Re:iMessage, explained
by lxgr on Wednesday December 06, 2023 @03:26PM
(#38549024)
> iMessage uses RSA instead of Diffie-Hellman. This means there is no forward secrecy.
It's (probably, to my knowledge) true that iMessage does not have forward secrecy, but that does not follow from it using RSA:
You can have forward secrecy using RSA (e.g. by exchanging ephemeral RSA encryption keys and RSA-signing these using identity keys), and vice versa you may also not have forward secrecy with (static) Diffie-Hellman.
Ephemeral keys (and/or periodic key rotation) are what yields forward secrecy, not any particular encryption, signature, or key agreement scheme.
It's (probably, to my knowledge) true that iMessage does not have forward secrecy, but that does not follow from it using RSA:
You can have forward secrecy using RSA (e.g. by exchanging ephemeral RSA encryption keys and RSA-signing these using identity keys), and vice versa you may also not have forward secrecy with (static) Diffie-Hellman.
Ephemeral keys (and/or periodic key rotation) are what yields forward secrecy, not any particular encryption, signature, or key agreement scheme.
> * Uses Diffie Hellman + Kyber, not RSA
iMessage apparently uses ECIES in newer versions of iOS instead of RSA: https://support.apple.com/lt-lt/guide/security/sec70e68c949/...