What unique construction does SHA-3 use to process message blocks?

SHA-3 utilizes a unique construction known as the sponge construction, which is central to its design and operating principles. The sponge construction involves the process of absorbing and squeezing. During the absorbing phase, the input data (message blocks) is mixed into a fixed-size state, while in the squeezing phase, the output (hash digest) is extracted from this state.

This dual-phase approach allows SHA-3 to efficiently handle varying input lengths and produce hash outputs of different sizes while maintaining a high level of security. The versatility of the sponge construction is a key reason SHA-3 can support multiple output sizes, making it adaptable for various applications.

In contrast, other hashing mechanisms like hash tree construction, chain construction, and block cipher construction follow different methodologies. Hash tree construction organizes data in a hierarchical structure, chain construction uses a sequential process making it less flexible, and block cipher construction relies on conventional block cipher techniques, which differ significantly from the absorbing and squeezing method employed by SHA-3.