[BitTorrent] file corruptions (was: BT2 & hash trees)

Gregorio Roper gregorio at gmx.li
Thu Jul 22 06:44:12 EDT 2004


> TCP is an old protocol, but an adequate one. TCP guarentees reliable
> transmission, this includes error-free. As a result the *only* way you're
> going to have a corrupt block is a software/hardware failure on the
> remote end, or enemy action.
> 
> In the case of a software/hardware failure it is unlikely they'll be able
> to compute checksums correctly and I'd be surprised that you got anything
> out of them (have to be a really subtle failure to manage to send things,
> and not get caught somewhere). In a case like this I suppose you /might/
> manage to only damage a portion of a block.
> 
> Enemy action is far more likely to produce failures that don't get caught
> in the network stack. In a case like this is enemy going to bother only
> damaging 1KB and send the other 15KB to you intact? Why not send as much
> corrupt data as possible, and cause the most damage possible? In this
> case it is *highly* unlikely that *any* of the data this peer has sent to
> you is valid; so why bother verifying 1KB sub-blocks when almost
> certainly the *entire* 16KB (or 32KB with some clients) block that was
> sent is bad?

Actually most file corruptions are caused by sloppy programming. In a 
multi-vendor environment the occasional failure of one vendor is not fatal, so 
it is likely to go unnoticed for a long while (aka lessons learned from Gnutella 
I to X). Even worse, p2p clients are very often created by notorious hackers who 
do not believe in unit tests or comments.

An attacker trying disrupt the BT network would not upload corrupt ranges, he 
would simply take down the trackers.

mfg
gregorio


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