SymmetricEncryption {
    public static String encrypt(String message, SecretKey secretKey) throws Exception {
        Cipher cipher = Cipher.getInstance("AES");
        cipher.init(Cipher.ENCRYPT_MODE, secretKey);
        byte[] encryptedBytes = cipher.doFinal(message.getBytes());
        return Base64.getEncoder().encodeToString(encryptedBytes);
    }

    public static String decrypt(String encryptedMessage, SecretKey secretKey) throws Exception {
        Cipher cipher = Cipher.getInstance("AES");
        cipher.init(Cipher.DECRYPT_MODE, secretKey);
        byte[] decryptedBytes = cipher.doFinal(Base64.getDecoder().decode(encryptedMessage));
        return new String(decryptedBytes);
    }

    public static void main(String[] args) throws Exception {
        // 生成密钥
        KeyGenerator keyGenerator = KeyGenerator.getInstance("AES");
        keyGenerator.init(128);
        SecretKey secretKey = keyGenerator.generateKey();

        String message = "Hello, World!";
        String encryptedMessage = encrypt(message, secretKey);
        System.out.println("Encrypted Message: " + encryptedMessage);

        String decryptedMessage = decrypt(encryptedMessage, secretKey);
        System.out.println("Decrypted Message: " + decryptedMessage);
    }
}

2. 非对称加密算法：非对称加密算法使用一对密钥（公钥和私钥）进行加密和解密。下面是一个使用RSA算法的示例。

import java.nio.charset.StandardCharsets;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.Signature;

public class AsymmetricEncryption {
    public static byte[] encrypt(byte[] message, PublicKey publicKey) throws Exception {
        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.ENCRYPT_MODE, publicKey);
        return cipher.doFinal(message);
    }

    public static byte[] decrypt(byte[] encryptedMessage, PrivateKey privateKey) throws Exception {
        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.DECRYPT_MODE, privateKey);
        return cipher.doFinal(encryptedMessage);
    }

    public static byte[] sign(byte[] message, PrivateKey privateKey) throws Exception {
        Signature signature = Signature.getInstance("SHA256withRSA");
        signature.initSign(privateKey);
        signature.update(message);
        return signature.sign();
    }

    public static boolean verify(byte[] message, byte[] signature, PublicKey publicKey) throws Exception {
        Signature verifier = Signature.getInstance("SHA256withRSA");
        verifier.initVerify(publicKey);
        verifier.update(message);
        return verifier.verify(signature);
    }

    public static void main(String[] args) throws Exception {
        // 生成密钥对
        KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");
        keyPairGenerator.initialize(2048);
        KeyPair keyPair = keyPairGenerator.generateKeyPair();

        String message = "Hello, World!";
        byte[] encryptedMessage = encrypt(message.getBytes(StandardCharsets.UTF_8), keyPair.getPublic());
        System.out.println("Encrypted Message: " + new String(encryptedMessage, StandardCharsets.UTF_8));

        byte[] decryptedMessage = decrypt(encryptedMessage, keyPair.getPrivate());
        System.out.println("Decrypted Message: " + new String(decryptedMessage, StandardCharsets.UTF_8));

        byte[] signature = sign(message.getBytes(StandardCharsets.UTF_8), keyPair.getPrivate());
        System.out.println("Signature: " + new String(signature, StandardCharsets.UTF_8));

        boolean isVerified = verify(message.getBytes(StandardCharsets.UTF_8), signature, keyPair.getPublic());
        System.out.println("Is Verified: " + isVerified);
    }
}

3. 哈希函数：哈希函数可以将输入的任意长度数据转换为固定长度的哈希值。下面是一个使用SHA-256算法的示例。

import java.nio.charset.StandardCharsets;
import java.security.MessageDigest;

public class HashFunction {
    public static String hash(String message) throws Exception {
        MessageDigest messageDigest = MessageDigest.getInstance("SHA-256");
        byte[] hashBytes = messageDigest.digest(message.getBytes(StandardCharsets.UTF_8));
        StringBuilder hashBuilder = new StringBuilder();
        for (byte b : hashBytes) {
            hashBuilder.append(String.format("%02x", b));
        }
        return hashBuilder.toString();
    }

    public static void main(String[] args) throws Exception {
        String message = "Hello, World!";
        String hashValue = hash(message);
        System.out.println("Hash Value: " + hashValue);
    }
}

以上是几种常见的加密和解密函数的实现方法，在实际应用中，可以根据具体需求选择合适的算法和密钥长度。同时，对于加解密函数的使用应当注意密钥的保护和安全管理，以确保敏感数据的保密性和完整性。