Online MD5 Hash Generator

I'm facing kind of a strange issue which is related MD5-Hashes in Java and php5.I figured that unter certain circumstances the following code does notgenerate correct MD5 hashes:

public static String getMD5Hash(String string){    try     {        MessageDigest md5 = MessageDigest.getInstance("MD5");        md5.update(string.getBytes());        byte[] digest = md5.digest();        string = byteArrToHexString(digest);    }     catch (NoSuchAlgorithmException e1)     {        e1.printStackTrace();    }    return string;}private static String byteArrToHexString(byte[] bArr){    StringBuffer sb = new StringBuffer();    for (int i = 0; i < bArr.length; i++)     {        int unsigned = bArr[i] & 0xff;        sb.append(Integer.toHexString((unsigned)));    }    return sb.toString();}

I had to migrate an existing user database where the passwords where storedin php5 MD5. Now some of the users, not all, can't login because my Java codedoes not produce the correct MD5 hash.

Any ideas what's wrong with the above?

I here am able to generate the MD5 hash of the files in the Google Drive. The next step is I want to like compare those hashes and should there be an identical hash , the program will prevent the application from uploading that file due to the same hash.

I tried declaring a hashset and calling the MD5checksum in the parameters and declaring a function to generate the hash but neither both these are working,

public static List<GoogleDriveFiles> GetDriveFiles()    {        DriveService service = GetService();        // define parameters of request.        FilesResource.ListRequest FileListRequest = service.Files.List();        //listRequest.PageSize = 10;        //listRequest.PageToken = 10;        FileListRequest.Fields = "nextPageToken, files(id, name, size, createdTime, md5Checksum)";        //get file list.        IList<Google.Apis.Drive.v3.Data.File> files = FileListRequest.Execute().Files;        List<GoogleDriveFiles> FileList = new List<GoogleDriveFiles>();        //get hash        if (files != null && files.Count > 0)        {            foreach (var file in files)            {                GoogleDriveFiles File = new GoogleDriveFiles                {                    Id = file.Id,                    Name = file.Name,                    Size = file.Size,                    CreatedTime = file.CreatedTime,                    MD5hash = file.Md5Checksum,            };                FileList.Add(File);            }        }        return FileList;    }

How can I generate like a hashset for those hash values that have been obtained or is there another practical way to store and compare those MD5 hash?

I am trying to generate the hash values of my files in Google Drive. I am confused as I want to generate the hash via the hashing code but after seeing some documentation, I saw there is the calling of md5checksum in the google drive.

//get file list.        IList<Google.Apis.Drive.v3.Data.File> files = FileListRequest.Execute().Files;        List<GoogleDriveFiles> FileList = new List<GoogleDriveFiles>();        if (files != null && files.Count > 0)        {            foreach (var file in files)            {                GoogleDriveFiles File = new GoogleDriveFiles                {                    Id = file.Id,                    Name = file.Name,                    Size = file.Size,                    Version = file.Version,                    CreatedTime = file.CreatedTime,                 //   md5Checksum = file.Md5Checksum,                };                FileList.Add(File);            }        }        return FileList;    }//Get Hash Value     public static void GenerateHash(HttpPostedFileBase file)    {        string directory = Path.Combine(HttpContext.Current.Server.MapPath("~/GoogleDriveFiles"),            Path.GetFileName(file.FileName));        using (var md5 = MD5.Create())        {            using (var stream = File.OpenRead(directory))            {                var hash = md5.ComputeHash(stream);                var data = BitConverter.ToString(hash).Replace("-", "").ToLowerInvariant();            }        }    }

When I ran that code, it showed an error of

invalid field selection md5 checksum at the third line

(List ... )

I tried to run the generate hash code also but there was no hash that was generated by my application. I am unsure on which part I am missing out.

Is there any vulnerability associated with self-hashing?

Let's say I want to keep a database of md5-hashed passwords. The issue is that most people will use easy pws like 'password', 'admin' etc., all prime candidates for reverse md5 lookup services. My idea is to hash the hash i.e.:

password  = 'admin'md5(password) = 0x21232f297a57a5a743894a0e4a801fc3md5(md5(password)) = 0xc3284d0f94606de1fd2af172aba15bf3

In real-life examples we use salts. But is the above even a bad idea, does it really bring inherent flaws?

I here have some code on the implementation of Google Drive Rest API with ASP.net. For now, this have some functionalities such as uploading, downloading, deleting and choosing files. I am using ASP.net and C# for this.

