**Session Date/Time:** 21 Jul 2025 15:00

# cose

## Summary
The COSE working group meeting covered several active drafts, including Merkel tree proofs, the T-SATS-T header parameter, hash envelope, BLSki representation, Sphinx Plus, and Falcon. Discussions focused on the status of these drafts and potential future directions. A significant portion of the meeting was dedicated to a presentation on HPKE, including addressing feedback from the working group last call, and a discussion ensued around context information and the inclusion of COSE Mac. Additional presentations were on C-Bore encoded X509, ASCON, and split signing algorithms.

## Key Discussion Points

*   **Merkel Tree Proofs:** In IESG evaluation, telechat scheduled.
*   **T-SATS-T Header Parameter:** Publication requested recently after rechartering, but it may need a new IETF last call.
*   **Hash Envelope:** Shepard write up is done, a new version from the authors is needed.
*   **BLSki Representation:** Updated to reference the current BBS signatures draft.
*   **Sphinx Plus and Falcon:** Actively seeking new editors. Polls were conducted to gauge interest in continuing work on these drafts.
*   **HPKE:** Extensive discussion regarding the context information structure. Debate ensued regarding the need for COSE Mac and associated use cases.
*   **C-Bore Encoded X509:**  Working group last call ended. Discussions about request template, and comments about certificate chains, certificate hash and in a certificate type.
*   **ASCON for COSE:** A new proposal to add ASCON as an AAD algorithm to COSE was presented. Advantages in energy efficiency and throughput were highlighted.
*   **Split Signing Algorithms:** Discussed motivating use cases, potential problems with RSA and the addition of a cosi sign args structure to enable passing additional context.

## Decisions and Action Items

*   **HPKE:**
    *   Move the recipient structure into the HPKE seal info parameter and prefix the context with an HPKE label. Sophie Schmidt volunteered to write a paragraph to the list explaining her suggestion.
    *   Remove COSE Mac from the HPKE draft due to lack of support.
    *   Authors will update the code, address editorial issues, and submit a new draft.
*   **Sphinx Plus:**  Continue work, Hannes will remain an editor.
*   **Falcon:**  Discontinue.
*   **C-Bore Encoded X509:** Authors will continue development, taking into consideration the recent feedback.
*   **ASCON for COSE:**  Continue working on the draft. A call for reviewers was made.

## Next Steps

*   Authors of respective drafts to address feedback received and produce updated versions.
*   Working group members to review the ASCON and Split Signing draft.
*   Discussion to continue on the mailing lists.