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URIs do not refer to unique files in Allmydata Tahoe

Date: 
09/13/2008
Severity: 
Low
Affected Systems: 

Known vulnerable: Tahoe v1.0 and 1.1.0
Known fixed: Tahoe v1.1.1

Summary: 

It is possible for a user to create a URI on Tahoe
that corresponds to two different files (but URIs that corresponds to two different files (but URIs
are supposed to be unique). are supposed to be unique). As a result, As a result,
an adversary might be able to publish a benign file an adversary might be able to publish a benign file
and malware under the same URI, make initially the malware and under the same URI, initially make the
benign file available to users causing the URI to be benign file available to users to be causing the URI
shared and then switch the benign file for malware shared and then switch the benign file for malware
(without changing the URI). (without changing the URI).

Details: 

Tahoe uses 3-out-of-10 ECC in its file encoding.
The most simplistic form of the attack simply The most simplistic form of the attack simply
uses (for the URI) 5 shares of the benign file uses (for the URI) 5 shares of the benign file
and 5 shares of the malicious file to construct and 5 shares of the malicious file to construct
the URI. The URI.

The check that the content matches a The check that the content matches to
hash code that is part of the URI is easily hash code that is part of the URI is easily
bypassed since doing this check happens at the bypassed since doing this happens at the check
discression of the publisher. discression of the publisher.

Impact: 
Users should not trust the uniqueness of URIs of content that they did not publish themselves. of content that they did not publish themselves. Doing so can cause data integrity issues. Doing so can cause data integrity issues.
Patches: 
None at this point.