A processor comprising: an instruction processing pipeline, configured to receive a sequence of instructions for execution, said sequence comprising at least one instruction including a flow control instruction which terminates the sequence; a hash generator, configured to generate a hash associated with execution of the sequence of instructions; a memory configured to securely receive a reference signature corresponding to a hash of a verified corresponding sequence of instructions; verification logic configured to determine a correspondence between the hash and the reference signature; and authorization logic configured to selectively produce a signal, in dependence on a degree of correspondence of the hash with the reference signature.