  Emerging ultra-low-power tiny scale computing devices in Cyber-Physical
Systems %and Internet of Things (IoT) run on harvested energy, are
intermittently powered, have limited computational capability, and perform
sensing and actuation functions under the control of a dedicated firmware
operating without the supervisory control of an operating system. Wirelessly
updating or patching the firmware of such devices is inevitable. We consider
the challenging problem of simultaneous and secure firmware updates or patching
for a typical class of such devices -- Computational Radio Frequency
Identification (CRFID) devices. We propose Wisecr, the first secure and
simultaneous wireless code dissemination mechanism to multiple devices that
prevent malicious code injection attacks and intellectual property (IP) theft,
whilst enabling remote attestation of code installation. Importantly, Wisecr is
engineered to comply with existing ISO compliant communication protocol
standards employed by CRFID devices and systems. We comprehensively evaluate
Wisecr's overhead, demonstrate its implementation over standards-compliant
protocols, analyze its security and implement an end-to-end realization with
popular CFRID devices -- the open-source code is released on GitHub.
