[tor-relays] Proposal: Restrict ContactInfo to Mandatory Email Address

Georg Koppen gk at torproject.org
Sat Oct 21 15:54:37 UTC 2023

Hello everyone!

As indicated in our bug tracker a while ago[1] we have some strong 
incentives to redo our ContactInfo field. I've collected all the 
different use cases and combined them in a single proposal, discussing 
some potential concerns and future work we could get built upon it. The 
work is tracked on Gitlab as well[2] feel free to provide feedback there 
or here on the list as a follow-up to this announcement. For your 
convenience the proposal text is included below (if you like reading the 
.md file on Gitlab, see my personal repository for the latest draft[3]).

Filename: 100-contactinfo-mandatory-email-address.md
Title: Restricting ContactInfo to Mandatory Email Address
Author: Georg Koppen
Created: 2023-10-21
Status: Open

## Overview

This document proposes to change the ContactInfo field from a free text
field to one that is only allowing an email address. Additionally,
providing such an email address will be required after this proposal is
implemented. This is a normative document.

## Motivation

Being able to reach out to and contact relay operators (bridge operators
are included in that group) is important for our day-to-day work at Tor.
While this has been brought up in the past as helpful in our fight
against malicious relays, it goes well beyond that use case and is
affecting general network health work, community-building efforts and
quickly deploying anti-censorship related security fixes among other

Tor is providing a `torrc` configuration option, `ContactInfo`, which is
supposed to contain an email address (potentially obfuscated) under
which the relay operator may be reached. However, in practise this does
not work very well for two reasons:

1. `ContactInfo` is a free-form field which allows the operator to
    include not just email addresses but essentially any kind of text
    they want. This results in a lot of overhead when trying to contact
    all operators and failures to do so because not everything added to
    `ContactInfo` is a way to actually contact operators or undoing
    `ContactInfo` obfuscation turns out to be too hard.
2. `ContactInfo` can be empty as it is not required for all operators
    and in cases where it is supposed to be required (e.g. for operators
    running more than one relay) the requirement is not enforced.

Over the years different teams at Tor developed different workarounds to
the issues mentioned above without addressing them directly. The goal of
this proposal is to make those workarounds obsolete.

## Fixing ContactInfo

As briefly mentioned in the [Overview section](#overview) the idea of
this proposal is deceptively simple: `ContactInfo` will be turned into a
field allowing just an email address, under which the operator can be
reached.  Moreover, providing such an address will be a requirement for
all operators regardless whether they run one relay or many of them, or

Why will we require an email address and not, say, a domain set up
somewhere or an account on our forum instead? Firstly, a lot of those
other potential options require a valid email address themselves in the
first place and would therefore just raise the costs for relay
operators. Secondly, email still scales way better than other
alternatives allowing us to reach more people in less time. And,
thirdly, email addresses are required anyway in other network related
infrastructure parts, e.g. the RIPE database for IP address space
allocation comes to mind or abuse contacts for dealing with potentially
malicious Tor traffic/Tor users.

Even though this proposal will not lay out the envisioned changes at a
technical level (for that to happen we'll need a corresponding
[tor-spec] proposal later on) there are a number of details to consider
mainly stemming from the status quo existing for years and the
accumulated usage patterns of the `ContactInfo` field "in the wild".

The remainder of this proposal will be devoted to explain those details
and address potential concerns related to them.

## Implementation

The C-Tor codebase is in maintenance mode and not accepting any new
features anymore (with a very narrow set of exceptions). We therefore
plan to have this change included solely in the upcoming Arti relay
work. Note: while we'll be using `ContactInfo` throughout this proposal
it does no mean that the respective configuration option for Arti relay
will be the same. It could just be [`contact`] or something else. The
important point is that this proposal applies to whatever is providing
the argument for the "contact" keyword in the server descriptor then.

Requiring a syntactically correct email address in an Arti relay
configuration option is necessary but not sufficient for our purposes.
Otherwise `ContactInfo` values like `nobody at example.com`, which is used
by some relays and bridges in the Tor network at the time of writing
this proposal, would be acceptable.  However, in that case there would
be no way to get into contact with respective relay operators. We intend
to solve that problem by deploying an email verification service: relays
without a verified `ContactInfo` value won't be allowed on the network.

## Concerns

There are some concerns related to this proposal which we should discuss
and address where needed. The following sections will outline them and
explain why (and how) we think they are non-issues or can be mitigated.

