Re: [tor-dev] Timers in Arti?
On Tue, Jan 9, 2024 at 12:58 PM Micah Elizabeth Scott wrote: > > Ah. If you want to run an onion service you'll need to keep at least a > couple circuits open continuously for the introduction points. I'm not > sure where you would meaningfully find time to deep sleep in that > scenario. There will be ongoing obligations from the wifi/wan and tcp > stacks. You need a continuous TCP connection to the guard, and multiple > circuits that are not discarded as idle. Incoming traffic on those > circuits need to be addressed quickly or clients won't be able to connect. > > If we were really optimizing for a low power mobile onion service > platform we'd have a different way to facilitate introductions without a > continuously open set of circuits, but that would also be much more > abuse-prone. > > -beth Hm. Do you know, is it possible to make network-driven wakeup events relatively prompt? (Like, within a second or so if a TCP stream we're waiting on wakes up). If so, then onion services have a decent chance of being made to work. As for the original question about timers, it would be good to know if the variance between scheduled wakeup and actual wakeup can be bounded, or if there's any way to mark a timer as high-priority vs low-priority or something. ___ tor-dev mailing list tor-dev@lists.torproject.org https://lists.torproject.org/cgi-bin/mailman/listinfo/tor-dev
Re: [tor-dev] Timers in Arti?
Ah. If you want to run an onion service you'll need to keep at least a couple circuits open continuously for the introduction points. I'm not sure where you would meaningfully find time to deep sleep in that scenario. There will be ongoing obligations from the wifi/wan and tcp stacks. You need a continuous TCP connection to the guard, and multiple circuits that are not discarded as idle. Incoming traffic on those circuits need to be addressed quickly or clients won't be able to connect. If we were really optimizing for a low power mobile onion service platform we'd have a different way to facilitate introductions without a continuously open set of circuits, but that would also be much more abuse-prone. -beth On 1/9/24 05:19, Michael Rogers wrote: Sorry, I should have said that we're interested in keeping a hidden service running. Without that requirement, I agree we could just close the guard connection via DisableNetwork after some idle period. So the question is about keeping circuits alive, and I guess also keeping HS descriptors published and the consensus fresh, although hopefully the timing requirements for those are a bit looser due to the longer timescales involved. Cheers, Michael On 08/01/2024 21:01, Micah Elizabeth Scott wrote: A variety of timers are needed on the relay side; on the client side though, aren't you mostly limited by the requirement of keeping a TCP connection open? Really deep sleep would involve avoiding any protocol-level keepalives as well as TCP keepalives. This seems a lot like just shutting down the connection to the guard when sleeping; but of course that's got a latency penalty and it's visible to anyone who can see network activity. -beth On 1/4/24 04:48, Michael Rogers wrote: Hi, If I understand right, the C implementation of Tor has various state machines that are driven by local libevent timers as well as events from the network. For example, when building a circuit, if there hasn't been any progress for a certain amount of time then a timer fires to handle the timeout. When running Tor on Android, we need to prevent the OS from suspending so that these timers fire when they're supposed to. This uses a lot of battery, because normally the OS would spend most of its time suspended. Unlike a laptop, an Android device with its screen turned off is constantly dipping in an out of suspension, and a lot of the platform's power optimisations are aimed at batching whatever work needs to be done so that the periods of suspension can be longer. If we allowed the OS to suspend then the timers would fire with arbitrary delays, and I don't really know what impact that would have: I'd speculate that there might be connectivity problems (eg dead circuits not being detected and replaced) and/or network-visible changes in the behaviour of circuits that could affect anonymity. So I've had a longstanding but not-very-hopeful request that maybe Tor's reliance on timers could be reduced, or at least clarified, so that we could either allow the OS to suspend without breaking anything, or at least know what was likely to break. And basically I'd just like to renew that request for Arti. Could anyone give me an overview of how these local timers are handled in Arti, or any information about what's likely to happen if the timers are arbitrarily delayed? Thanks, Michael ___ tor-dev mailing list tor-dev@lists.torproject.org https://lists.torproject.org/cgi-bin/mailman/listinfo/tor-dev ___ tor-dev mailing list tor-dev@lists.torproject.org https://lists.torproject.org/cgi-bin/mailman/listinfo/tor-dev ___ tor-dev mailing list tor-dev@lists.torproject.org https://lists.torproject.org/cgi-bin/mailman/listinfo/tor-dev
Re: [tor-dev] Timers in Arti?
Sorry, I should have said that we're interested in keeping a hidden service running. Without that requirement, I agree we could just close the guard connection via DisableNetwork after some idle period. So the question is about keeping circuits alive, and I guess also keeping HS descriptors published and the consensus fresh, although hopefully the timing requirements for those are a bit looser due to the longer timescales involved. Cheers, Michael On 08/01/2024 21:01, Micah Elizabeth Scott wrote: A variety of timers are needed on the relay side; on the client side though, aren't you mostly limited by the requirement of keeping a TCP connection open? Really deep sleep would involve avoiding any protocol-level keepalives as well as TCP keepalives. This seems a lot like just shutting down the connection to the guard when sleeping; but of course that's got a latency penalty and it's visible to anyone who can see network activity. -beth On 1/4/24 04:48, Michael Rogers wrote: Hi, If I understand right, the C implementation of Tor has various state machines that are driven by local libevent timers as well as events from the network. For example, when building a circuit, if there hasn't been any progress for a certain amount of time then a timer fires to handle the timeout. When running Tor on Android, we need to prevent the OS from suspending so that these timers fire when they're supposed to. This uses a lot of battery, because normally the OS would spend most of its time suspended. Unlike a laptop, an Android device with its screen turned off is constantly dipping in an out of suspension, and a lot of the platform's power optimisations are aimed at batching whatever work needs to be done so that the periods of suspension can be longer. If we allowed the OS to suspend then the timers would fire with arbitrary delays, and I don't really know what impact that would have: I'd speculate that there might be connectivity problems (eg dead circuits not being detected and replaced) and/or network-visible changes in the behaviour of circuits that could affect anonymity. So I've had a longstanding but not-very-hopeful request that maybe Tor's reliance on timers could be reduced, or at least clarified, so that we could either allow the OS to suspend without breaking anything, or at least know what was likely to break. And basically I'd just like to renew that request for Arti. Could anyone give me an overview of how these local timers are handled in Arti, or any information about what's likely to happen if the timers are arbitrarily delayed? Thanks, Michael ___ tor-dev mailing list tor-dev@lists.torproject.org https://lists.torproject.org/cgi-bin/mailman/listinfo/tor-dev ___ tor-dev mailing list tor-dev@lists.torproject.org https://lists.torproject.org/cgi-bin/mailman/listinfo/tor-dev OpenPGP_0x11044FD19FC527CC.asc Description: OpenPGP public key OpenPGP_signature.asc Description: OpenPGP digital signature ___ tor-dev mailing list tor-dev@lists.torproject.org https://lists.torproject.org/cgi-bin/mailman/listinfo/tor-dev
