Secured device, secured method, secured system, and secured apparatus

A secured device includes an interface and a processor. The interface is configured to connect to a bus, to which a host and a second device are coupled. At least the second device operates over the bus in a slave mode, and the host operates on the bus as a bus master that initiates transactions on the bus, at least on behalf of the secured device. The processor is configured to request the host to initiate, for the secured device, a transaction that accesses the second device over the bus, to monitor one or more signals on the bus, at least within a period during which the host accesses the second device over the bus in performing the requested transaction, and to identify, based on the monitored signals, whether a security violation occurred in performing the requested transaction.