[p2p-hackers] [connellybarnes@yahoo.com: Re: [i2p] Python filesharing Merkle hash tree magic]

[Eugen Leitl]

----- Forwarded message from "C. Barnes" <connellybarnes at yahoo.com> -----

From: "C. Barnes" <connellybarnes at yahoo.com>
Date: Thu, 12 May 2005 21:07:59 -0700 (PDT)
To: i2p at i2p.net
Subject: Re: [i2p] Python filesharing Merkle hash tree magic


I didn't consider multifile torrents.  I designed this
as a general purpose module, and didn't think too much
about BitTorrent.  But for a multifile torrent you
would need to publish the root Merkle hash for *each*
file.  This would take 20*(number of files) bytes.
Thanks for pointing that out.

Also, FYI the chunk.py module uses the bencode.py
module from the BitTorrent project.

--- closedshop <closedshop at gmx.de> wrote:
> What about multifile torrents ?
> 
> C. Barnes wrote:
> 
> >Topic: P2P filesharing ala BitTorrent.
> >
> >Presenting public domain module 'chunk.py':
> >
> >  http://oregonstate.edu/~barnesc/temp/chunk.py
> >
> >This module does some magic with Merkle hash trees.
> >It allows one to publish a 20 byte SHA-1 digest for
> >a file, and encode 'chunks' from the file with
> >minimal overhead, such that any given chunk can be
> >verified against the file's 20 byte digest.
> >Cryptographic hashing is used to verify each chunk,
> >so chunks can be transmitted in any order, and it
> is
> >impossible to save corrupt data to disk if one has
> >the correct file hash.
> >
> >One could use this module in any file sharing
> >application which divides files up into blocks.
> >
> >For example, in a BitTorrent-like project it might
> >be desirable to keep the .torrent files minimal in
> >size.  Using this module, one needs to only publish
> >a hash like
> DA39A3EE5E6B4B0D3255BFEF95601890AFD80709
> >instead of a digest of all blocks in the file.
> >
> >Pros:
> > - Smaller digest size.
> > - Can send chunks in any order.
> >
> >Cons:
> > - Each 'chunk' contains checksumming information.
> >   This overhead is less than 4% for files of size
> >   less than 1e20 bytes.
> >
> > - Connelly Barnes
> >
> >
> >
> >		
> >__________________________________ 
> >Yahoo! Mail Mobile 
> >Take Yahoo! Mail with you! Check email on your
> mobile phone. 
> >http://mobile.yahoo.com/learn/mail 
> >_______________________________________________
> >i2p mailing list
> >i2p at i2p.net
> >http://i2p.dnsalias.net/mailman/listinfo/i2p
> >
> >
> >  
> >
> 
> 


		
__________________________________ 
Yahoo! Mail Mobile 
Take Yahoo! Mail with you! Check email on your mobile phone. 
http://mobile.yahoo.com/learn/mail 
_______________________________________________
i2p mailing list
i2p at i2p.net
http://i2p.dnsalias.net/mailman/listinfo/i2p

----- End forwarded message -----