SimpleX-Chat/docs/rfcs/2024-02-28-pq-integration.md

PQ integration in chat

Problem

• Group size not known when joining
• Communicate intent and current state of each conversation

Solution

Group size not known when joining

• Add to XGrpInv GroupInvitation
  • pros: easy
  • cons: size can change before joining, but can ignore as it's still a good estimate

or

• Send before introductions

  • new protocol message
    • XGrpIntro :: GrpIntro -> ChatMsgEvent 'Json -- (GrpIntro is a box type with Int, for possible extension)
  • or put into XGrpInfo
    • XGrpInfo :: GroupProfile -> GroupStats -> ChatMsgEvent 'Json -- GroupData?
    • can update profile between invitation if it happened before joining
    • can later add logic to "verify" stats?
    • may be over-complicated until since there "supposed" use cases are out-of-scope / not planned / not known

• What should be default if it's not known? (e.g. admin has older version)

  • On -> then off when member count reaches 20?

Communicate intent and current state of each conversation

• Current state items

  • RCEPQEnabled (see #3845) both for direct conversation and per member (regular event items, merged in UI)
  • created when PQ changes for contact/member (e.g. received from agent on MsgMeta / SENT)
  • experimental toggle is planned: it doesn't affect contacts/members with already enabled PQ
    • contact enabled PQ always overrides toggle (can't downgrade)
    • member enabled PQ also overrides, but can downgrade if group size increases past 20

• New items communicating state of e2e encryption in conversation

  • should be well pronounced in UI, not merged
  • should always say that conversation is e2e encrypted
  • in direct chats:
    • reflect actual state of PQ at the time of creation
    • created during connection handshake when receiving first info about PQ in MsgMeta / some other event (TBC agent api)
    • will not update if state changes (e.g. upgrades), as toggle is planned to be removed, PQ can't be downgraded, all will support soon
    • flag in contacts table "e2e_info_created" to only create it once?
    • should create for legacy contacts or not?
  • in groups:
    • reflect intent (should say "PQ will be used for members who support") based on number of members (see above) + toggle
    • created at the same time as feature items? race with history may be possible, but we don't observe it? need to double check or ignore
    • if based on XGrpInv GroupInvitation (first option above), can create item even before joining
    • also will not update (as conversation progresses and it will scroll far up anyway) even if group size changes and it's disabled
    • flag in groups table "e2e_info_created" to only create it once? and state is only reflected by RCEPQEnabled items?
    • or create new such item if group size increases and PQ is off / decreases and PQ is on?
    • "large group" thresholds have to different for group size increasing (e.g. 20) and decreases (e.g. 15), to avoid constant switching on the border.

• Example texts for "e2e encryption info" chat items:

  • for direct conversations:
    • with PQ (and also forward a couple releases when more clients have upgraded):

      Messages in this conversation are end-to-end encrypted.
      Post-quantum encryption is enabled.
      

    • no PQ (experimental toggle disabled):

      -//- (e2ee)
      Post-quantum encryption is not enabled. [Also possibly:] Enabling post-quantum encryption in experimental settings will enable it in this conversation if your contact supports it.
      

    • no PQ (experimental toggle enabled):

      -//-
      Post-quantum encryption will be enabled when your contact upgrades.
      

      "upgrades" / "supports it" / "starts to support it"
    • can be of different color, but seems unnecessary
    • created once at the start of conversation
    • created once for old contacts when PQ is enabled?
  • for groups:
    • with PQ (small group; toggle enabled or later, as above):

      -//-
      Post-quantum encryption will be enabled for members who support it.
      

      can remove qualification later when most clients have upgraded
    • no PQ (large group):

      -//-
      Post-quantum encryption is not enabled (group is too large).
      

    • created each time group changes between small/large, or once?
    • created for old groups when experimental toggle is first turned on, and first message is received?

• Save PQ encryption on chat items (messages)?

  • in meta for direct + group rcv
  • in group_snd_item_statuses for group snd?
  • display in chat item details (info)
  • may be overkill if aggressive upgrade strategy is planned