When in operation, cipher chips emit photons which can reveal important information about their operation and data. An experimental system based on single-photon counting for the detection, transmission, processing and analysis of photonic emission from CMOS semiconductor integrated circuits has been designed and constructed. Using time-correlated single-photon counting (TCSPC) technology, we have analyzed the photon emission of cipher chip AT89C52, and measured the relationship between its emission intensity and voltage. We have also analyzed in detail the relationship between the photonic emission and the operations and data processed in the chip at the instruction level. Furthermore, we have confirmed the feasibility of our TCSPC technique using an oscilloscope. Our experimental results show that cipher chip photonic emission analysis based on TCSPC technology is a relatively low cost but effective method for optical side-channel attacks, and that it poses a serious practical threat to cipher chip security.