Hacker News new | ask | show | jobs
by morshu9001 141 days ago
Even if your client is asking other clients to verify, what if everyone has the same wrong key for a particular user Whatsapp has chosen to spoof?
1 comments
NoahZuniga 140 days ago
Well, surely your client knows what its own key is, and would notice that the listed key is wrong when it checks it.
link
morshu9001 140 days ago
They can also tell your client it has the correct key. Yours and the other clients are all talking to their mitm in this scenario. There's fundamentally no way to solve this without users verifying keys out-of-band.
link
NoahZuniga 140 days ago
> They can also tell your client it has the correct key.

No they can't. Key transparency cryptographically makes sure everyone gets the same result.

link
morshu9001 139 days ago
Key transparency is a public list of keys, like what CAs do. That still trusts an authority. Of course a third party could archive/republish the key list and you could trust them instead of Whatsapp, but that's what I call an out of band key verification.

These are all good measures though. It's much harder for Whatsapp to mass attack users this way.

link
NoahZuniga 138 days ago
Well, more than just that. For the published key transparency information to be trusted it has to not just be signed by WhatsApp, but also by an independent witness. In this case Cloudflare.

So for wa to do a man in the middle attack they would also need to convince Cloudflare to sign two inconsistent tree heads.

link