hpke: relax seed size check in DeriveKeyPair

cloudflare / circl

CIRCL: Cloudflare Interoperable Reusable Cryptographic Library

http://blog.cloudflare.com/introducing-circl

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Open emersion opened 7 months ago

emersion commented 7 months ago

RFC 9180 section 7.1.3 says:

For a given KEM, the ikm parameter given to DeriveKeyPair() SHOULD have length at least Nsk, and SHOULD have at least Nsk bytes of entropy.

Thus, it is not a requirement for HPKE to pass a seed with a fixed size. Protocols such as MLS rely on this.