Abstract. How can a RFID (Radio Frequency Identification Devices) system prove that two or more RFID tags are in the same location? Previous researchers have proposed yoking-proof and grouping-proof techniques to address this problem -and when these turned out to be vulnerable to replay attacks, a new existence-proof technique was proposed. We critique this class of existence-proofs and show it has three problems: (a) a race condition when multiple readers are present; (b) a race condition when multiple tags are present; and (c) a problem determining the number of tags. We present two new proof techniques, a secure timestamp proof (secTS-proof) and a timestampchaining proof (chaining-proof) that avoid replay attacks and solve problems in previously proposed techniques.

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An experimental investigation is conducted into the indoor formaldehyde decomposition performance of an atmospheric plasma reactor with an airflow rate of 200 L/s, discharge power of 50 W, and operating voltage of 8.5 kV, utilizing a sensor network. It is shown that, given an initial formaldehyde concentration of ∼0.2 ppm, the reactor removes 15∼80% of the formaldehyde at a height of 107 cm and 20∼73% at a height of 180 cm after 5.5 hours. Moreover, it is shown that, in decomposing the formaldehyde, the reaction process does not generate O 3 . Finally, it is shown that the reduction in the formaldehyde concentration is particularly significant near the outlet of the plasma reactor and between the reactor and the door.

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