diff --git a/draft-ietf-lamps-pq-composite-kem.md b/draft-ietf-lamps-pq-composite-kem.md index c98e14f..875130e 100644 --- a/draft-ietf-lamps-pq-composite-kem.md +++ b/draft-ietf-lamps-pq-composite-kem.md @@ -818,11 +818,17 @@ In the interests of simplicity and avoiding compatibility issues, implementation ## Key Usage Bits -For protocols such as X.509 [RFC5280] that specify key usage along with the public key, then the composite public key associated with a Composite ML-KEM algorithm MUST contain only a `keyEncipherment` key usage, all other key usages MUST NOT be used. -This is because the composite public key can only be used in situations -that are appropriate for both component algorithms, so even if the -classical component key supports both signing and encryption, -the post-quantum algorithms do not. +When any of the Composite ML-KEM `AlgorithmIdentifier` appears in the `SubjectPublicKeyInfo` field of an X.509 certificate [RFC5280], the key usage certificate extension MUST only contain + +~~~ +keyEncipherment +~~~ + +Composite ML-KEM keys MUST NOT be used in a "dual usage" mode because even if the +traditional component key supports both signing and encryption, +the post-quantum algorithms do not and therefore the overall composite algorithm does not. + + # Composite ML-KEM Structures