Java实现DES加密解密算法，从键盘输入明文密文

Java可以使用JCE(Java Cryptography Extension)提供的API实现DES加密解密算法，以下是一个简单的示例：

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import java.util.Scanner;

public class DesDemo {

    public static void main(String[] args) throws Exception {
        Scanner scanner = new Scanner(System.in);
        System.out.print("请输入明文：");
        String plainText = scanner.nextLine();
        System.out.print("请输入密钥（8个字符）：");
        String key = scanner.nextLine();

        byte[] encrypted = encrypt(plainText, key);
        System.out.println("加密后的密文：" + new String(encrypted));
        String decrypted = decrypt(encrypted, key);
        System.out.println("解密后的明文：" + decrypted);
    }

    private static byte[] encrypt(String plainText, String key) throws Exception {
        // 生成密钥
        KeyGenerator keyGenerator = KeyGenerator.getInstance("DES");
        keyGenerator.init(56);
        SecretKey secretKey = keyGenerator.generateKey();

        // 加密
        Cipher cipher = Cipher.getInstance("DES");
        cipher.init(Cipher.ENCRYPT_MODE, secretKey);
        byte[] encrypted = cipher.doFinal(plainText.getBytes());

        return encrypted;
    }

    private static String decrypt(byte[] encrypted, String key) throws Exception {
        // 生成密钥
        KeyGenerator keyGenerator = KeyGenerator.getInstance("DES");
        keyGenerator.init(56);
        SecretKey secretKey = keyGenerator.generateKey();

        // 解密
        Cipher cipher = Cipher.getInstance("DES");
        cipher.init(Cipher.DECRYPT_MODE, secretKey);
        byte[] decrypted = cipher.doFinal(encrypted);

        return new String(decrypted);
    }
}

在上述代码中，我们通过 `KeyGenerator` 生成了一个 DES 密钥，并使用 `Cipher` 对象实现了 DES 加密和解密。注意，为了确保安全性，DES 的密钥长度必须为 8 个字符，否则会抛出异常。