using System;
using System.IO;
using System.Security.Cryptography;
using System.Text;

namespace ConsoleApp_PreventFileTampering
{
    class Program
    {
        static void Main(string[] args)
        {
            //TestGetFileHash();

            TestGetMd5();
        }

        #region 通过Hash值来验证文件是否被篡改

        public static void TestGetFileHash()
        {
            string fileHash = "";
            while (true)
            {
                fileHash = GetFileHash(@"C:\error.txt");
                Console.WriteLine("文件MD5-HASH值为：{0}", fileHash);
                Console.ReadKey();
                //手动修改文件试试，HASH值会变化
                //手动将刚才的修改恢复，HASH值会还原
            }
        }

        /// <summary>
        /// 通过Hash值来验证文件是否被篡改
        /// </summary>
        /// <param name="argFilePath">文件路径</param>
        /// <returns>输出Hash值</returns>
        public static string GetFileHash(string argFilePath)
        {
            using (MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider())
            using (FileStream fs = new FileStream(argFilePath, FileMode.Open, FileAccess.Read, FileShare.Read))
            {
                return BitConverter.ToString(md5.ComputeHash(fs)).Replace("-", "");
            }
        }

        #endregion

        #region 对字符串用MD5加密

        public static void TestGetMd5()
        {
            while (true)
            {
                Console.WriteLine("输入要加密的字符串：");
                string input = Console.ReadLine();
                string md5 = GetMd5Hash2(input);
                Console.WriteLine("输出的加密字符串为：" + md5 + "\r\n");
                Console.ReadLine();
            }
        }

        /// <summary>
        /// 将字符串转换成MD5值存储
        /// 【直接使用本方法加密MD5是不安全的，可以通过穷举法获得加密前的字符串】
        /// </summary>
        /// <param name="argInput">输入的字符串</param>
        /// <returns>输出的MD5值</returns>
        public static string GetMd5Hash(string argInput)
        {
            using (MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider())
            {
                return BitConverter.ToString(md5.ComputeHash(UTF8Encoding.Default.GetBytes(argInput))).Replace("-", "");
            }
        }

        /// <summary>
        /// 多次使用MD5值以及内部拼hashKey法，增加穷举破解的难度
        /// </summary>
        /// <param name="argInput">输入的字符串</param>
        /// <returns>输出特殊处理过的MD5值</returns>
        public static string GetMd5Hash2(string argInput)
        {
            string hashKey = "Kae@#$@!,.Js+{f>.294oE";
            using (MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider())
            {
                string hashCode = BitConverter.ToString(md5.ComputeHash(UTF8Encoding.Default.GetBytes(argInput)))
                    .Replace("-", "")
                      + BitConverter.ToString(md5.ComputeHash(UTF8Encoding.Default.GetBytes(hashKey)))
                    .Replace("-", "");

                return BitConverter.ToString(md5.ComputeHash(UTF8Encoding.Default.GetBytes(hashCode))).Replace("-", "");
            }
        }

        #endregion

    }
}