MD5 哈希计算工具类

MD5相当于文件指纹，比较文件是否被修改很有用．常见的文件升级，病毒检测应该就是用这种技术．

现实代码如下：

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

namespace CodeLib.Security
{
    /// <summary>
    /// MD5 哈希计算工具类，能从字符串和文件中计算哈希值。
    /// 支持MD5和SHA1两种算法，可指定大小写。
    /// </summary>
    public sealed class MD5Utils
    {
        public string GetMD5FromString(string value)
        {
            return GetMD5FromString(value, false);
        }

        public string GetMD5FromString(string value, bool returnlowerCase)
        {            
            MD5 md5 = MD5.Create();
            byte[] data = md5.ComputeHash(System.Text.Encoding.Default.GetBytes(value));
            StringBuilder sbResult = new StringBuilder();
            for (int i = 0; i < data.Length; i++)
            {
                if (returnlowerCase)
                {
                    sbResult.AppendFormat("{0:x2}", data[i]);
                }
                else
                {
                    sbResult.AppendFormat("{0:X2}", data[i]);
                }
            }
            return sbResult.ToString();
        }

        public string GetMD5FromFile(string fileName)
        {
            return GetMD5FromFile(fileName, false);
        }

        public string GetMD5FromFile(string fileName, bool returnlowerCase)
        {
            using (System.IO.FileStream fileStream 
                = new System.IO.FileStream(fileName, System.IO.FileMode.Open, System.IO.FileAccess.Read))
            {
                MD5 md5 = MD5.Create();
                byte[] data = md5.ComputeHash(fileStream);
                StringBuilder sbResult = new StringBuilder();
                for (int i = 0; i < data.Length; i++)
                {
                    if (returnlowerCase)
                    {
                        sbResult.AppendFormat("{0:x2}", data[i]);
                    }
                    else
                    {
                        sbResult.AppendFormat("{0:X2}", data[i]);
                    }
                }
                return sbResult.ToString();
            }            
        }

        public string GetSHA1FromString(string value)
        {
            return GetSHA1FromString(value, false);
        }

        public string GetSHA1FromString(string value, bool returnlowerCase)
        {
            SHA1 md5 = SHA1.Create();
            byte[] data = md5.ComputeHash(System.Text.Encoding.Default.GetBytes(value));
            StringBuilder sbResult = new StringBuilder();
            for (int i = 0; i < data.Length; i++)
            {
                if (returnlowerCase)
                {
                    sbResult.AppendFormat("{0:x2}", data[i]);
                }
                else
                {
                    sbResult.AppendFormat("{0:X2}", data[i]);
                }
            }
            return sbResult.ToString();
        }

        public string GetSHA1FromFile(string fileName)
        {
            return GetSHA1FromFile(fileName, false);
        }

        public string GetSHA1FromFile(string fileName, bool returnlowerCase)
        {
            using (System.IO.FileStream fileStream
                = new System.IO.FileStream(fileName, System.IO.FileMode.Open, System.IO.FileAccess.Read))
            {
                SHA1 md5 = SHA1.Create();
                byte[] data = md5.ComputeHash(fileStream);
                StringBuilder sbResult = new StringBuilder();
                for (int i = 0; i < data.Length; i++)
                {
                    if (returnlowerCase)
                    {
                        sbResult.AppendFormat("{0:x2}", data[i]);
                    }
                    else
                    {
                        sbResult.AppendFormat("{0:X2}", data[i]);
                    }
                }
                return sbResult.ToString();
            }
        }
    }
}

测试：

/// <summary>
       ///A test for GetMD5FromFile
       ///</summary>
       [TestMethod()]
       public void GetMD5FromFileTest()
       {
           MD5Utils target = new MD5Utils(); 
           string fileName = @"C:\WINDOWS\NOTEPAD.EXE"; 
           string expected = string.Empty; 
           string actual;
           actual = target.GetMD5FromFile(fileName);
           Console.WriteLine(actual);            
       }

输出：CA94F7297B444AB655CD4B7793C02FD3

如果你输出的不是这个值，估计是中病毒了：）