I wanted to create like a data deduplication program with these codes. I wanted to use MD5 hash to hash those files that are in the Google Drive and from there if there is a duplicated hash, then the file will not be selected to be uploaded. It will like generate the hash and compare the hash of files. I am not too sure how to implement this like should I store those MD5 hash in a hashset or hash table.

using Google.Apis.Auth.OAuth2;using Google.Apis.Download;using Google.Apis.Drive.v3;using Google.Apis.Services;using Google.Apis.Util.Store;using System;using System.Collections.Generic;using System.IO;using System.Threading;using System.Web;namespace GoogleDriveRestApi_v3.Models{public class GoogleDriveFilesRepository{    public static string[] Scopes = { DriveService.Scope.Drive };    //create Drive API service.    public static DriveService GetService()    {        //get Credentials from client_secret.json file         UserCredential credential;        using (var stream = new FileStream(@"D:\client_secret.json", FileMode.Open, FileAccess.Read))        {            String FolderPath = @"D:\";            String FilePath = Path.Combine(FolderPath, "DriveServiceCredentials.json");            credential = GoogleWebAuthorizationBroker.AuthorizeAsync(                GoogleClientSecrets.Load(stream).Secrets,                Scopes,                "user",                CancellationToken.None,                new FileDataStore(FilePath, true)).Result;        }        //create Drive API service.        DriveService service = new DriveService(new BaseClientService.Initializer()        {            HttpClientInitializer = credential,            ApplicationName = "GoogleDriveRestAPI-v3",        });        return service;    }    //get all files from Google Drive.    public static List<GoogleDriveFiles> GetDriveFiles()    {        DriveService service = GetService();        // define parameters of request.        FilesResource.ListRequest FileListRequest = service.Files.List();        //listRequest.PageSize = 10;        //listRequest.PageToken = 10;        FileListRequest.Fields = "nextPageToken, files(id, name, size, version, createdTime)";        //get file list.        IList<Google.Apis.Drive.v3.Data.File> files = FileListRequest.Execute().Files;        List<GoogleDriveFiles> FileList = new List<GoogleDriveFiles>();        if (files != null && files.Count > 0)        {            foreach (var file in files)            {                GoogleDriveFiles File = new GoogleDriveFiles                {                    Id = file.Id,                    Name = file.Name,                    Size = file.Size,                    Version = file.Version,                    CreatedTime = file.CreatedTime                };                FileList.Add(File);            }        }        return FileList;    }    //file Upload to the Google Drive.    public static void FileUpload(HttpPostedFileBase file)    {        if (file != null && file.ContentLength > 0)        {            DriveService service = GetService();            string path = Path.Combine(HttpContext.Current.Server.MapPath("~/GoogleDriveFiles"),            Path.GetFileName(file.FileName));            file.SaveAs(path);            var FileMetaData = new Google.Apis.Drive.v3.Data.File();            FileMetaData.Name = Path.GetFileName(file.FileName);            FileMetaData.MimeType = MimeMapping.GetMimeMapping(path);            FilesResource.CreateMediaUpload request;            using (var stream = new System.IO.FileStream(path, System.IO.FileMode.Open))            {                request = service.Files.Create(FileMetaData, stream, FileMetaData.MimeType);                request.Fields = "id";                request.Upload();            }        }    }    //Download file from Google Drive by fileId.    public static string DownloadGoogleFile(string fileId)    {        DriveService service = GetService();        string FolderPath = System.Web.HttpContext.Current.Server.MapPath("/GoogleDriveFiles/");        FilesResource.GetRequest request = service.Files.Get(fileId);        string FileName = request.Execute().Name;        string FilePath = System.IO.Path.Combine(FolderPath, FileName);        MemoryStream stream1 = new MemoryStream();        // Add a handler which will be notified on progress changes.        // It will notify on each chunk download and when the        // download is completed or failed.        request.MediaDownloader.ProgressChanged += (Google.Apis.Download.IDownloadProgress progress) =>        {            switch (progress.Status)            {                case DownloadStatus.Downloading:                    {                        Console.WriteLine(progress.BytesDownloaded);                        break;                    }                case DownloadStatus.Completed:                    {                        Console.WriteLine("Download complete.");                        SaveStream(stream1, FilePath);                        break;                    }                case DownloadStatus.Failed:                    {                        Console.WriteLine("Download failed.");                        break;                    }            }        };        request.Download(stream1);        return FilePath;    }    // file save to server path    private static void SaveStream(MemoryStream stream, string FilePath)    {        using (System.IO.FileStream file = new FileStream(FilePath, FileMode.Create, FileAccess.ReadWrite))        {            stream.WriteTo(file);        }    }    //Delete file from the Google drive    public static void DeleteFile(GoogleDriveFiles files)    {        DriveService service = GetService();        try        {            // Initial validation.            if (service == null)                throw new ArgumentNullException("service");            if (files == null)                throw new ArgumentNullException(files.Id);            // Make the request.            service.Files.Delete(files.Id).Execute();        }        catch (Exception ex)        {            throw new Exception("Request Files.Delete failed.", ex);        }    }}

}

I would want to know how I can implement like md5 hash for this so that i can compare for any duplicated hash and prevent user from uploading.