DES加密解密帮助类

    public class DESCrypto
    {
        /// <summary>
        /// 初始化des实例秘钥及向量
        /// </summary>
        /// <param name="key"></param>
        /// <returns></returns>
        private static DESCryptoServiceProvider InitDESInstance(string key)
        {
            DESCryptoServiceProvider des = new DESCryptoServiceProvider();
            byte[] salt = new byte[] { 0x0A, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0xF1 };
            byte[] keyByte = Encoding.UTF8.GetBytes(key);
            Rfc2898DeriveBytes rfcKey = new Rfc2898DeriveBytes(keyByte, salt, 8);
            Rfc2898DeriveBytes rfcIv = new Rfc2898DeriveBytes("0987654321", salt, 8);
            des.Key = rfcKey.GetBytes(8);
            des.IV = rfcIv.GetBytes(8);
            return des;
        }

        #region 基于Base64的加密解密（不其他格式的加解密方法配合使用）
        /// <summary>
        /// 基于Base64
        /// </summary>
        /// <param name="plaintext"></param>
        /// <param name="key"></param>
        /// <returns></returns>
        public static string DESEncryptBase64(string plaintext,string key)
        {
            DESCryptoServiceProvider des = InitDESInstance(key);
            byte[] dataByteArray = Encoding.UTF8.GetBytes(plaintext);
            string ciphertext = "";
            using (MemoryStream ms = new MemoryStream())
            using (CryptoStream cs = new CryptoStream(ms, des.CreateEncryptor(), CryptoStreamMode.Write))
            {
                cs.Write(dataByteArray, 0, dataByteArray.Length);
                cs.FlushFinalBlock();
                ciphertext = Convert.ToBase64String(ms.ToArray());
            }
            return ciphertext;
        }

        /// <summary>
        /// 基于Base64
        /// </summary>
        /// <param name="encrypt"></param>
        /// <param name="key"></param>
        /// <returns></returns>
        public static string DESDecryptBase64(string encrypt, string key)
        {
            DESCryptoServiceProvider des = InitDESInstance(key);
            byte[] dataByteArray = Convert.FromBase64String(encrypt);
            using (MemoryStream ms = new MemoryStream())
            using (CryptoStream cs = new CryptoStream(ms, des.CreateDecryptor(), CryptoStreamMode.Write))
            {
                cs.Write(dataByteArray, 0, dataByteArray.Length);
                cs.FlushFinalBlock();
                return Encoding.UTF8.GetString(ms.ToArray());
            }
        }
        #endregion

        #region 基于2位十六进制格式的加密解密（不其他格式的加解密方法配合使用）
        /// <summary>
        /// 加密
        /// </summary>
        /// <param name="plaintext">明文</param>
        /// <param name="key"></param>
        /// <returns></returns>
        public static string DESEncrypt(string plaintext, string key)
        {
            DESCryptoServiceProvider des = InitDESInstance(key);
            StringBuilder sb = new StringBuilder();
            byte[] dataByteArray = Encoding.UTF8.GetBytes(plaintext);
            string ciphertext = "";
            using (MemoryStream ms = new MemoryStream())
            using (CryptoStream cs = new CryptoStream(ms, des.CreateEncryptor(), CryptoStreamMode.Write))
            {
                cs.Write(dataByteArray, 0, dataByteArray.Length);
                cs.FlushFinalBlock();
                //输出加密文本
                foreach (byte b in ms.ToArray())
                {
                    sb.AppendFormat("{0:X2}", b);
                }
                ciphertext = sb.ToString();
            }
            return ciphertext;

        }

        /// <summary>
        /// 解密
        /// </summary>
        /// <param name="ciphertext">密文</param>
        /// <param name="key"></param>
        /// <returns></returns>
        public static string DESDecrypt(string ciphertext, string key)
        {
            DESCryptoServiceProvider des = InitDESInstance(key);
            byte[] dataByteArray = new byte[ciphertext.Length / 2];
            for (int x = 0; x < ciphertext.Length / 2; x++)
            {
                int i = (Convert.ToInt32(ciphertext.Substring(x * 2, 2), 16));
                dataByteArray[x] = (byte)i;
            }
            using (MemoryStream ms = new MemoryStream())
            using (CryptoStream cs = new CryptoStream(ms, des.CreateDecryptor(), CryptoStreamMode.Write))
            {
                cs.Write(dataByteArray, 0, dataByteArray.Length);
                cs.FlushFinalBlock();
                return Encoding.UTF8.GetString(ms.ToArray());
            }
        }
        #endregion

