Many IoT use cases can benefit from group communication, where a user requests an IoT resource and this request can be handled by multiple IoT devices, each of which may respond back to the user. IoT group communication involves one-to-many requests and many-to-one responses, and this creates security challenges. In this paper, we focus on the provenance that has been received by an authorized device. We provide an effective and flexible solution for securing IoT group communication using CoAP,

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... where a CoAP client sends a request to a CoAP group and receives multiple responses by many IoT devices, acting as CoAP servers. We design a solution that allows CoAP servers to digitally sign their responses in a way that clients can verify that a response has been generated by an authorized member of the CoAP group. In order to achieve our goal, we leverage Decentralized Identifiers (DIDs) and Verifiable Credentials (VCs). In particular, we consider that each group is identified by a DID, and each group member has received a VC that allows it to participate in that group. The only information a client needs to know is the DID of the group, which is learned using DNSSEC. Our solution allows group members to rotate their signing keys, it achieves group member revocation, and it has minimal communication and computational overhead.