Oddbean

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 3. Cryptographic primitives. Curve25519 / XSalsa20 256 / Poly1305 (downgraded for the absence of PQ encryption).

We added PQ encryption in March this year: https://simplex.chat/blog/20240314-simplex-chat-v5-6-quantum-resistance-signal-double-ratchet-algorithm.html

This is done in the same way as Apple describes as PQ3 here: https://security.apple.com/blog/imessage-pq3/

it provides stronger protection than Signal design where PQ encryption only applies to the initial key exchange.

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 4. Directory service could be modified to enable a MITM attack? Yes

This is incorrect, as there is no user directory service at all (and no knowledge of even the number of users), and MITM by servers is not possible by design, even without optional security code verification (that exists to mitigate MITM by the channel you used to pass one-time invitation link, e.g. email).

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 5. Does the company log timestamps/IP addresses? Yes

This is incorrect, we never logged IP addresses and access timestamps of the users.

Further, the private message routing that is now enabled by default for all users prevents such logging by any 3rd party servers with modified code:

https://simplex.chat/blog/20240604-simplex-chat-v5.8-private-message-routing-chat-themes.html

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 6. Is the design well documented? Somewhat

The design documentation was reviewed in preparation for design security audit in July 2024 - report is about to be published.

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 Thanks to our users who highlighted these inaccuracies to us!