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Modern messaging protocols, including the Signal Protocol used by WhatsApp, use Diffie-Hellman key agreement for Forward Secrecy. DH requires an exchange betwee
by colmmacc 3y ago
Modern messaging protocols, including the Signal Protocol used by WhatsApp, use Diffie-Hellman key agreement for Forward Secrecy. DH requires an exchange between two active parties, who will then agree on an ephemeral session key. Ideally the session key is deleted once it is no longer being used, rendering any captured cipher texts useless.
While we could encrypt sessions keys under an escrow key that the authorities control, that's a very serious degradation of forward secrecy. If an authority's escrow key is ever compromised, then all sessions encrypted with keys escrowed are also compromised. Non-negotiated keys that are re-used are also inherently more vulnerable to cryptanalysis, so it's an invitation for trouble if any cryptographic weaknesses are found in the escrow scheme. These are technical considerations.
- nvm0n2 3y agoWhatsApp already degraded their crypto to achieve their own political ends (they restrict forwarding in order to slow down the propagation of "rumors", which in a textbook e2e crypto scheme wouldn't be possible) [1]. So "it would be weaker" isn't a good argument, they already accepted it. The other objections are all Type 1 (it would be inconvenient). [1] https://faq.whatsapp.com/1053543185312573 https://faq.whatsapp.com/1053543185312573
- andrewaylett 3y agoImpossible to enforce, maybe. Include a counter on each message, incremented by one locally if forwarded. Completely insecure against malicious clients, but the threat model doesn't feature malicious clients so it works well enough.