[BitTorrent] SHA-0 Broken, MD5 Rumored Broken

Elliott Mitchell ehem at m5p.com
Fri Aug 20 17:33:18 EDT 2004


>From: Martin Nilsson <yahoo at mani.user.lysator.liu.se>
> Elliott Mitchell wrote:
> > 
> > I'd tend towards adding a "hashtype" field in torrent files so hashes of
> > the same size can be distinguished; might be interesting to allow
> > multiple hash types in the same torrent file.
> 
> The only impact for BitTorrent is the possibility for malicious seeding 
> of incorrect pieces with correct hash, in a remote future. By that time 
> we will already have hash trees (and perhaps deprecated them), so the 
> issue could, and probably should, wait until then.

If there is a break and it is severe, then they could start seeding
incorrect pieces *now*. So _if_ there is a break, then BT definitely has
a problem (then again thousands of other programs do too).

Interestingly if there is a break and it only affects the strongly
collision free property of SHA-1, then you could make breakable files.
Use slack (comments fields, any chunks that will be thrown out) in your
file(s) to make a file with matching hashes. Once past a certain date
you can thoroughly kill the file.


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