[BitTorrent] Back to Merkle Hash Trees...

Justin Cormack justin at street-vision.com
Thu Feb 10 07:11:57 EST 2005

> On Thu, 2005-02-10 at 10:07 +0000, Justin Cormack wrote:
> > > 
> > > 
> > > Elliott Mitchell wrote:
> > > > Key property here. You can add on (feature planned for BT2), without 
> > > > changing internal node indicies.
> > > 
> > > What exactly is the planned feature?
> > > 
> > 
> > Being able to append to the data.
> > 
> > Its very useful for some applications.
> It'd be a nice property, but I don't see how live streaming data is
> compatible with BT.  The basic idea of having hashed the whole file into
> a signature kind of defeats that, doesn't it?  And the structure of the
> tree does not in any way translate into the order pieces are requested.

The idea with the reordering of the tree nodes from left to right is that
the internal hashes dont change. But yes you need to get a new root hash
as it grows, which may be problematic, although if you have a trusted 
source to get root hashes from, you can get changes too potentially.

It doesnt have to be live streaming, but at the moment if you are a TV
station you cant start to make the torrent of your TV show available until
it has finished broadcasting. Say you have a domestic box that donwloads
TV, a BT based Tivo, if you turn it on half way through a TV show and want
to record the show it cant even start until the show finishes. (There are
workarounds for this case, like just chunk the content into 10 minute blocks,
for example).

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