Opened 4 years ago

Closed 3 years ago

#15774 closed enhancement (wontfix)

Signed Fallback Directory File

Reported by: teor Owned by:
Priority: Low Milestone: Tor: unspecified
Component: Core Tor/Tor Version: Tor: 0.2.4.7-alpha
Severity: Normal Keywords: lorax, tor-03-unspecified-201612
Cc: weasel, ioerror Actual Points:
Parent ID: Points:
Reviewer: Sponsor:

Description (last modified by teor)

See
https://lists.torproject.org/pipermail/tor-dev/2015-April/008682.html
and #15642, in which I say:

The function which loads fallback directories currently loads from a string array inside the function, so it would need to be modified to load from a signed file. I support the security benefits of signed fallback directories enough to write client code and unit tests for it, but I'm not sure how the code for the authorities would work - is the proposal to sign a section of the consensus, and output it as a separate file?

If so, we would either need to backport, and/or wait until a majority of the authorities update to tor versions with the feature. And perhaps a majority of clients as well, controlled by a consensus parameter? (Otherwise, using any entry in the file itself would allow clients to effectively be partitioned from the rest of the network by their behaviour.)

While I'm making a list, do we need to modify the existing proposal which describes fallback directories?

Is this change proposed for 0.2.7?
Or all currently supported releases?

Do we need a new configuration option to give the location of the (signed) Fallback Directories file?
How should this interact with the existing FallbackDir option?
Cumulative?

And nickm says:

I think making the file signed is a different ticket, and I don't really understand the threat model for it.

Before we make this change, we need to understand how the threat model is different from, for example:

  • a package maintainer adding their own directory
  • a package maintainer removing the signature check code
  • a package maintainer replacing all the authorities

Also:

How can a signature be verified if the client is using the fallback directories? Doesn't this mean it can't access the directories themselves? So it has to trust the keys it gets from the directories on the not-yet-verified list?

Child Tickets

Change History (5)

comment:1 Changed 4 years ago by teor

Type: defectenhancement

comment:2 Changed 4 years ago by teor

Cc: weasel ioerror added
Description: modified (diff)
Status: newneeds_information

comment:3 Changed 3 years ago by teor

Milestone: Tor: 0.2.???Tor: 0.3.???

Milestone renamed

comment:4 Changed 3 years ago by nickm

Keywords: tor-03-unspecified-201612 added
Milestone: Tor: 0.3.???Tor: unspecified

Finally admitting that 0.3.??? was a euphemism for Tor: unspecified all along.

comment:5 Changed 3 years ago by nickm

Resolution: wontfix
Severity: Normal
Status: needs_informationclosed

Closing: the only reason to do this is if we start distributing a fallback dir list in some way that doesn't accompany the tor releases.

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