Re: [tor-bugs] #2895 [BridgeDB]: BridgeDB assumes that cached-descriptors[.new] are in chronological order

#2895: BridgeDB assumes that cached-descriptors[.new] are in chronological order
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Reporter: karsten | Owner: isis
Type: defect | Status: closed
Priority: minor | Milestone:
Component: BridgeDB | Version:
Resolution: fixed | Keywords: bridgedb-parsers, bridgedb-0.3.0
Actual Points: | Parent ID:
Points: |
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Comment (by isis):

Replying to [comment:4 arma]:
> Replying to [comment:3 isis]:
> > to my knowledge, BridgeDB has never had `cached-descriptor*` files
>
> Hm? That's how bridgedb used to know what bridges exist -- Tonga would
export its cached-descriptor* files and bridgedb would import them.

The files currently given to BridgeDB by Tonga are: `networkstatus-
bridges`, `bridge-descriptors`, `cached-extrainfo`, and `cached-
extrainfo.new`.

> In fact, I'm a bit confused that it doesn't still have them, yet there
are extrainfo descriptors. How do you know which extrainfo descriptor
matches up to which bridge descriptor? Isn't that what the "extra-info-
digest" line in the bridge descriptor is for?

Yes, that is what it is for.

No, BridgeDB (as of #9380) doesn't currently do this, but instead chains
the verification of descriptors using the `router-signature` on the `@type
bridge-extrainfo` document. (Although, I can gladly add code to check the
descriptor digest tooâ that would be part of #9380. And that might
possibly require more resources for the parsing and hashing of the `@type
bridge-extrainfo` descriptors during the extrainfo deduplication, stage
!#6 below, since the deduplication would need to do the hashing for each
one and check that the hashes match, and I would still prefer to
additionally check the signature on the `@type bridge-extrainfo`
descriptor, so that both would need to validate before updating the Bridge
with any of the extrainfo.)

BridgeDB's verification chain for descriptors currently (as of #9380) goes
like this:

1.
[https://gitweb.torproject.org/user/isis/bridgedb.git/tree/lib/bridgedb/parse/descriptors.py?h=fix/9380-stem_r10#n70
Parse] the `@type bridge-networkstatus` documents in the `networkstatus-
bridges` file.

2. Create `Bridge`
[https://gitweb.torproject.org/user/isis/bridgedb.git/tree/lib/bridgedb/bridges.py?h=fix/9380-stem_r10#n735
class] instances for each this we parsed in step !#1. Call the
`Bridge.updateFromNetworkStatus()`
[https://gitweb.torproject.org/user/isis/bridgedb.git/tree/lib/bridgedb/bridges.py?h=fix/9380-stem_r10#n1338
method] with the corresponding networkstatus document for each Bridge.
This includes storing the
[https://gitweb.torproject.org/user/isis/bridgedb.git/tree/lib/bridgedb/bridges.py?h=fix/9380-stem_r10#n1348
descriptor digest] for each Bridge.

3.
[https://gitweb.torproject.org/user/isis/bridgedb.git/tree/lib/bridgedb/parse/descriptors.py?h=fix/9380-stem_r10#n123
Parse] the `@type bridge-server-descriptor`s found in the `bridge-
descriptors` file.

4.
[https://gitweb.torproject.org/user/isis/bridgedb.git/tree/lib/bridgedb/bridges.py?h=fix/9380-stem_r10#n1363
Update] each Bridge
[https://gitweb.torproject.org/user/isis/bridgedb.git/tree/lib/bridgedb/bridges.py?h=fix/9380-stem_r10#n881
only if the descriptor digest matches] the digested value of the `@type
bridge-server-descriptor` that was just parsed.

5.
[https://gitweb.torproject.org/user/isis/bridgedb.git/tree/lib/bridgedb/bridges.py?h=fix/9380-stem_r10#n1411
Store] the `extra-info-digest` from each `@type bridge-server-descriptor`.

6.
[https://gitweb.torproject.org/user/isis/bridgedb.git/tree/lib/bridgedb/parse/descriptors.py?h=fix/9380-stem_r10#n219
Parse] and
[https://gitweb.torproject.org/user/isis/bridgedb.git/tree/lib/bridgedb/parse/descriptors.py?h=fix/9380-stem_r10#n149
deduplicate] the `@type bridge-extrainfo` descriptors in `cached-
extrainfo` and `cached-extrainfo.new`.

7.
[https://gitweb.torproject.org/user/isis/bridgedb.git/tree/lib/bridgedb/bridges.py?h=fix/9380-stem_r10#n1413
Verify] the `router-signature` on the `@type bridge-extrainfo` descriptor
for each bridge, using the `signing-key` from the Bridge's `@type bridge-
server-descriptor`.

8.
[https://gitweb.torproject.org/user/isis/bridgedb.git/tree/lib/bridgedb/bridges.py?h=fix/9380-stem_r10#n1497
Update] the Bridge's
[https://gitweb.torproject.org/user/isis/bridgedb.git/tree/lib/bridgedb/bridges.py?h=fix/9380-stem_r10#n203
PluggableTransport class] instances.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/2895#comment:5>
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