        #region 文件加密解密（不其他格式的加解密方法配合使用）
        /// <summary>
        /// 加密文件
        /// </summary>
        /// <param name="sourceFile">文件的物理路径</param>
        /// <param name="encryptFile">文件的物理路径</param>
        /// <param name="key"></param>
        public static void DESEncryptFile(string sourceFile, string encryptFile, string key)
        {
            if (string.IsNullOrEmpty(sourceFile) || string.IsNullOrEmpty(encryptFile)||!File.Exists(sourceFile)) return;
            
            DESCryptoServiceProvider des = InitDESInstance(key);

            using (FileStream sourceStream = new FileStream(sourceFile, FileMode.Open, FileAccess.Read))
            using (FileStream encryptStream = new FileStream(encryptFile, FileMode.Create, FileAccess.Write))
            {
                byte[] dataByteArray = new byte[sourceStream.Length];
                sourceStream.Read(dataByteArray, 0, dataByteArray.Length);
                using (CryptoStream cs = new CryptoStream(encryptStream, des.CreateEncryptor(), CryptoStreamMode.Write))
                {
                    cs.Write(dataByteArray, 0, dataByteArray.Length);
                    cs.FlushFinalBlock();
                }
            }
        }

        /// <summary>
        /// 解密文件
        /// </summary>
        /// <param name="encryptFile">文件的物理路径</param>
        /// <param name="decryptFile">文件的物理路径</param>
        /// <param name="key"></param>
        public static void DESDecryptFile(string encryptFile, string decryptFile, string key)
        {
            if (string.IsNullOrEmpty(encryptFile) || string.IsNullOrEmpty(decryptFile) || !File.Exists(encryptFile))return;

            DESCryptoServiceProvider des = InitDESInstance(key);

            using (FileStream encryptStream = new FileStream(encryptFile, FileMode.Open, FileAccess.Read))
            using (FileStream decryptStream = new FileStream(decryptFile, FileMode.Create, FileAccess.Write))
            {
                byte[] dataByteArray = new byte[encryptStream.Length];
                encryptStream.Read(dataByteArray, 0, dataByteArray.Length);
                using (CryptoStream cs = new CryptoStream(decryptStream, des.CreateDecryptor(), CryptoStreamMode.Write))
                {
                    cs.Write(dataByteArray, 0, dataByteArray.Length);
                    cs.FlushFinalBlock();
                }
            }
        }

        /// <summary>
        /// 加密文本并输出到文件
        /// </summary>
        /// <param name="plaintext"></param>
        /// <param name="FileName">文件的物理路径</param>
        /// <param name="Key"></param>
        public static void DESEncryptTextToFile(string plaintext, string FileName, string key)
        {
            if (string.IsNullOrEmpty(FileName)) return;

            DESCryptoServiceProvider des = InitDESInstance(key);
            byte[] dataByteArray = Encoding.UTF8.GetBytes(plaintext);

            using (FileStream fStream = File.Open(FileName, FileMode.Create))
            using (CryptoStream cStream = new CryptoStream(fStream, des.CreateEncryptor(), CryptoStreamMode.Write))
            {
                cStream.Write(dataByteArray, 0, dataByteArray.Length);
                cStream.FlushFinalBlock();
            }
        }

        /// <summary>
        /// 解密文件中的密文并返回
        /// </summary>
        /// <param name="FileName"></param>
        /// <param name="Key"></param>
        /// <returns></returns>
        public static string DESDecryptTextFromFile(string FileName, string key)
        {
            if (string.IsNullOrEmpty(FileName)||!File.Exists(FileName)) return "";

            DESCryptoServiceProvider des = InitDESInstance(key);

            using (FileStream fStream = File.Open(FileName, FileMode.OpenOrCreate))
            using (CryptoStream cStream = new CryptoStream(fStream, des.CreateDecryptor(), CryptoStreamMode.Read))
            using (StreamReader sReader = new StreamReader(cStream))
            {
                string val = sReader.ReadToEnd();
                return val;
            }
        }
        #endregion
    }

Tips：参考MSDN整理编写，比较全面。