IMT Atlantique IMT Atlantique IMT Atlantique This document describes CBOR Object Signing and Encryption (COSE) and JSON Object Signing and Encryption (JOSE) serializations with Ascon which is a NIST standard for lightweight cryptography. In 2019, as a part of CAESAR competition, Ascon-128 and Ascon-128a were selected as the first choice for the lightweight authenticated encryption [asconv1.2-caesar]. After, in 2023, National Institute of Standards and Technology (NIST) selected Ascon family of cryptographic algorithms to be the standard for lightweight cryptography [asconv1.2-nist]. In August 2025, NIST Special Publication 800-232 was released, defining Ascon-based lightweight cryptography standards for constrained devices [NIST.SP.800-232]. This recognition makes it particularly interesting to enable Ascon to be used with COSE and JOSE structures. This document does not define any new cryptography, only serializations of existing cryptographic systems described in [NIST.SP.800-232].