In this paper, we study the problem of a Boolean function can be represented as the sum of two bent functions. This problem was recently presented by N. Tokareva when studying the number of bent functions [27]. Firstly, several classes of functions, such as quadratic Boolean functions, Maiorana-MacFarland bent functions, many partial spread functions etc, are proved to be able to be represented as the sum of two bent functions. Secondly, methods to construct such functions from low dimension ones are also introduced. N. Tokareva's main hypothesis is proved for n≤6. Moreover, two hypotheses which are equivalent to N. Tokareva's main hypothesis are presented. These hypotheses may lead to new ideas or methods to solve this problem. Finally, necessary and sufficient conditions on the problem when the sum of several bent functions is again a bent function are given.

An ultra-small (0.4 0.4 mm2) radio frequency identification (RFID) chip named µ -chip has been developed for use in a wide range of individual recognition applications. The chip is designed to be 0.06 mm thick so that it can be applied to paper and to thin paper-like media, which have been used widely in retailing to create certificates that have monetary value, as well as to token-type devices. The µ-chip has been designed and fabricated using 0.18 µm standard CMOS technology with 3-layer aluminum metallization. The chip has a 128-bit memory. The memory data is easily read by applying a 2.45 GHz microwave radio frequency identification circuit technique. The minimum operating voltage of the chip's digital circuits is 0.5 V. This chip has attached to a thin-film external antenna. The chip terminals are connected to the antenna by an anisotropic conductive film (ACF). This type of structure results in a 0.15 mm thin transponder. The maximum communication distance between the µ -chip and a reader is 300 mm at a reader power of 300 mW.