Generate MD5 checksum from file

Sometimes we have the necessity to verify that the file we downloded wasn’t corrupted. A way to do this it’s to generate a MD5 checksum and verify the file integrity.

The purpose of this check is to establish that the file has not been modified by someone.

        public string GetMD5HashFromFile(string fileName)
        {
            FileStream file = new FileStream(fileName, FileMode.Open);
            MD5 md5 = new MD5CryptoServiceProvider();
            byte[] retVal = md5.ComputeHash(file);
            file.Close();

            StringBuilder sb = new StringBuilder();
            for (int i = 0; i < retVal.Length; i++)
            {
                sb.Append(retVal[i].ToString("x2"));
            }

            string checksum = sb.ToString();

            return checksum;
        }

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