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31 lines
1.2 KiB
C
31 lines
1.2 KiB
C
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#ifndef PQCLEAN_SPHINCSSHAKE256256SROBUST_AVX2_HASH_STATE_H
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#define PQCLEAN_SPHINCSSHAKE256256SROBUST_AVX2_HASH_STATE_H
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/**
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* Defines the type of the hash function state.
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*
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* Don't be fooled into thinking this instance of SPHINCS+ isn't stateless!
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*
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* From Section 7.2.2 from the SPHINCS+ round-2 specification:
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*
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* Each of the instances of the tweakable hash function take PK.seed as its
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* first input, which is constant for a given key pair – and, thus, across
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* a single signature. This leads to a lot of redundant computation. To remedy
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* this, we pad PK.seed to the length of a full 64-byte SHA-256 input block.
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* Because of the Merkle-Damgård construction that underlies SHA-256, this
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* allows for reuse of the intermediate SHA-256 state after the initial call to
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* the compression function which improves performance.
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*
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* We pass this hash state around in functions, because otherwise we need to
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* have a global variable.
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*
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* SHAKE256 does not need this state. Because this implementation is generated
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* from a shared code base, we still need to specify some hash_state as it is
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* still passed around. We chose to use an `int` as a placeholder for this
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* purpose.
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*/
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typedef int hash_state;
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#endif
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