HPKE support for AAD

[BrianSipos]

Currently the HPKE Suite API has encrypt and decrypt argument "info" to provide KDF extra info, but does not have argument "aad" to provide AEAD input of AAD.

Without this, I am not able to validate examples from RFC 9180 which do use AAD.

[alex]

Do you have an actual use case, or is this purely for verifying RFC examples?

[BrianSipos]

This came about when trying to implement COSE HPKE draft. I have a question into the authors about whether or not this is necessary given the guidance from RFC 9180 that I understand this API is currently following.

I will relay any response from the authors and/or close this ticket if it becomes unnecessary.

[BrianSipos]

So it appears that a replacement internet draft draft-ietf-hpke-hpke will be updating the HPKE API and removing that limitation on inputs recommended in RFC 9180.

I don't believe that the mechanism is different, and it would have backward compatibility if a new optional "aad" argument were added with a default behavior that matches the current implementation. Please let me know if I can help with implementation or testing of this potential update to the HPKE API.