public class FileUtil
{
	[DllImport("kernel32.dll")]
	private static extern IntPtr _lopen(string lpPathName, int iReadWrite);

	[DllImport("kernel32.dll")]
	public static extern bool CloseHandle(IntPtr hHandle);


	private const int OF_READWRITE = 2;
	private const int OF_SHARE_DENY_NONE = 0x40;
	private static readonly IntPtr HFILE_ERROR = new IntPtr(-1);
	
	/// <summary>
	/// 查看文件是否被占用
	/// </summary>
	/// <param name="filePath">文件路径</param>
	/// <returns></returns>
	public static bool IsOccupied(string filePath)
	{
		IntPtr vHandle = _lopen(filePath, OF_READWRITE | OF_SHARE_DENY_NONE);
		if(vHandle == HFILE_ERROR)
		{
			return true;
		}
		CloseHandle(vHandle);
		return false;
	}
}

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

namespace Utility.Security
{
    /// <summary>
    /// DES加密/解密类。
    /// </summary>
    public class DESEncrypt
    {
        /// <summary> 
        /// 加密数据 
        /// </summary> 
        public static string Encrypt(string Text, string sKey)
        {
            DESCryptoServiceProvider des = new DESCryptoServiceProvider();
            byte[] inputByteArray;
            inputByteArray = Encoding.Default.GetBytes(Text);
            des.Key = ASCIIEncoding.ASCII.GetBytes(System.Web.Security.FormsAuthentication.HashPasswordForStoringInConfigFile(sKey, "md5").Substring(0, 8));
            des.IV = ASCIIEncoding.ASCII.GetBytes(System.Web.Security.FormsAuthentication.HashPasswordForStoringInConfigFile(sKey, "md5").Substring(0, 8));
            System.IO.MemoryStream ms = new System.IO.MemoryStream();
            CryptoStream cs = new CryptoStream(ms, des.CreateEncryptor(), CryptoStreamMode.Write);
            cs.Write(inputByteArray, 0, inputByteArray.Length);
            cs.FlushFinalBlock();
            StringBuilder ret = new StringBuilder();
            foreach (byte b in ms.ToArray())
            {
                ret.AppendFormat("{0:X2}", b);
            }
            return ret.ToString();
        }

        /// <summary> 
        /// 解密数据 
        /// </summary> 
        public static string Decrypt(string Text, string sKey)
        {
            DESCryptoServiceProvider des = new DESCryptoServiceProvider();
            int len;
            len = Text.Length / 2;
            byte[] inputByteArray = new byte[len];
            int x, i;
            for (x = 0; x < len; x++)
            {
                i = Convert.ToInt32(Text.Substring(x * 2, 2), 16);
                inputByteArray[x] = (byte)i;
            }
            des.Key = ASCIIEncoding.ASCII.GetBytes(System.Web.Security.FormsAuthentication.HashPasswordForStoringInConfigFile(sKey, "md5").Substring(0, 8));
            des.IV = ASCIIEncoding.ASCII.GetBytes(System.Web.Security.FormsAuthentication.HashPasswordForStoringInConfigFile(sKey, "md5").Substring(0, 8));
            System.IO.MemoryStream ms = new System.IO.MemoryStream();
            CryptoStream cs = new CryptoStream(ms, des.CreateDecryptor(), CryptoStreamMode.Write);
            cs.Write(inputByteArray, 0, inputByteArray.Length);
            cs.FlushFinalBlock();
            return Encoding.Default.GetString(ms.ToArray());
        }
    }
}