Currently PFS messages are decrypted and therefore modified before being
passed to the client. This make IDs computation difficult, as we pass
the whole object to the client and expect the object be passed back once
confirmed.
This changes the behavior allowing confirmation by ID, which is passed
to the client instead of the raw object.
This is a breaking change, but status-react is already forward
compatible.
We are preparing for the release of this to general public, so a few
things have been added:
1) Add versioning for bundles, and make refresh interval configurable
2) Move files to installationID so no metadata is leaked
3) Re-key using user password db
- Skipped keys
The purpose of limiting the number of skipped keys generated is to avoid a dos
attack whereby an attacker would send a large N, forcing the device to
compute all the keys between currentN..N .
Previously the logic for handling skipped keys was:
- If in the current receiving chain there are more than maxSkip keys,
throw an error
This is problematic as in long-lived session dropped/unreceived messages starts
piling up, eventually reaching the threshold (1000 dropped/unreceived
messages).
This logic has been changed to be more inline with signals spec, and now
it is:
- If N is > currentN + maxSkip, throw an error
The purpose of limiting the number of skipped keys stored is to avoid a dos
attack whereby an attacker would force us to store a large number of
keys, filling up our storage.
Previously the logic for handling old keys was:
- Once you have maxKeep ratchet steps, delete any key from
currentRatchet - maxKeep.
This, in combination with the maxSkip implementation, capped the number of stored keys to
maxSkip * maxKeep.
The logic has been changed to:
- Keep a maximum of MaxMessageKeysPerSession
and additionally we delete any key that has a sequence number <
currentSeqNum - maxKeep
- Version
We check now the version of the bundle so that when we get a bundle from
the same installationID with a higher version, we mark the previous
bundle as expired and use the new bundle the next time a message is sent
Andrea Maria Piana