Once there are constant or infrequently changed bits (COIBs) in two adjacent input messages of SHA-2, the switching power of input messages data registers (IMD-REGs) used for COIBs will disappear. Meanwhile, when full pipeline SHA-2 is applied in a certain application scenario where the IMD-REGs used for COIBs can be removed, more area of full pipeline SHA-2 can be saved as the proportion of IMD-REGs in message word registers increases. This paper proposes a new message expansion structure for full pipeline SHA-2 to increase the proportion of IMD-REGs. By inserting two expanders in last part of expansion structure pipeline stages and rescheduling the expander, the consumption rate of input messages will be decreased and the proportion of IMD-REGs will be increased. Compared with normal message expansion structure, the ratio of IMD-REGs to total message word registers in the proposed structure is increased from 15.1% to 41.6% for full pipeline SHA256, and 11.2% to 32.4% for full pipeline SHA512. When COIBs exists in adjacent input messages, the power and area advantages of proposed new message expansion structure have been demonstrated by FPGA and ASIC implementations.

By using metal blocks as the protective coating, placing the sensitive signals in last but second metal (LSM), integrating a low-cost one-time programming (OTP) cell in each PUF unit, the proposed switched-capacitor (SC) PUF can both provide sensitive anti-invasive-attack protective coating and stable key for the security chip. Moreover, the circuit parameters and the layout implementation of the SC PUF unit are all compatible with other digital standard cells, which greatly facilitates the integration of SC PUF unit in the security chip by using digital design flow when its function, timing, power, and layout views are characterized using commercial timing and layout extraction tools. The anti-invasive-attack ability, stability, and digital design flow compatibility of the proposed SC PUF standard cell are verified in a security chip by using a standard 0.18- μm CMOS process. The measured bit error rate, bias, average intra-die HD, and average inter-die HD of output keys after OTP is-4, 46.72%, 0%, and 50.38% respectively. Finally, the failed probing and destruction attack attempts to the coating also verify the invasive-attack-resistant property of the proposed SC PUF standard cell. With the help of SC PUF standard cell, the whole security chip can easily obtain stable keys and sensitive anti-invasive-attack ability by using digital design flow.