**Session Date/Time:** 24 Jul 2023 20:00

# cose

## Summary

This COSE meeting covered several topics, including post-quantum cryptography, timestamp tokens, seaborne-encoded certificates, Merkel tree proofs, key thumbprints, type header parameters, and HPKE integration. Discussions focused on implementation details, standardization efforts, and design choices for integrating these features with COSE.

## Key Discussion Points

*   **Post-Quantum Drafts:** Discussion on dilithium, Falcon, and Sphinx Plus signing mechanisms. Focus on test vectors, implementation interoperability, and alignment with related work in LAMPS and JOSE. John raised concerns about proceeding to last call before algorithm standardization. Lawrence questioned the need for all three algorithms.
*   **Timestamp Token Header Parameter:** Discussion on whether to use a single header parameter or separate parameters for protected and unprotected header buckets based on different procedures. Mike suggested stating it belongs only in the protected header to avoid misuse.
*   **Seaborne Encoded Certificates:** Minor updates were presented, with plans to split CRL and OCSP seaborne codings into a separate draft. Discussion on parsing the container message, further amortization and registering more extensions.
*   **Signed Merkel Tree Proofs:** Updates on verifiable data structures and proof types. Emphasis on improved CDDL examples and monitoring proof type output from KT.
*   **COSE Key Thumbprint Draft:** Proposed method for calculating key thumbprint values from COSE key objects. Discussion of existing standards and a desire to implement solely within COSE objects. Brendan suggested including symmetric keys.
*   **TIP Type Header Parameter:** Adds the CYP header parameter to the COSE protected header parameter list, enabling typing the entire COSE structure. Discussion on interactions with countersigning.
*   **HPKE:** Two proposals were discussed. Proposal 1 involves each field being separately chosen from the HPKE registry, while proposal 2 advocates for complete suites being registered. It was debated which direction was less prone to error. There were issues of encoding Enc parameters. There are questions of whether the HPKE keys should be wrapped using cozy sign. There were discussions of removing certain levels of abstraction for the HPKE implementation.

## Decisions and Action Items

*   **Post-Quantum Drafts:** Mike Prorock volunteered to do the shepherd write-up.
*   **Timestamp Token Header Parameter:** Call for adoption to be initiated on the mailing list.
*   **COSE Key Thumbprint Draft:** The chairs will assess the result of the adoption call. Review is requested once the document is published as a working group draft.
*   **Signed Merkel Tree Proofs:** An adoption call on the list.
*   **HPKE:** The topic will be taken back to the list for discussion.

## Next Steps

*   Address review comments and implement changes to the respective drafts.
*   Conduct adoption calls on the mailing list for approved drafts.
*   The chairs will assess the adoption call for the COSE Key Thumbprint Draft.
*   Continue discussions on the HPKE design choices on the mailing list.