poseidon_permutation/permutation.rs
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#![allow(non_snake_case)]
use decaf377::Fq;
use poseidon_parameters::v1::{Alpha, MatrixOperations, PoseidonParameters};
/// Represents a generic instance of `Poseidon`.
///
/// Intended for generic fixed-width hashing.
pub struct Instance<
'a,
const STATE_SIZE: usize,
const STATE_SIZE_MINUS_1: usize,
const NUM_MDS_ELEMENTS: usize,
const NUM_STATE_SIZE_MINUS_1_ELEMENTS: usize,
const NUM_ROUND_ROWS: usize,
const NUM_ROUND_COLS: usize,
const NUM_ROUND_ELEMENTS: usize,
const NUM_PARTIAL_ROUNDS: usize,
> {
/// Parameters for this instance of Poseidon.
parameters: &'a PoseidonParameters<
STATE_SIZE,
STATE_SIZE_MINUS_1,
NUM_MDS_ELEMENTS,
NUM_STATE_SIZE_MINUS_1_ELEMENTS,
NUM_ROUND_ROWS,
NUM_ROUND_COLS,
NUM_ROUND_ELEMENTS,
NUM_PARTIAL_ROUNDS,
>,
/// Inner state.
state_words: [Fq; STATE_SIZE],
}
impl<
'a,
const STATE_SIZE: usize,
const STATE_SIZE_MINUS_1: usize,
const NUM_MDS_ELEMENTS: usize,
const NUM_STATE_SIZE_MINUS_1_ELEMENTS: usize,
const NUM_ROUND_ROWS: usize,
const NUM_ROUND_COLS: usize,
const NUM_ROUND_ELEMENTS: usize,
const NUM_PARTIAL_ROUNDS: usize,
>
Instance<
'a,
STATE_SIZE,
STATE_SIZE_MINUS_1,
NUM_MDS_ELEMENTS,
NUM_STATE_SIZE_MINUS_1_ELEMENTS,
NUM_ROUND_ROWS,
NUM_ROUND_COLS,
NUM_ROUND_ELEMENTS,
NUM_PARTIAL_ROUNDS,
>
{
/// Instantiate a new hash function over Fq given `Parameters`.
pub fn new(
parameters: &'a PoseidonParameters<
STATE_SIZE,
STATE_SIZE_MINUS_1,
NUM_MDS_ELEMENTS,
NUM_STATE_SIZE_MINUS_1_ELEMENTS,
NUM_ROUND_ROWS,
NUM_ROUND_COLS,
NUM_ROUND_ELEMENTS,
NUM_PARTIAL_ROUNDS,
>,
) -> Self {
Self {
parameters,
state_words: [Fq::from(0u64); STATE_SIZE],
}
}
/// Fixed width hash from n:1. Outputs a F given `t` input words.
pub fn n_to_1_fixed_hash(&mut self, input_words: &[Fq; STATE_SIZE]) -> Fq {
// Set internal state words.
for (i, input_word) in input_words.iter().enumerate() {
self.state_words[i] = *input_word
}
// Apply Poseidon permutation.
self.permute();
// Emit a single element since this is a n:1 hash.
self.state_words[1]
}
/// Print out internal state.
pub fn output_words(&self) -> [Fq; STATE_SIZE] {
self.state_words
}
/// Permutes the internal state.
///
/// This implementation is based on the optimized Sage implementation
/// `poseidonperm_x3_64_optimized.sage` provided in Appendix B of the Poseidon paper.
fn permute(&mut self) {
let R_f = self.parameters.rounds.full() / 2;
// First chunk of full rounds
for r in 0..R_f {
// Apply `AddRoundConstants` layer
for i in 0..STATE_SIZE {
self.state_words[i] += self.parameters.optimized_arc.0.get_element(r, i);
}
self.full_sub_words();
self.mix_layer_mds();
}
let mut round_constants_counter = R_f;
// Partial rounds
// First part of `AddRoundConstants` layer
for i in 0..STATE_SIZE {
self.state_words[i] += self
.parameters
.optimized_arc
.0
.get_element(round_constants_counter, i);
}
// First full matrix multiplication.