### Backward compatibility and breakage of external tooling

What do we do with `ContactInfo` strings that are not email addresses
already? The main goal should be to make the transitioning process to
the new `ContactInfo` string as smooth and easy for relay operators as
possible. The good news is that we plan to have a transitioning tool for
the overall change of C-Tor relays to Arti relays anyway and having the
`ContactInfo` change be part of that should help. Running an awareness
campaign and providing up-to-date documentation to reach operators that
need to fix (or even set up) their `ContactInfo` manually should further
minimize the risk of losing relays in the network and volunteers running
them to begin with.

However, even if it were possible to extract an email address from the
C-Tor relay configuration of any C-Tor relay or bridge without manual
intervention by the operator there is another problem to consider: there
is often additional information available in current `ContactInfo`
strings, which sometimes external tools got built upon. One well-known
example for that is [`OrNetStats`] which aims at displaying statistics
related to relays and bridges in the Tor network.  One important piece
of it is grouping the displayed information around so-called
Authenticated Relay Operator IDs (AROIs) were possible, which got
developed in the [ContactInfo Information Sharing Specification] \(CIISS)
and is making use of overloading the `ContactInfo` field with additional
information besides an email address. While we can't avoid breaking
tools when evolving the `ContactInfo` semantics we can provide ways for
those tools to get adapted to the new reality. For that we propose to
create an additional configuration option that includes the non-email
address information in the `ContactInfo` field and is made public in
extra-info descriptors. Even though we believe validated email addresses
as proposed in this proposal together with the planned
[happy families proposal] and [proposal 347] provide similar benefits as
the AROI mechanism, and hence make it superfluous, if someone would
still like to center their relays statistics around AROIs they could do
so by extracting the necessary information from extra-info descriptors
after this proposal got implemented.

### Spam

Exposing an email address without obfuscation in the `ContactInfo` field
is a potential spam risk which is why some operators have resorted to
obfuscating it, often in very creative ways. However, we do think that
those efforts are not effective if we want to retain a way of being able
to reach operators by email.  Moreover, our own and others' experience
of running relays and providing an unobfuscated email address as
`ContactInfo` shows that spam right now is actually not an issue. That
might change in the future, though, which is why we strongly recommend
to use a dedicated and long-term email address in the `ContactInfo`
field. The long-term part is particularly important, as this proposal
turns that email address into a validated relay operator ID, which is
valuable for building trust over the longer run.

## Impact on relay operators and the growth of trust in the Tor network

As can be seen in the previous sections, the proposed changes in this
document can come with a cost for relay operators. However, we do not
expect them to have a lasting impact on our relay operator community and
the health of the network as those changes are mainly accompanied by a
one-time transition cost that puts a burden on our current relay
operators. And that one-time cost we try to keep as low as possible.
Additionally, we might lose or alienate some of our current and
potential new operators, as they might not want to provide any
(verifiable) email address at all as a requirement for running relays,
but rather prefer participation anonymously. However, in order to fight
malicious relays we need to strengthen our community and get to build
connections and contacts with each other, which is hard if there is no
way to get into contact to begin with. As outlined at the begin of this
document, a lack of contact information makes other day-to-day work at
Tor hard or impossible as well. Thus, overall we believe providing a
working email address when running relays is a small cost compared to
the improvements of the health of our network and the safety of our

There is another benefit which comes with this proposal: the validated
email address can essentially work as a relay operator ID (similar to
the above mentioned AROI). While we do deal with single relays or
families of them when we are trying to determine whether they pose a
danger to our users, what we are ultimately aiming at is the operator
behind them. Having something like a relay operator ID does help with
that part. But there is more: it allows us to think better about trust
on the Tor network and how we might be able to implement ideas like
"operator X is only allowed to run Y% of the Tor network" or "unknown
operators are only allowed to run Z% of Tor's network capacity", to name
just two. There are a number of proposals both [trust][torspec 103]
[related][relay-search 40001] and [not trust-related][team 220] that
would benefit from having relay operator IDs available.

## Acknowledgements

Big thanks go to @gus and @ahf for discussions and feedback around this
proposal idea, which improved this document considerably.

[tor-spec]: https://gitlab.torproject.org/tpo/core/torspec
[`OrNetStats`]: https://nusenu.github.io/OrNetStats/
[ContactInfo Information Sharing Specification]: 
[happy families proposal]: 
[proposal 347]: 
[torspec 103]: https://gitlab.torproject.org/tpo/core/torspec/-/issues/103
[relay-search 40001]: 
[team 220]: 


[1] https://gitlab.torproject.org/tpo/core/arti/-/issues/870
[2] https://gitlab.torproject.org/tpo/community/relays/-/issues/71
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