HPKE algorithm clarification

[martijnharing]

Section 8.3.1 says:
Hybrid Public Key Encryption (HPKE) may be used for encrypted responses. If HPKE is used, the alg value MUST be specified according to [[I-D.ietf-jose-hpke-encrypt].

Does this mean that when using HPKE one of the algorithms specified in ietf-jose-hpke-encrypt MUST be used and other HPKE algorithms are not allowed? Or does it mean the algorithm MUST be a HPKE JWE algorithm?

[brentzundel]

From the discussion today: The group is not sure what the normative effect of this sentence is. Some additional clarity here would be helpful in providing understanding. What changes if this line is removed? Should this be pointing to the IANA registry?

[martijnharing]

The issue with the current text is that it's not clear what exactly it means, so it's difficult to say what changes if we remove it.

If it means that you must use one of the algorithms from ietf-jose-hpke-encrypt then removing it means you can also use algorithms that are not defined in ietf-jose-hpke-encrypt.
If it means the algorithm MUST be a HPKE JWE algorithm it probably doesn't change anything because it is effectively saying "if you do hpke, you have to use an hpke algorithm."
If it means something else then it depends on what that other meaning is.

[dpostnikov]

Something like this?
Hybrid Public Key Encryption (HPKE) may be used for encrypted responses. If HPKE is used, the alg value MUST point to an HPKE algorithm.