[tor-dev] bridge:// URI and QR codes

[Michael Rogers]

On 20/07/2022 18:15, Nathan Freitas wrote:
> 
> 
> On Wed, Jul 20, 2022, at 8:01 AM, meskio wrote:
>> Quoting Torsten Grote (2022-07-19 14:54:01)
>>> On Monday, 18 July 2022 13:47:21 -03 meskio wrote:
>>>> What do you think of the proposal? How can we improve it?
>>>
>>> A slightly unrelated question:
>>>
>>> Was there any consideration about deanonymization attacks by giving the user a
>>> bridge controlled by the attacker? I worry that those get more likely when
>>> getting bridges via links and QR codes becomes normalized.
>>>
>>> Apart from the source IP address of the user and their Tor traffic pattern, is
>>> there anything else an attacker can learn from operating the bridge?
>>
>> At least from my side there was not consideration on this topic yet. Thank you
>> for bringing it, I think is a pretty valid concern and we should do some
>> planning on it.
>>
>> I wonder if we should only accept bridge URIs/QR codes when the user
>> clicks on
>> 'add bridges' inside the tor related app. Or will be enough to accept
>> bridge
>> URIs on any moment but communicate to the user clearly what is
>> happening and ask
>> them for confirmation. We should never change the bridge configuration
>> silently
>> from a bridge URI without any user intervention.
>>
>> I think we should add something about it to the "Recommendations to
>> implementers" on the proposal.
> 
> I believe in Orbot today we do promote the user after they scan a code or click on a bridge link. Definitely agree there should be that step.

Another thing that would be useful for this scenario would be for 
BridgeDB to publish some kind of signed record saying "the bridge with 
such-and-such a fingerprint was known to BridgeDB at such-and-such a 
time" - similar to what can already be queried via the API, but in a 
form that could be distributed offline.

If users were able to distribute these records alongside the 
corresponding bridge lines then apps might decide to treat BridgeDB 
bridges differently - for example, showing a warning if the bridge 
entered by the user was *not* signed by BridgeDB. This would provide a 
useful second layer of trust when finding bridges from sources like 
Telegram bots, where the provenance isn't always clear.

However, including these signatures in a bridge URI might make the URI 
quite long, which in turn might cause issues with scanning QR codes. So 
there might be tradeoffs here.

Cheers,
Michael
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