贴别人的一个文件加密程序！

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using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Security.Cryptography;
using System.IO;

namespace WindowsFormsApplication1
{
    public static class abc
    {
        private static byte[] Keys = { 0x12, 0x34, 0x56, 0x78, 0x90, 0xAB, 0xCD, 0xEF };
        /**////   <summary>   
        ///   利用MD5对字符串进行加密   
        ///   </summary>   
        ///   <param   name="someStr">待加密的字符串</param>   
        ///   <returns>返回加密后的字符串</returns>   
        public static string EncryptMD5(string encryptStr)
        {
            MD5CryptoServiceProvider md5Hasher = new MD5CryptoServiceProvider();
            UTF8Encoding Encode = new UTF8Encoding();
            byte[] HashedBytes = md5Hasher.ComputeHash(Encode.GetBytes(encryptStr));
            return Encode.GetString(HashedBytes);
        }

        /**////   <summary>   
        ///   DES加密字符串   
        ///   </summary>   
        ///   <param   name="encryptStr">待加密的字符串</param>   
        ///   <param   name="encryptKey">加密密钥,要求为8位</param>   
        ///   <returns>加密成功返回加密后的字符串，失败返回源串</returns>   
        public static string EncryptDES(string encryptStr, string encryptKey)
        {
            try
            {
                byte[] rgbKey = Encoding.UTF8.GetBytes(encryptKey.Substring(0, 8));
                byte[] rgbIV = Keys;
                byte[] inputByteArray = Encoding.UTF8.GetBytes(encryptStr);
                DESCryptoServiceProvider dCSP = new DESCryptoServiceProvider();
                MemoryStream mStream = new MemoryStream();
                CryptoStream cStream = new CryptoStream(mStream, dCSP.CreateEncryptor(rgbKey, rgbIV), CryptoStreamMode.Write);
                cStream.Write(inputByteArray, 0, inputByteArray.Length);
                cStream.FlushFinalBlock();
                return Convert.ToBase64String(mStream.ToArray());
            }
            catch
            {
                return encryptStr;
            }
        }

        /**////   <summary>   
        ///   DES解密字符串   
        ///   </summary>   
        ///   <param   name="decryptStr">待解密的字符串</param>   
        ///   <param   name="decryptKey">解密密钥,要求为8位,和加密密钥相同</param>   
        ///   <returns>解密成功返回解密后的字符串，失败返源串</returns>   
        public static string DecryptDES(string decryptStr, string decryptKey)
        {
            try
            {
                byte[] rgbKey = Encoding.UTF8.GetBytes(decryptKey);
                byte[] rgbIV = Keys;
                byte[] inputByteArray = Convert.FromBase64String(decryptStr);
                DESCryptoServiceProvider DCSP = new DESCryptoServiceProvider();
                MemoryStream mStream = new MemoryStream();
                CryptoStream cStream = new CryptoStream(mStream, DCSP.CreateDecryptor(rgbKey, rgbIV), CryptoStreamMode.Write);
                cStream.Write(inputByteArray, 0, inputByteArray.Length);
                cStream.FlushFinalBlock();
                return Encoding.UTF8.GetString(mStream.ToArray());
            }
            catch
            {
                return decryptStr;
            }
        }

        /**////   <summary>   
        ///   DES加密文件   
        ///   </summary>   
        ///   <param   name="inFilePath">待加密文件</param>   
        ///   <param   name="outFilePath">加密后的文件</param>   
        ///   <param   name="encryptKey">加密密钥</param>   
        ///   <returns></returns>   
        public static bool EncryptDES(string inFilePath, string outFilePath, string encryptKey)
        {
            byte[] rgbIV = Keys;
            try
            {
                byte[] rgbKey = Encoding.UTF8.GetBytes(encryptKey.Substring(0, 8));
                //读入的流   
                FileStream inFs = new FileStream(inFilePath, FileMode.Open, FileAccess.Read);
                //待写的流   
                FileStream outFs = new FileStream(outFilePath, FileMode.OpenOrCreate, FileAccess.Write);
                outFs.SetLength(0);
                //创建一个变量来帮助读写   
                byte[] byteIn = new byte[100];   //临时存放读入的流   
                long readLen = 0;                             //读入流的长度   
                long totalLen = inFs.Length;         //总共读入流的长度   
                int everyLen;                                     //每次读入流动长度   
                //读入InFs，加密后写入OutFs   
                DES des = new DESCryptoServiceProvider();
                CryptoStream encStream = new CryptoStream(outFs, des.CreateEncryptor(rgbKey, rgbIV), CryptoStreamMode.Write);
                while (readLen < totalLen)
                {
                    everyLen = inFs.Read(byteIn, 0, 100);
                    encStream.Write(byteIn, 0, everyLen);
                    readLen = readLen + everyLen;
                }
                encStream.Close();
                outFs.Close();
                inFs.Close();
                return true;//加密成功   
            }
            catch
            {
                return false;//加密失败     
            }
        }


        /**////   <summary>   
        ///   DES解密文件   
        ///   </summary>   
        ///   <param   name="inFilePath">待解密文件</param>   
        ///   <param   name="outFilePath">待加密文件</param>   
        ///   <param   name="decryptKey">解密密钥</param>   
        ///   <returns></returns>   
        public static bool DecryptDES(string inFilePath, string outFilePath, string decryptKey)
        {
            byte[] rgbIV = Keys;
            try
            {
                byte[] rgbKey = Encoding.UTF8.GetBytes(decryptKey.Substring(0, 8));
                //读入的流   
                FileStream inFs = new FileStream(inFilePath, FileMode.Open, FileAccess.Read);
                //待写的流   
                FileStream outFs = new FileStream(outFilePath, FileMode.OpenOrCreate, FileAccess.Write);
                outFs.SetLength(0);
                //创建一个变量来帮助读写   
                byte[] byteIn = new byte[100];   //临时存放读入的流   
                long readLen = 0;                //读入流的长度   
                long totalLen = inFs.Length;     //总共读入流的长度   
                int everyLen;                    //每次读入流动长度   
                //读入InFs，解密后写入OutFs   
                DES des = new DESCryptoServiceProvider();
                CryptoStream encStream = new CryptoStream(outFs, des.CreateDecryptor(rgbKey, rgbIV), CryptoStreamMode.Write);
                while (readLen < totalLen)
                {
                    everyLen = inFs.Read(byteIn, 0, 100);
                    encStream.Write(byteIn, 0, everyLen);
                    readLen = readLen + everyLen;
                }
                encStream.Close();
                outFs.Close();
                inFs.Close();
                return true;//解密成功   
            }
            catch{
                return false;//解密失败     
            }
        }
    }
}