January 2023 - tor-dev - lists.torproject.org

Two features that would help load-balanced bridges
by David Fifield 01 Jun '23

01 Jun '23

After the blocking of Tor in Russia in December 2022, the number of Snowflake users rapidly increased. Eventually the tor process became the limiting factor for performance, using all of one CPU core. In a thread on tor-relays, we worked out a design where we run multiple instances of tor on the same host, all with the same identity keys, in order to effectively use all the server's CPU resources. It's running on the live bridge now, and as a result the bridge's bandwidth use has roughly doubled. Design thread https://forum.torproject.net/t/tor-relays-how-to-reduce-tor-cpu-load-on-a-s… Installation instructions https://gitlab.torproject.org/tpo/anti-censorship/team/-/wikis/Survival-Gui… Two details came up that are awkward to deal with. We have workaround for them, but they could benefit from support from core tor. They are: 1. Provide a way to disable onion key rotation, or configure a custom onion key. 2. Provide a way to set a specific authentication cookie for ExtORPort SAFE_COOKIE authentication, or a new authentication type that doesn't require credentials that change whenever tor is restarted. I should mention that, apart from the load-balancing design we settled on, we have brainstormed some other options for scaling the Snowflake bridge or bridges. At this point, none of these ideas can immediately be put into practice, because there's no way to tell tor "connect to one of these bridges at random, but only one," or "connect to this bridge, but accept any of these fingerprints." https://bugs.torproject.org/tpo/anti-censorship/pluggable-transports/snowfl… # Disable onion key rotation Multiple tor instances with the same identity keys will work fine for the first 5 weeks (onion-key-rotation-days + onion-key-grace-period-days), but after that time the instances will have independently rotated their onion keys, and clients will have connection failures unless the load balancer happens to connect them to the instance whose descriptor they have cached. This post investigates what the failure looks like: https://lists.torproject.org/pipermail/tor-relays/2022-January/020238.html Examples of what could work here are a torrc option to set onion-key-rotation-days to a large value, an option to disable onion key rotation, an option to set a certain named file as the onion key. What we are doing now is a bit of a nasty hack: we create a directory named secret_onion_key.old, so that a failed replace_file causes an early exit from rotate_onion_key. https://gitweb.torproject.org/tor.git/tree/src/feature/relay/router.c?h=tor… There are a few apparently benign side effects, like tor trying to rebuild its descriptor every hour, but it's effective at stopping onion key rotation. https://lists.torproject.org/pipermail/tor-relays/2022-January/020277.html # Stable ExtORPort authentication ExtORPort (extended ORPort) is a protocol that lets a pluggable transport attach transport and client IP metadata to a connection, for metrics purposes. In order to connect to the ExtORPort, the pluggable transport needs to authenticate using a scheme like ControlPort authentication. https://gitweb.torproject.org/torspec.git/tree/proposals/217-ext-orport-aut… tor generates a secret auth cookie and stores it in a file. When the pluggable transport process is managed by tor, tor tells the pluggable transport where to find the file by setting the TOR_PT_AUTH_COOKIE_FILE environment variable. In the load-balanced configuration, the pluggable transport server (snowflake-server) is not run and managed by tor. It is an independent daemon, so it doesn't have access to TOR_PT_AUTH_COOKIE_FILE (which anyway would be a different path for every tor instance). The bigger problem is that tor regenerates the auth cookie and rewrites the file on every restart. All the tor instances have different cookies, and snowflake-server does not know which it will get through the load balancer, so it doesn't know what cookie to use. Examples of what would work here are an option to use a certain file as the auth cookie, an option to leave the auth cookie file alone if it already exists, or a new ExtORPort authentication type that can use the same credentials across multiple instances. What we're doing now is using a shim program, extor-static-cookie, which presents an ExtORPort interface with a static auth cookie for snowflake-server to authenticate with, then re-authenticates to the ExtORPort of its respective instance of tor, using that instance's auth cookie. https://lists.torproject.org/pipermail/tor-relays/2022-January/020183.html

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Simple tool for mobile remote desktops
by Micah Elizabeth Scott 24 Jan '23

