This paper describes the results of the practical measurements done to determine the path delay associated with each bit of a hardware AES FPGA implementation using a clock glitch injection tool. We illustrate how the measured path delays can constitute a characteristic fingerprint of an Intellectuel Property (IP) and can be used to detect the insertion of hardware trojans. The influence of synthesis options and inter die variations on the measurements is also studied. Compared to trojan detection schemes based on path delay characterisations already proposed in the literature, our approach does not require any additional test circuit to be inserted in the IP. Moreover our results are based on practical measurements.