Teams High-Level Design

This document provides a high-level description of Keybase teams, specifying applications, team roles and team structure.

Teams and Subteams

A root team is a top-level identifier in the Keybase namespace, which obeys the same parsing rules as Keybase usernames. So valid root teams include nike, google, or friends_of_max. These names are visible to the whole world, so if you create the team lets_fire_bob, the whole world will see it, they just won't be able to get any details about who the members are unless they are themselves team members.

Subteams are nested below root teams. So nike.hr, nike.hr.interns, and nike.hr.interns.volleyball are all valid subteams. The very existence of subteams are hidden from all who aren't members of the subteam. Thus, if you wanted to create the team lets_fire_bob.just_kidding_fire_bruce, then Bruce would have no way of knowing his number is up.

As we will see, every team and subteam has its own signature chain that's inserted directly into the Keybase global tree. But subteams exist in this tree under pseudonyms, pointed to by their parent teams. So they can remain private, but the team members can be certain that the Keybase servers aren't equivocating about the team definitions.

Applications

Chat and KBFS are the two applications that we initially support with Keybase teams. In both cases, teams are a mutable and uniquely identified by name, without fear of a malicious server remapping a teams.

For chat, every team like nike.hr.interns.volleyball, will have private chats, with multiple channels, and every member of the team, regardless of their role, will have full access to the chats.

For KBFS, team shares will be available under paths such as /keybse/team/nike and /keybase/team/nike.hr.interns.volleyball. Those with write permissions (or more) will be able to read and write the team, while those with only read permissions will lack write privileges.

Right now, Keybase does not support shares across teams, like /keybase/team/nike,adidas, since so doing would reveal nike's membership to adidas, and vice versa.

Team Roles

  • A team is a group of keybase users, consisting of: admins, owners, implicit admins, readers and writers.
  • A reader can read the KBFS folders for a team, and he can both read and write a team's chat.
  • A writer has all of the permissions of a reader, but can also write to the team's KBFS resources.
  • An admin can add or remove admins, readers, and writers to the team, and establish a subteam for the team. An admin can additionally deactivate a team as long as it's not a root team.
  • An implicit admin is one who is an admin of a parent subteam, but not this subteam
  • All explicit admins have read/write access to their teams, and get full access to server-gated keys, which in turn allow access to KBFS and chat data.
  • An implicit admin of a subteam who hasn't been explicitly added to the subteam does not get access to server-gated keys for that team, and therefore does not get access to KBFS and chat data.
  • Thus, a subteam can avoid dangerous situations in which all of its members have lost their access to data.
  • But Keybase can still enforce, for instance, that a sysadmin for Campbell Soup Corp. can't download the C*O team documents.
  • An owner is an admin for root team who additionally has the power to delete the team.

The cryptographic mechanism here is that for any shared secret team key the team needs (for Chat or KBFS or Saltpack), the ultimate key used is an XOR of: (1) the shared key that is encrypted for all user's Per-User Keys; and (2) a server-stored key-half that is only distributed if the ACLs permit it. This setup gives the server the ability to break the user's attempt to decrypt their KBFS or Chat, but it has that ability anyways by just corrupting all of the ciphertexts.

Access Matrix

The above properties are summarized in the following access matrix:

role owner admin implicit admin writer reader
add/remove owner 1 0 0 0 0
add/remove readers,writers,admins 1 1 1 0 0
write TLF metadata 1 1 1 1 0
read TLF metadata 1 1 1 1 1
ask TLF metadata to be rekeyed 1 1 1 1 1
read KBFS files 1 1 0.5 1 1 implicit admin blocked by access control
write KBFS files 1 1 0.5 1 0 implicit admin blocked by access control
read chat 1 1 0.5 1 1 implicit admin blocked by access control
write chat 1 1 0.5 1 1 implicit admin blocked by access control
make chat channels 1 1 1 1 0.5 readers blocked by access control
create subteam of current team 1 1 1 0 0
can delete the team if is root team 1 0 N/A 0 0 root teams (e.g., nike) don't have implicit admins
can delete the team if is a subteam N/A 1 1 0 0 a subteam (e.g., nike.usa) can't have an owner

Legend

Access Permitted (✓)
Access withheld via server-trusted Access Control (👮)
Access cryptographically denied (✗)