GetTor specification Jacob Appelbaum 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