Solved

Is GetHashCode for a file unique?

Posted on 2006-07-09
4
725 Views
Last Modified: 2012-05-05
I'm using the following example to get the hash code for a file.  Is this hash code unique or could there be instances of overlapping?  If it's the later (instance of overlapping) help me understand how it occurs or if it's a rarity.

        OpenFileDialog1.FileName = ""
        OpenFileDialog1.ShowDialog()

        If OpenFileDialog1.FileName = "" Then Exit Sub

        Dim File_Stream As New System.IO.StreamReader(OpenFileDialog1.FileName)
        Dim File_Hash As Integer = File_Stream.ReadToEnd().GetHashCode()

        RichTextBox1.Text = File_Hash

        File_Stream.Close()
        File_Stream = Nothing
0
Comment
Question by:IUFITS
  • 2
  • 2
4 Comments
 
LVL 45

Accepted Solution

by:
aikimark earned 500 total points
ID: 17069614
it is a rarity, but collisions can occur.  It only returns a 32-bit value, so there are only 4+ billion unique hash values.

http://msdn2.microsoft.com/en-us/library/system.string.gethashcode.aspx
0
 
LVL 3

Author Comment

by:IUFITS
ID: 17072665
Thanks for the answer.
0
 
LVL 45

Expert Comment

by:aikimark
ID: 17072769
Thanks for the points.  Glad I could help.

A much better hash alternative woulld be SHA-2/SHA160, SHA256, SHA1024.

MD5 is ok for non-sensitive applications, but NIST has put it on a "don't use for criticatl applications" list.
0
 
LVL 3

Author Comment

by:IUFITS
ID: 17072817
Very good, thanks for the additonal info!  :)  I'll keep that in mind.
0

Featured Post

Live: Real-Time Solutions, Start Here

Receive instant 1:1 support from technology experts, using our real-time conversation and whiteboard interface. Your first 5 minutes are always free.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Since .Net 2.0, Visual Basic has made it easy to create a splash screen and set it via the "Splash Screen" drop down in the Project Properties.  A splash screen set in this manner is automatically created, displayed and closed by the framework itsel…
Microsoft Reports are based on a report definition, which is an XML file that describes data and layout for the report, with a different extension. You can create a client-side report definition language (*.rdlc) file with Visual Studio, and build g…
Windows 10 is mostly good. However the one thing that annoys me is how many clicks you have to do to dial a VPN connection. You have to go to settings from the start menu, (2 clicks), Network and Internet (1 click), Click VPN (another click) then fi…
A short tutorial showing how to set up an email signature in Outlook on the Web (previously known as OWA). For free email signatures designs, visit https://www.mail-signatures.com/articles/signature-templates/?sts=6651 If you want to manage em…

808 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question