说明

1. 通过调用Encode方法，可将str加密成content，返回一个int值作为本次加密内容的标记。
2. 通过调用TryDecode，传入加密内容content，若可解密（content格式满足要求），则解出str，并得到content的int标记。

代码

FanStrCoder.cs
提供2个方法：Encode、TryDecode

using System.Text;
using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using Unity.VisualScripting;
using System.Security.Cryptography;
using System.IO;
using System.Diagnostics;

/// <summary>
/// 对string进行加密和解密
/// </summary>
public static class FanStrCoder
{
    private const string SignSeparator = "_";
    private const byte SimpleKey = 0xFF;
    private static int CreateSign()
    {
        var str = DateTime.Now.Ticks.ToString();
        var length = str.Length;
        var subStr = str.Substring(length - 5, 5);
        var ret = int.Parse(subStr);
        return ret;
    }
    public static int Encode(string str, out string content)
    {
        var sign = CreateSign();
        var strWithSign = sign.ToString() + SignSeparator + str;
        content = EncryptDES(strWithSign, string.Empty);
        return sign;
    }
    public static bool TryDecode(string str, out int sign, out string content)
    {
        sign = 0;
        content = string.Empty;
        var strWithSign = DecryptDES(str, string.Empty);
        var strWithSigns = strWithSign.Split(SignSeparator);
        var signStr = strWithSigns[0];
        var ret = int.TryParse(signStr, out sign);
        if (ret)
        {
            content = strWithSign.Substring(signStr.Length + 1);
        }
        return ret;
    }

    private static Encoding Encoding => Encoding.UTF8;

    private static string EncryptDES(string encryptString, string key)
    {
        var input = Encoding.GetBytes(encryptString);
        var ouptputData = ProcessDES(input, key, true);
        var outputStr = Convert.ToBase64String(ouptputData);

        //base64编码中有不能作为文件名的'/'符号，这里把它替换一下，增强适用范围
        return outputStr.Replace('/', '@');
    }

    private static string DecryptDES(string decryptString, string key)
    {
        decryptString = decryptString.Replace('@', '/');
        try
        {
            var input = Convert.FromBase64String(decryptString);
            var data = ProcessDES(input, key, false);
            return Encoding.GetString(data);
        }
        catch (FormatException)
        {
            UnityEngine.Debug.LogError(nameof(DecryptDES) + ":字符串格式错误！");
            return string.Empty;
        }
    }


    private static byte[] ProcessDES(byte[] data, string key, bool isEncrypt)
    {
        using var dCSP = new DESCryptoServiceProvider();
        var keyData = Md5(key);
        var rgbKey = new ArraySegment<byte>(keyData, 0, 8).ToArray();
        var rgbIV = new ArraySegment<byte>(keyData, 8, 8).ToArray();
        var dCSPKey = isEncrypt ? dCSP.CreateEncryptor(rgbKey, rgbIV) : dCSP.CreateDecryptor(rgbKey, rgbIV);

        using var memory = new MemoryStream();
        using var cStream = new CryptoStream(memory, dCSPKey, CryptoStreamMode.Write);
        cStream.Write(data, 0, data.Length);
        cStream.FlushFinalBlock();
        return memory.ToArray();
    }

    public static byte[] Md5(string str)
    {
        using var md5 = MD5.Create();
        return md5.ComputeHash(Encoding.UTF8.GetBytes(str));
    }
}

FanTest.cs
说明用法

using UnityEngine;

public class FanTest : MonoBehaviour
{
    [SerializeField, TextArea]
    private string _needEncodeStr;
    [SerializeField, TextArea]
    private string _needDecodeStr;

    private void Start()
    {

    }

    private void OnDestroy()
    {

    }

    private void Update()
    {
        if (Input.GetKeyDown(KeyCode.A))
        {
            var needEncodeStr = _needEncodeStr;
            var sign = FanStrCoder.Encode(needEncodeStr, out string str);
            Debug.Log("加密：" + sign + "\n" + str);
        }
        else if (Input.GetKeyUp(KeyCode.B))
        {
            var needDecodeStr = _needDecodeStr;
            if (FanStrCoder.TryDecode(needDecodeStr, out int sign, out string str))
            {
                Debug.Log("解密成功：" + sign + "\n" + str);
            }
            else
            {
                Debug.Log("解密失败");
            }
        }
    }
}