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.

中文翻译：

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全管道SHA-2的新消息扩展结构


一旦 SHA-2 的两个相邻输入消息中存在恒定或不经常更改的位（COIB），用于 COIB 的输入消息数据寄存器（IMD-REG）的切换能力将消失。同时，当全流水线SHA-2应用于某些可以去除用于COIB的IMD-REG的应用场景时，随着消息字寄存器中IMD-REG的比例增加，可以节省更多的全流水线SHA-2面积。本文提出了一种新的全管道SHA-2消息扩展结构，以增加IMD-REG的比例。通过在扩展结构流水线阶段的最后部分插入两个扩展器并重新调度扩展器，可以降低输入消息的消耗率并增加IMD-REG的比例。与普通消息扩展结构相比，所提出的结构中IMD-REG与总消息字寄存器的比率对于全管道SHA256从15.1％增加到41.6％，对于全管道SHA512从11.2％增加到32.4％。当相邻输入消息中存在 COIB 时，FPGA 和 ASIC 实现证明了所提出的新消息扩展结构的功耗和面积优势。