[CFRG] Fwd: Yet another interesting KEM combiner
Deirdre Connolly <durumcrustulum@gmail.com> Wed, 21 February 2024 20:02 UTC
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From: Deirdre Connolly <durumcrustulum@gmail.com>
Date: Wed, 21 Feb 2024 15:01:36 -0500
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Subject: [CFRG] Fwd: Yet another interesting KEM combiner
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Apple just announced their PQ3 upgrade to iMessage, with long term ML-KEM-1024 keys and occasionally ratcheting Kyber758 keys. They combine them P-256 ECDH and possibly a root key in an interesting variant of HKDF: [image: kdfskck.jpeg] https://security.apple.com/assets/files/Security_analysis_of_the_iMessage_PQ3_protocol_Stebila.pdf Based on previous literature, one would probably reach for a concatenation scheme that then is just shoved through HKDF in one go (for example in PQXDH in Signal), vs this kind of chained variant. It seems like an interesting approach and I am wondering if anyone has any more information about why one would construct it this way (the benefits vs a simpler way) Deirdre
- [CFRG] Fwd: Yet another interesting KEM combiner Deirdre Connolly