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signalapp / libsignal

Home to the Signal Protocol as well as other cryptographic primitives which make Signal possible.
GNU Affero General Public License v3.0
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Publishing New Prekeys #488

Closed seanieb closed 1 year ago

seanieb commented 1 year ago

What are the current best practices around uploading new Prekeys? Should the client poll the server to check if their pre-keys are nearly exhausted, once a day/hourly, on app startup or after a certain number of sessions? Or should the client wait for a server notification that they need to publish.

This was discussed here with respect to libsignal but no solution is mentioned: https://github.com/signalapp/Signal-Desktop/issues/221

Thanks!

jrose-signal commented 1 year ago

I know the iOS codebase best; here's what it does:

https://github.com/signalapp/Signal-iOS/blob/6ecb00288611f77c39f4f6edb307c986e3709d09/SignalServiceKit/src/Account/TSPreKeyManager.m#L143-L144

That is essentially "check every 12 hours" (the "shouldThrottle" flag is only used for debugging)…

https://github.com/signalapp/Signal-iOS/blob/6ecb00288611f77c39f4f6edb307c986e3709d09/SignalServiceKit/src/Account/RefreshPreKeysOperation.swift#L44-L48

…and "upload when the keys are 2/3 exhausted". There are a number of places that check gets called, not just app startup, in case the app stays resident in memory a long time, but the Signal chat server doesn't today send anything to the client to say you've run out of one-time pre-keys. It certainly could, however.

[edit: hm, not sure why those code snippet permalinks aren't rendering inline]