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on fill server OTKs up to max/2

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so we don't remove keys for yet to be received
olm messages that claimed a key
This commit is contained in:
Bruno Windels 2021-03-09 12:33:31 +01:00
parent 0b211e8e1c
commit 8cd6a7988a
1 changed files with 36 additions and 15 deletions
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49
src/matrix/e2ee/Account.js
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@ -117,31 +117,52 @@ export class Account {
}
async generateOTKsIfNeeded(storage, log) {
// We need to keep a pool of one time public keys on the server so that
// other devices can start conversations with us. But we can only store
// a finite number of private keys in the olm Account object.
// To complicate things further then can be a delay between a device
// claiming a public one time key from the server and it sending us a
// message. We need to keep the corresponding private key locally until
// we receive the message.
// But that message might never arrive leaving us stuck with duff
// private keys clogging up our local storage.
// So we need some kind of engineering compromise to balance all of
// these factors.
// Check how many keys we can store in the Account object.
const maxOTKs = this._account.max_number_of_one_time_keys();
const limit = maxOTKs / 2;
if (this._serverOTKCount < limit) {
// TODO: cache unpublishedOTKCount, so we don't have to parse this JSON on every sync iteration
// for now, we only determine it when serverOTKCount is sufficiently low, which is should rarely be,
// and recheck
// Try to keep at most half that number on the server. This leaves the
// rest of the slots free to hold keys that have been claimed from the
// server but we haven't recevied a message for.
// If we run out of slots when generating new keys then olm will
// discard the oldest private keys first. This will eventually clean
// out stale private keys that won't receive a message.
const keyLimit = Math.floor(maxOTKs / 2);
// does the server have insufficient OTKs?
if (this._serverOTKCount < keyLimit) {
const oneTimeKeys = JSON.parse(this._account.one_time_keys());
const oneTimeKeysEntries = Object.entries(oneTimeKeys.curve25519);
const unpublishedOTKCount = oneTimeKeysEntries.length;
const totalOTKCount = this._serverOTKCount + unpublishedOTKCount;
if (totalOTKCount < limit) {
// we could in theory also generated the keys and store them in
// writeSync, but then we would have to clone the account to avoid side-effects.
await log.wrap("generate otks", log => this._updateSessionStorage(storage, sessionStore => {
const newKeyCount = maxOTKs - totalOTKCount;
// we want to end up with maxOTKs / 2 key on the server,
// so generate any on top of the remaining ones on the server and the unpublished ones
// (we have generated before but haven't uploaded yet for some reason)
// to get to that number.
const newKeyCount = keyLimit - unpublishedOTKCount - this._serverOTKCount;
if (newKeyCount > 0) {
await log.wrap("generate otks", log => {
log.set("max", maxOTKs);
log.set("server", this._serverOTKCount);
log.set("unpublished", unpublishedOTKCount);
log.set("new", newKeyCount);
log.set("limit", limit);
log.set("limit", keyLimit);
this._account.generate_one_time_keys(newKeyCount);
this._updateSessionStorage(storage, sessionStore => {
sessionStore.set(ACCOUNT_SESSION_KEY, this._account.pickle(this._pickleKey));
}));
return true;
});
});
}
// even though we didn't generate any keys, we still have some unpublished ones that should be published
return true;
}
return false;
}