package bls12-381

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Implementation of an instantiation of Poseidon over the scalar field of BLS12-381 for a security of 128 bits and with the permutation x^5. The parameters of the instantiation are:

  • state size = 3
  • number of full rounds = 8
  • number partial rounds = 56
  • the partial rounds run the sbox on the last element of the state

These parameters have been generated using security_parameters.ml from Mec.

The linear layer constants and the round keys can be generated using generate_ark.ml and generate_mds.sage from Mec. The constants must be loaded at the top level using Poseidon128.constants_init.

The current implementation only provides the functions to run a permutation. The user is responsible to build a hash function on top of it.

type ctxt

Context of the permutation

val constants_init : Fr.t array -> Fr.t array array -> unit

constants_init ark mds initializes the constants for Poseidon.

Warnings:

  • The function does not verify the parameters are secured
  • This function must be called before calling init, apply_permutation and get
val init : Fr.t -> Fr.t -> Fr.t -> ctxt

init a b c returns a new context with an initialised state with the value [a, b, c].

val apply_permutation : ctxt -> unit

apply_permutation ctxt applies a permutation on the state. The context is modified.

val get : ctxt -> Fr.t * Fr.t * Fr.t

get ctxt returns the state of the permutation

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