Hi all, We had a discussion in the group about reducing the size of the embedded public key in the COSE-HPKE augmented COSE_Encrypt structure.
By accident I noticed that https://datatracker.ietf.org/doc/html/rfc8152#section-13.1.1 allows the use of point compression* already. Here is what it says: y: This contains either the sign bit or the value of the y-coordinate for the EC point. When encoding the value y, the integer is converted to an octet string (as defined in [SEC1<https://datatracker.ietf.org/doc/html/rfc8152#ref-SEC1>]) and encoded as a CBOR bstr. Leading zero octets MUST be preserved. The compressed point encoding is also supported. Compute the sign bit as laid out in the Elliptic-Curve-Point-to- Octet-String Conversion function of [SEC1<https://datatracker.ietf.org/doc/html/rfc8152#ref-SEC1>]. If the sign bit is zero, then encode y as a CBOR false value; otherwise, encode y as a CBOR true value. The encoding of the infinity point is not supported. In my opinion there is no further work that needs to be done on the specification side. On the implementation side the story is a bit different. Ciao Hannes *) There has also been some confusion between the terms point compression and compact encoding. IMHO these terms are used interchangeably. IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you.
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