Detailed explanation of how C# obtains file MD5 and SHA1

When I first started learning programming, I always thought about writing some small software gadgets myself.

And this is the classic file MD5 verification, with a SHA1 added by the way.

When downloading something on the Internet, the author will provide the MD5 value.

Its function is that after downloading the software, we can perform an MD5 check on the downloaded file to ensure that the file we obtain is the same file as the file provided by the site.

So you need an MD5 verification tool, so go to Baidu to find it, but needless to say domestic download sites...the bundled things are hard to guard against.

So, as a programmer, just write one yourself.

The main requirement for analyzing this gadget is

1. Find the file according to the path

2. Get MD5

3. Get SHA1

A very simple small tool,

The first method is to directly use the FileInfo class constructor to pass in the path, because you can drag and drop files directly on the console, which is very convenient.

It should be noted that if there are spaces in the path, an error will be reported.

In this method, s represents the incoming file path

static void GetFile(string s)
        {
            try
            {
                FileInfo fi = new FileInfo(s);
                Console.WriteLine("文件路径：{0}", s);
                Console.WriteLine("文件名称：{0}", fi.Name.ToString());
                Console.WriteLine("文件类型：{0}", fi.Extension.ToString());
                Console.WriteLine("文件大小：{0} K", fi.Length / 1024);
                Console.WriteLine("文件创建时间：{0}", fi.CreationTime.ToString());
                Console.WriteLine("上次访问时间：{0}", fi.LastAccessTime.ToString());
                Console.WriteLine("上次写入时间：{0}", fi.LastWriteTime.ToString());
            }
            catch (Exception ex) 
            {
                Console.WriteLine(ex.Message);
            }
        }

The second method obtains the MD5 value. In this method, s represents the incoming file path.

MD5 converts the entire The file is treated as a large text message, and through its irreversible string transformation algorithm, this unique MD5 message digest is generated.

static void GetMD5(string s)
        {
            try
            {
                FileStream file = new FileStream(s,FileMode.Open);
                MD5 md5 = new MD5CryptoServiceProvider();
                byte[] retval = md5.ComputeHash(file);
                file.Close();

                StringBuilder sc = new StringBuilder();
                for (int i = 0 ; i<retval.Length ; i++ )
                {
                    sc.Append(retval[i].ToString("x2"));
                }
                Console.WriteLine("文件MD5：{0}",sc);
            }
            catch(Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
        }

The third method is to obtain the SHA1 value. In this method, s represents the incoming file path.

SHA1 is called a secure hash algorithm. For messages with a length less than 2^64 bits, SHA1 produces a 160-bit message digest.

SHA1 has the following characteristics: information cannot be recovered from the message digest; two different messages will not produce the same message digest, (but there will be a 1x10^48 chance of the same message digest appearing , ignored in general use).

static void GetSHA1(string s)
        {
            try
            {
                FileStream file = new FileStream(s, FileMode.Open);
                SHA1 sha1 = new SHA1CryptoServiceProvider();
                byte[] retval = sha1.ComputeHash(file);
                file.Close();

                StringBuilder sc = new StringBuilder();
                for (int i = 0; i < retval.Length; i++)
                {
                    sc.Append(retval[i].ToString("x2"));
                }
                Console.WriteLine("文件SHA1：{0}", sc);
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
        }

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