What is KyberPreKeyStore in signalDecryptPreKey?

[joesteen2135]

When attempting to decrypt a pre key message in Swift, it requests KyberPreKeyStore as a parameter, however I see no mention of it anywhere else, so what is it?

[jrose-signal]

Kyber keys are part of PQXDH, the protocol for establishing sessions. They work a lot like the Curve25519 keys in PreKeyStore, except that you're expected to have a "last resort key" that doesn't get thrown away after being used, in case all of the "one-time" keys have been used up.

This would be another good question for https://community.signalusers.org/.