24 Jan '23

Hello, This is an almost trivial utility but I hadn't seen anything quite like it so maybe other folks will find it useful: https://github.com/scanlime/onion-desktop "This is just a toy for now. I wanted to get a feel for the interactive performance of onion services, and it's perhaps sometimes useful if you'd like to share a disposable slice of your computer with a phone when they're both behind NAT. This is a very simple Docker container that runs an xfce4 desktop, novnc, and tor. It will randomly generate a new onion service URL and a VNC password, and show you a tmux with session logs on the left and a big QR code you can scan on the right." Nothing too fancy, just some shell script and Docker and a lot of Debian. The readme has a couple screenshots if you're curious. Cheers, --micah beth

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Proposal 342: Decouple hs_interval and SRV lifetime
by Nick Mathewson 24 Jan '23

24 Jan '23

``` Filename: 342-decouple-hs-interval.md Title: Decoupling hs_interval and SRV lifetime Author: Nick Mathewson Created: 9 January 2023 Status: Draft ``` # Motivation and introduction Tor uses shared random values (SRVs) in the consensus to determine positions of relays within a hash ring. Which shared random value is to be used for a given time period depends upon the time at which that shared random value became valid. But right now, the consensus voting period is closely tied to the shared random value voting cycle: and clients need to understand both of these in order to determine when a shared random value became current. This creates tight coupling between: * The voting schedule * The SRV liveness schedule * The hsdir_interval parameter that determines the length of the an HSDIR index To decouple these values, this proposal describes a forward compatible change to how Tor reports SRVs in consensuses, and how Tor decides which hash ring to use when. ## Reporting SRV timestamps In consensus documents, parties should begin to accept `shared-rand-*-value` lines with an additional argument, in the format of an IsoTimeNospace timestamp (like "1985-10-26T00:00:00"). When present, this timestamp indicates the time at which the given shared random value first became the "current" SRV. Additionally, we define a new consensus method that adds these timestamps to the consensus. We specify that, in the absence of such a timestamp, parties are to assume that the `shared-rand-current-value` SRV became "current" at the first 00:00 UTC on the UTC day of the consensus's valid-after timestamp, and that the `shard-rand-previous-value` SRV became "current" at 00:00 UTC on the previous UTC day. ## Generalizing HSDir index scheduling. Under the current HSDir design, there is one SRV for each time period, and one time period for which each SRV is in use. Decoupling `hsdir_interval` from 24 hours will require that we change this notion slightly. We therefore propose this set of generalized directory behavior rules, which should be equivalent to the current rules under current parameters. The calculation of time periods remains the same (see `rend-spec-v3.txt` section `[TIME PERIODS]`). A single SRV is associated with each time period: specifically, the SRV that was "current" at the start of the time period. There is a separate hash ring associated with each time period and its SRV. Whenever fetching an onion service descriptor, the client uses the hash ring for the time period that contains the start of the liveness interval of the current consensus. Call this the "Consensus" time period. Whenever uploading an onion service descriptor, the service uses _two or three_ hash rings: * The "consensus" time period (see above). * The immediately preceding time period, if the SRV to calculate that hash ring is available in the consensus. * The immediately following time period, if the SRV to calculate that hash ring is available in the consensus. (Under the current parameters, where `hsdir_interval = SRV_interval`, there will never be more than two possible time periods for which the service can qualify.) ## Migration We declare that, for at least the lifetime of the C tor client, we will not make any changes to the voting interval, the SRV interval, or the `hsdir_interval`. As such, we do not need to prioritize implementing these changes in the C client: we can make them in Arti only. ## Issues left unsolved There are likely other lingering issues that would come up if we try to change the voting interval. This proposal does not attempt to solve them. This proposal does not attempt to add flexibility to the SRV voting algorithm itself. Changing `hsdir_interval` would create a flag day where everybody using old and new values of `hsdir_interval` would get different hash rings. We do not try to solve that here. ## Acknowledgments Thanks to David Goulet for explaining all of this stuff to me!

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Tor Bridges and Snowflakes detection attack
by tor＠nullvoid.me 09 Jan '23

09 Jan '23

Hi, https://github.com/scriptzteam/Tor-Bridges-Collector Seems an attacker has found a way to enumerate ~300000 snowflakes and many bridges. I couldn't find any discussion about this in the archive. Thanks,

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Typo in relay metrics (circs_creared)
by Andreas Bollhalder 09 Jan '23

09 Jan '23

Hi I think, there's a typo in the file "src/feature/relay/relay_metrics.c". Shouldn't the word "circs_creared" in the line metrics_format_label("action", "circs_creared")); be read as "circs_cleared"? Andreas PS: Sorry, at the moment I've no clue what would be the correct way to send patches...

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