一、RC4加密算法

在密码学中，RC4（来自Rivest Cipher 4的缩写）是一种流加密算法，密钥长度可变。它加解密使用相同的密钥，因此也属于对称加密算法。

百度百科 - RC4：https://baike.baidu.com/item/RC4/3454548?fr=ge_ala

二、Rc4Utils工具类

1、方式一

下面 Rc4Utils 提供了针对文本内容、字节数组内容的加解密实现。使用加密算法实现。

import org.apache.commons.codec.binary.Base64;

import java.nio.charset.StandardCharsets;
import java.util.Arrays;

public class Rc4Utils {

    /**
     * 对文本内容进行加密.
     *
     * @param plainText 待加密明文内容.
     * @param rc4Key    RC4密钥.
     * @return 加密的密文.
     */
    public static String encodeText(String plainText, String rc4Key) {
        byte[] plainBytes = plainText.getBytes(StandardCharsets.UTF_8);
        byte[] cipherBytes = rc4EnOrDecode(plainBytes, rc4Key);
        return Base64.encodeBase64String(cipherBytes);
    }

    /**
     * 对文本密文进行解密.
     *
     * @param cipherText 待解密密文.
     * @param rc4Key     RC4密钥.
     * @return 解密的明文.
     */
    public static String decodeText(String cipherText, String rc4Key) {
        byte[] cipherBytes = Base64.decodeBase64(cipherText);
        byte[] plainBytes = rc4EnOrDecode(cipherBytes, rc4Key);
        return new String(plainBytes, StandardCharsets.UTF_8);
    }

    /**
     * 对字节数组内容进行加密.
     *
     * @param plainBytes 待加密明文内容.
     * @param rc4Key     RC4密钥.
     * @return 加密的密文.
     */
    public static byte[] encodeBytes(byte[] plainBytes, String rc4Key) {
        byte[] cipherBytes = rc4EnOrDecode(plainBytes, rc4Key);
        return cipherBytes;
    }

    /**
     * 对字节数组密文进行解密.
     *
     * @param cipherBytes 待解密密文.
     * @param rc4Key      RC4密钥.
     * @return 解密的明文.
     */
    public static byte[] decodeBytes(byte[] cipherBytes, String rc4Key) {
        byte[] plainBytes = rc4EnOrDecode(cipherBytes, rc4Key);
        return plainBytes;
    }

    /**
     * 初始化RC4密钥.
     *
     * @param rc4Key RC4密钥.
     * @return 初始化后的密钥.
     * @throws Exception 可能的异常.
     */
    private static byte[] rc4InitKey(String rc4Key) {
        byte[] keyBytes = null;
        byte[] keyState = null;
        int indexFirst = 0;
        int indexSecond = 0;
        // 变量初始化.
        keyBytes = rc4Key.getBytes(StandardCharsets.UTF_8);
        keyState = new byte[256];
        for (int i = 0; i < 256; i++) {
            keyState[i] = (byte) i;
        }
        // 进行初始化.
        if (keyBytes == null || keyBytes.length == 0) {
            return null;
        }
        for (int i = 0; i < 256; i++) {
            indexSecond = ((keyBytes[indexFirst] & 0xff) + (keyState[i] & 0xff) + indexSecond) & 0xff;
            byte tmp = keyState[i];
            keyState[i] = keyState[indexSecond];
            keyState[indexSecond] = tmp;
            indexFirst = (indexFirst + 1) % keyBytes.length;
        }
        return keyState;
    }

    /**
     * RC4算法进行加解密.
     *
     * @param bytes  待处理内容.
     * @param rc4Key RC4密钥.
     * @return 处理后结果内容.
     */
    public static byte[] rc4EnOrDecode(byte[] bytes, String rc4Key) {
        int x = 0;
        int y = 0;
        byte key[] = rc4InitKey(rc4Key);
        int xorIndex;
        byte[] result = new byte[bytes.length];
        // 数据加密.
        for (int i = 0; i < bytes.length; i++) {
            x = (x + 1) & 0xff;
            y = ((key[x] & 0xff) + y) & 0xff;
            byte tmp = key[x];
            key[x] = key[y];
            key[y] = tmp;
            xorIndex = ((key[x] & 0xff) + (key[y] & 0xff)) & 0xff;
            result[i] = (byte) (bytes[i] ^ key[xorIndex]);
        }
        return result;
    }

    public static void main(String[] args) throws Exception {
        //String rc4Key = "1234567890";
        String rc4Key = "78077e1be9204c21ac03cda1e6ea7a01";
        String plainText = "This is 一段明文内容 123 ！";
        String cipherText = null;

