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GetTor specification
Jacob Appelbaum
Table of Contents
0. Preface
1. Overview
2. Implementation
2.1. Reference implementation
3. SMTP transport
3.1. SMTP transport security considerations
3.2. SMTP transport privacy considerations
4. Other transports
5. Implementation suggestions
0. Preface
This document describes GetTor and how to properly implementation GetTor.
1. Overview
GetTor was created to resolve direct and indirect censorship of Tor's
software. In many countries and networks Tor's main website is blocked and
would-be Tor users are unable to download even the source code to the Tor
program. Other software hosted by the Tor Project is similarly censored. The
filtering of the possible download sites is sometimes easy to bypass by using
our TLS enabled website. In other cases the website and all of the mirrors are
entirely blocked; this is a situation where a user seems to actually need Tor
to fetch Tor. We discovered that it is feasible to use alternate transport
methods such as SMTP between a non-trusted third party or with IRC and XDCC.
2. Implementation
Any compliant GetTor implementation will implement at least a single transport
to meet the needs of a certain class of users. It should be i18n and l10n
compliant for all user facing interactions; users should be able to manually
set their language and this should serve as their preference for localization
of any software delivered. The implementation must be free software and it
should be freely available by request from the implementation that they
interface with to download any of the other software available from that
GetTor instance. Security and privacy considerations should be described on a
per transport basis.
2.1. Reference implementation
We have implemented[0] a compliant GetTor that supports SMTP as a transport.
3. SMTP transport
The SMTP transport for GetTor should allow users to send any RFC822 compliant
message in any known human language; GetTor should respond in whatever
language is detected with supplementary translations in the same email.
GetTor shall offer a list of all available software in the body of the email -
it should offer the software as a list of packages and their subsequent
descriptions.
3.1. SMTP transport security considerations
Any GetTor instance that offers SMTP as a transport should optionally
implement the checking of DKIM signatures to ensure that email is not forged.
Optionally GetTor should take an OpenPGP key from the user and encrypt the
response with a blinded message.
3.2. SMTP transport privacy considerations
Any GetTor instance that offers SMTP as a transport must at least store the
requester's address for the time that it takes to process a response. This
should not be written to any permanent storage medium; GetTor should function
without any long term storage excepting a cache of files that it will send to
any user who requests it.
GetTor may optionally collect anonymized usage statistics to better understand
how GetTor[1] is in use. This must not include any personally identifying
information about any of the requester beyond language selection.
4. Other transports
At this time no other transports have been specified. IRC XDCC is a likely
useful system as is XMPP/Jabber with the newest OTR file sharing transport.
5. Implementation suggestions
It is suggested that any compliant GetTor instance should be written in a so
called "safe" language such as Python.
[0] https://gitweb.torproject.org/gettor.git
[1] https://metrics.torproject.org/packages.html
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