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62 lines
1.7 KiB
Markdown
62 lines
1.7 KiB
Markdown
Nim implementation of Poseidon2
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===============================
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Experimental implementation of the [Poseidon 2][1] cryptographic hash function,
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specialized to BN254 and t=3. Uses the [constantine][2] library for
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cryptographic primitives. Neither completeness nor correctness are guaranteed at
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this moment in time.
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Installation
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------------
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Use the [Nimble][3] package manager to add `poseidon2` to an existing
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project. Add the following to its .nimble file:
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```nim
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requires "poseidon2 >= 0.1.0 & < 0.2.0"
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```
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Usage
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-----
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Hashing bytes into a field element with the sponge construction:
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```nim
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import poseidon2
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let input = [1'u8, 2'u8, 3'u8] # some bytes that you want to hash
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let digest: F = Sponge.digest(input) # a field element
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```
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Converting a field element into bytes:
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```nim
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let output: array[32, byte] = digest.toBytes
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```
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Combining field elements, useful for constructing a binary Merkle tree:
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```nim
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let left = Sponge.digest([1'u8, 2'u8, 3'u8])
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let right = Sponge.digest([4'u8, 5'u8, 6'u8])
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let combination = compress(left, right)
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```
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Compatbility
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------------
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For Poseidon2, because of a historical accident, there are unfortunately TWO
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different sets of "standard" parameters, which is obviously bad for cross-project compatibility.
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The switchover happened in commit #bb476b9ca38198cf5092487283c8b8c5d4317c4e in
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HorizenLab's reference repo. Both versions are safe to use though.
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To resolve this issue, since version 0.1.1, we implement both sets (though the default
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is the "old" set of round constants, so that we are backward compatible. This may
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or may not change in the future.)
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Links
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-----
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[1]: https://eprint.iacr.org/2023/323.pdf
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[2]: https://github.com/mratsim/constantine
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[3]: https://github.com/nim-lang/nimble
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