        // 文本加解密测试.
        System.out.println("----------------------- 文本加解密测试 -------------------------");
        System.out.println("明文：" + plainText);
        cipherText = Rc4Utils.encodeText(plainText, rc4Key);
        System.out.println("密文：" + cipherText);
        plainText = Rc4Utils.decodeText(cipherText, rc4Key);
        System.out.println("解密明文：" + plainText);
        System.out.println();

        System.out.println("----------------------- 字节数组加解密测试 -------------------------");
        byte[] plainBytes = plainText.getBytes("UTF-8");
        byte[] cipherBytes = null;
        System.out.println("明文：" + Arrays.toString(plainBytes));
        cipherBytes = Rc4Utils.encodeBytes(plainBytes, rc4Key);
        System.out.println("密文：" + Arrays.toString(cipherBytes));
        plainBytes = Rc4Utils.decodeBytes(cipherBytes, rc4Key);
        System.out.println("解密明文：" + Arrays.toString(plainBytes));
        System.out.println();
    }

}

2、方式2

下面 Rc4Utils2 提供了针对文本内容的加解密实现。使用 Java封装好的类实现。

import lombok.extern.slf4j.Slf4j;

import javax.crypto.Cipher;
import javax.crypto.spec.SecretKeySpec;
import java.nio.charset.StandardCharsets;
import java.util.Base64;

@Slf4j
public class Rc4Utils2 {

    /**
     * 对文本内容进行加密.
     *
     * @param plainText 待加密明文内容.
     * @param rc4Key    RC4密钥.
     * @return 加密的密文.
     */
    public static String encodeText(String plainText, String rc4Key) {
        String result = "";
        try {
            Cipher cipher = Cipher.getInstance("RC4");
            SecretKeySpec key = new SecretKeySpec(rc4Key.getBytes(StandardCharsets.UTF_8), "RC4");
            cipher.init(Cipher.DECRYPT_MODE, key);

            byte[] encryptedBytes = cipher.doFinal(plainText.getBytes(StandardCharsets.UTF_8));
            result = Base64.getEncoder().encodeToString(encryptedBytes);
        } catch (Throwable e) {
            log.error(" 加密 encodeText方法异常，e={}", e);
            e.printStackTrace();
        }
        return result;
    }

    /**
     * 对文本密文进行解密.
     *
     * @param cipherText 待解密密文.
     * @param rc4Key     RC4密钥.
     * @return 解密的明文.
     */
    public static String decodeText(String cipherText, String rc4Key) {
        String result = "";
        try {
            Cipher cipher = Cipher.getInstance("RC4");
            SecretKeySpec key = new SecretKeySpec(rc4Key.getBytes(StandardCharsets.UTF_8), "RC4");
            cipher.init(Cipher.DECRYPT_MODE, key);

            byte[] bytesA = Base64.getDecoder().decode(cipherText.getBytes(StandardCharsets.UTF_8));
            result = new String(cipher.update(bytesA), StandardCharsets.UTF_8);
        } catch (Throwable e) {
            log.error(" 解密 decodeText方法异常，e={}", e);
            e.printStackTrace();
        }
        return result;
    }

    public static void main(String[] args) {
        /**
         * rc4Key有长度限制
         * java.security.InvalidKeyException: Illegal key size or default parameters
         */
        //String rc4Key = "78077e1be9204c21ac03cda1e6ea7a01";
        String rc4Key = "1234567890";
        String plainText = "This is 一段明文内容 123 ！";
        String cipherText = null;

        // 文本加解密测试.
        System.out.println("----------------------- 文本加解密测试 -------------------------");
        System.out.println("明文：" + plainText);
        cipherText = Rc4Utils2.encodeText(plainText, rc4Key);
        System.out.println("密文：" + cipherText);
        plainText = Rc4Utils2.decodeText(cipherText, rc4Key);
        System.out.println("解密明文：" + plainText);
        System.out.println();
    }

}

参考文章：

• RC4 加密算法：https://blog.51cto.com/u_15301988/3089450

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