Filename: 285-utf-8.txt Title: Directory documents should be standardized as UTF-8 Author: Nick Mathewson Created: 13 November 2017 Status: Open
1. Summary and motivation
People frequently want to include non-ASCII text in their router descriptors. The Contact line is a favorite place to do this, but in principle the platform line would also be pretty logical.
Unfortunately, there's no specified way to encode non-ASCII in our directory documents.
Fortunately, almost everybody who does it, uses UTF-8 anyway.
As we move towards Rust support in Tor, we gain another motivation for standarding on UTF-8, since Rust's native strings strongly prefer UTF-8.
So, in this proposal, we describe a migration path to having all directory documents be fully UTF-8.
2. Proposal
First, we should have Tor relays reject ContactInfo lines (and any other lines copied directly into router descriptors) that are not UTF-8.
At the same time, we should have authorities reject any router descriptors or extrainfo documents that are not valid UTF-8. Simultaneously, we can have all Tor instances reject all non-directory-descriptor directory documents that are not UTF-8, since none should exist today.
Finally, once the authorities have updated, we should have all Tor instances reject all directory documents that are not UTF-8. (We should not take this step until the authorities have upgraded, or else the behavior of updated and non-updated clients could be distinguished.)
2.1. Hidden service descriptors' encrypted bodies
For the encrypted bodies of hidden service descriptors, we cannot reject them at the authority level, and so we need to take a slightly different approach to prevent client fingerprinting attacks.
First, we should make Tor instances start warning about any hidden service descriptors whose bodies, post-decryption, contain non-utf-8 plaintext. At the same time, we add a consensus parameter to indicate that hidden service descriptors with non-utf-8 plantexts should be rejected entirely: "reject-encrypted-non-utf-8". If that parameter is set to 1, then hidden service clients will not only warn, but reject the descriptors.
Once the vast majority of clients are running versions that support the "reject-encrypted-non-utf-8" parameter, that parameter can be set to 1.