1. A computing device, comprising: an input bridge, which is coupled to receive a sequence of data items for use by the device in execution of a program; an output bridge; a processing core, which is coupled to receive the data items from the input bridge and execute the program so as to cause the output bridge to output a signal in response to a given data item in the sequence; and authentication logic, which is coupled to receive and authenticate the data items while the processing core executes the program, and to inhibit output of the signal by the output bridge until the given data item has been authenticated.