[tahoe-dev] CRISP Advisory 2008-01
christian at grothoff.org
Sun Jul 20 23:39:07 PDT 2008
Zooko asked me to post this here (and he confirmed that this is real). Oh,
and I'm not saying that this is a big deal, just that I think you may want to
consider fixing it...
Reporter: Christian Grothoff
Known vulnerable: Tahoe v1.1 and earlier
Known fixed: none
It is possible for a user to create a URI on Tahoe
that corresponds to two different files (but URIs
are supposed to be unique). As a result,
an adversary might be able to publish a benign file
and malware under the same URI, make initially the
benign file available to users causing the URI to be
shared and then switch the benign file for malware
(without changing the URI).
Users should not trust the uniqueness of URIs
of content that they did not publish themselves.
Doing so can cause data integrity issues.
Tahoe uses 3-out-of-10 ECC in its file encoding.
The most simplistic form of the attack simply
uses (for the URI) 5 shares of the benign file
and 5 shares of the malicious file to construct
the URI. The check that the content matches a
hash code that is part of the URI is easily
bypassed since doing this check happens at the
discression of the publisher.
None at this point.
I've also put this online at: http://crisp.cs.du.edu/?q=node/88
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