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26 lines
1.6 KiB
Markdown
26 lines
1.6 KiB
Markdown
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# Gadgets
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When implementing a circuit, we could use the features of the cores we've selected directly
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via the chip. Typically, though, we will use them via ***gadgets***. This indirection is
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useful because, for reasons of efficiency and limitations imposed by UPA, the core interfaces
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will often be dependent on low-level implementation details. The gadget interface can provide
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a more convenient and stable API that abstracts away from extraneous detail.
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For example, consider a hash function such as SHA-256. The interface of a core supporting
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SHA-256 might be dependent on internals of the hash function design such as the separation
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between message schedule and compression function. The corresponding gadget interface can
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provide a more convenient and familiar `update`/`finalize` API, and can also handle parts
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of the hash function that do not need core support, such as padding. This is similar to how
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[accelerated](https://software.intel.com/content/www/us/en/develop/articles/intel-sha-extensions.html)
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[instructions](https://developer.arm.com/documentation/ddi0514/g/introduction/about-the-cortex-a57-processor-cryptography-engine)
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for cryptographic primitives on CPUs are typically accessed via software libraries, rather
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than directly.
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Gadgets can also provide modular and reusable abstractions for circuit programming
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at a higher level, similar to their use in libraries such as
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[libsnark](https://github.com/christianlundkvist/libsnark-tutorial) and
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[bellman](https://electriccoin.co/blog/bellman-zksnarks-in-rust/). As well as abstracting
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*functions*, they can also abstract *types*, such as elliptic curve points or integers of
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specific sizes.
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