[BitTorrent] Back to Merkle Hash Trees...

Elliott Mitchell ehem at m5p.com
Sun Feb 6 21:26:42 EST 2005


>From: Olaf van der Spek <OvdSpek at LIACS.NL>
> Elliott Mitchell wrote:
> > aids cryptanalysis. As lower levels (TCP) will take care of errors, why
> > add redundancy at the application layer?
> 
> Maybe because the TCP checksum isn't (very) strong.

It is more than strong enough to fulfill its intended purpose. Mainly
guarding against errors due to line noise and other accidental errors
during packet handling.

The TCP checksum is sufficiently strong that if you get a packet where
the checksum verifies and yet has data different in any way from what the
other end sent, you can say beyond a reasonable doubt that it was caused
by deliberate action.

Note protocols like FTP which send large binary files across the Internet
without any additional checksums at all. Yet FTP works with very high
reliability. Sites publish MD5 checksums in an attempt to thwart
modification by attackers, not because there is even the slightest
concern of FTP/TCP failing.


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