OSCORE

OSCORE, or Object Security for Constrained RESTful Environments, is an end-to-end security protocol for CoAP communications in constrained devices and networks. It provides confidentiality, integrity, and replay protection at the application layer and can operate independently of transport-layer security, making it suitable for constrained IoT deployments.

The protocol leverages COSE (CBOR Object Signing and Encryption) to encrypt and authenticate CoAP messages. It uses a security context derived from a master secret and a master salt shared by the communicating parties. Each message is protected with a content encryption key and a per-message nonce derived from a partial IV, providing freshness and preventing replay. Keys and identifiers (such as a recipient key ID) enable the appropriate recipient to decrypt and verify messages.

OSCORE supports end-to-end operation between a client and a resource server and can also be used with group security for multicast or many-to-one scenarios through an extension sometimes referred to as Group OSCORE. The security context remains independent of any intermediary proxies, which may forward messages without decrypting them, preserving end-to-end security across the network path.

In practice, OSCORE can run on top of CoAP over UDP and optionally alongside DTLS, offering interoperability with existing transport security while delivering application-layer security benefits. It is defined in RFC 8613 and relies on the COSE family of standards, such as RFC 8152, for algorithms and structure.

Applications include industrial IoT, smart homes, and other constrained networks where low overhead and robust end-to-end security are essential. OSCORE is widely implemented in constrained-device stacks and continues to influence secure CoAP deployments.