Abstract: A constrained proxy key is used to secure communications between two devices via an intermediary device. A first proxy key is generated at a host device (key generator device) based on a shared secret key, one or more constraints on the first proxy key, and a key derivation function. At least the shared secret key and key derivation function are known to the host device an a client device (authentication device). The first proxy key is sent to a proxy device to use in authenticating communications with the client device. An authenticated message is generated by the proxy device using the first proxy key and sent to the client device. The client device locally generates a second proxy key using the key derivation function, one or more constraints, and the shared secret key for authenticating the proxy device. The proxy device is authenticated if the client device successfully accesses the authenticated message from the proxy device using the second proxy key.

Abstract: A constrained proxy key is used to secure communications between two devices via an intermediary device. A first proxy key is generated at a host device (key generator device) based on a shared secret key, one or more constraints on the first proxy key, and a key derivation function. At least the shared secret key and key derivation function are known to the host device an a client device (authentication device). The first proxy key is sent to a proxy device to use in authenticating communications with the client device. An authenticated message is generated by the proxy device using the first proxy key and sent to the client device. The client device locally generates a second proxy key using the key derivation function, one or more constraints, and the shared secret key for authenticating the proxy device. The proxy device is authenticated if the client device successfully accesses the authenticated message from the proxy device using the second proxy key.