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To: cs551@merlot.usc.edu
Subject: Re: Confusion with nonce
Date: Sun, 16 Nov 2008 20:25:18 -0800
From: Bill Cheng <william@bourbon.usc.edu>

Someone wrote:

  > What if a user tries to store the same file (identical sha1 and filename)
  > multiple times with a store command? Would they be allowed to do that
  > because the newly stored file will have a different nonce than the existing
  > copy(since the nonce is not data dependent)?

Yes.  They must be allowed to do that.  Since the nonce will
be new, it's considered a different file.  Also, the 2nd time
the file is store, the user may enter different set of keywords.

  > It seems like nonces are only
  > used for probablisitic forwarding and deleting.

A nonce is used to distinguish different versions of the
same file having the same FileName and SHA1.
--
Bill Cheng // bill.cheng@usc.edu <URL:http://merlot.usc.edu/william/usc/>




  -----Original Message-----
  From: Bill Cheng [mailto:william@bourbon.usc.edu] 
  Sent: Sunday, November 16, 2008 7:03 PM
  To: cs551@merlot.usc.edu
  Subject: Re: Confusion with nonce
  
  Someone wrote;
  
    > The spec defines nonce as:
    > A nonce can be used to distinguish different versions of the same file. 
    > (If a file with a certain SHA1 value is created by a user and, at a
    > later time, the same file with the same SHA1 value is created by the
    > same user or another user, these 2 files will have different nonces.)
    > *Therefore, we consider that file Y is a copy of file X if X and Y have
    > identical FileName, SHA1, and Nonce (everything else about X and Y are
    > assumed to be identical).*
    >
    > I am not very clear about the line in bold. Does it mean that if a node
    > sees a file with the same filename, sha1 and nonce as another file that
    > is stored in the node, it has to discard that file? Right ?
  
  Correct!
  --
  Bill Cheng // bill.cheng@usc.edu <URL:http://merlot.usc.edu/william/usc/>