self.mix_layer_mi();
for r in 0..self.parameters.rounds.partial() - 1 {
self.partial_sub_words();
// Rest of `AddRoundConstants` layer, moved to after the S-box layer
round_constants_counter += 1;
self.state_words[0] += self
.parameters
.optimized_arc
.0
.get_element(round_constants_counter, 0);
self.sparse_mat_mul(self.parameters.rounds.partial() - r - 1);
}
// Last partial round
self.partial_sub_words();
self.sparse_mat_mul(0);
round_constants_counter += 1;
// Final full rounds
for _ in 0..R_f {
// Apply `AddRoundConstants` layer
for i in 0..STATE_SIZE {
self.state_words[i] += self
.parameters
.optimized_arc
.0
.get_element(round_constants_counter, i);
}
self.full_sub_words();
self.mix_layer_mds();
round_constants_counter += 1;
}
}
/// Fixed width hash from n:1. Outputs a F given `t` input words. Unoptimized.
pub fn unoptimized_n_to_1_fixed_hash(&mut self, input_words: [Fq; STATE_SIZE]) -> Fq {
// Set internal state words.
for (i, input_word) in input_words.iter().enumerate() {
self.state_words[i] = *input_word
}
// Apply Poseidon permutation.
self.unoptimized_permute();
// Emit a single element since this is a n:1 hash.
self.state_words[1]
}
/// Permutes the internal state.
///
/// This implementation is based on the unoptimized Sage implementation
/// `poseidonperm_x5_254_3.sage` provided in Appendix B of the Poseidon paper.
fn unoptimized_permute(&mut self) {
let R_f = self.parameters.rounds.full() / 2;
let R_P = self.parameters.rounds.partial();
let mut round_constants_counter = 0;
let round_constants = self.parameters.arc.elements();
// First full rounds
for _ in 0..R_f {
// Apply `AddRoundConstants` layer
for i in 0..STATE_SIZE {
self.state_words[i] += round_constants[round_constants_counter];
round_constants_counter += 1;
}
self.full_sub_words();
self.mix_layer_mds();
}
// Partial rounds
for _ in 0..R_P {
// Apply `AddRoundConstants` layer
for i in 0..STATE_SIZE {
self.state_words[i] += round_constants[round_constants_counter];
round_constants_counter += 1;
}
self.partial_sub_words();
self.mix_layer_mds();
}
// Final full rounds
for _ in 0..R_f {
// Apply `AddRoundConstants` layer
for i in 0..STATE_SIZE {
self.state_words[i] += round_constants[round_constants_counter];
round_constants_counter += 1;
}
self.full_sub_words();
self.mix_layer_mds();
}
}
/// Applies the partial `SubWords` layer.
fn partial_sub_words(&mut self) {
match self.parameters.alpha {
Alpha::Exponent(exp) => self.state_words[0] = (self.state_words[0]).power([exp as u64]),
Alpha::Inverse => self.state_words[0] = Fq::from(1u64) / self.state_words[0],
}
}
/// Applies the full `SubWords` layer.
fn full_sub_words(&mut self) {
match self.parameters.alpha {
Alpha::Exponent(exp) => {
for i in 0..STATE_SIZE {
self.state_words[i] = self.state_words[i].power([exp as u64]);
}
}
Alpha::Inverse => {
for i in 0..STATE_SIZE {
self.state_words[i] = Fq::from(1u64) / self.state_words[i];
}
}
}
}
/// Applies the `MixLayer` using the M_i matrix.
fn mix_layer_mi(&mut self) {
let mut new_state_words = [Fq::from(0u64); STATE_SIZE];
for (i, row) in self.parameters.optimized_mds.M_i.iter_rows().enumerate() {
let sum = row
.iter()
.zip(&self.state_words)
.map(|(x, y)| *x * *y)
.sum();
new_state_words[i] = sum;
}
self.state_words = new_state_words;
}
/// Applies the `MixLayer` using the MDS matrix.
fn mix_layer_mds(&mut self) {
let mut new_state_words = [Fq::from(0u64); STATE_SIZE];
for (i, row) in self.parameters.mds.0 .0.iter_rows().enumerate() {
let sum = row
.iter()
.zip(&self.state_words)
.map(|(x, y)| *x * *y)
.sum();
new_state_words[i] = sum;
}
self.state_words = new_state_words;
}
/// This is `cheap_matrix_mul` in the Sage spec
fn sparse_mat_mul(&mut self, round_number: usize) {
// mul_row = [(state_words[0] * v[i]) for i in range(0, t-1)]
// add_row = [(mul_row[i] + state_words[i+1]) for i in range(0, t-1)]
let mut add_row = [Fq::from(0u64); STATE_SIZE_MINUS_1];
for (i, x) in self.parameters.optimized_mds.v_collection[round_number]
.elements
.iter()
.enumerate()
{
add_row[i] = *x * self.state_words[0] + self.state_words[i + 1];
}
// column_1 = [M_0_0] + w_hat
// state_words_new[0] = sum([column_1[i] * state_words[i] for i in range(0, t)])
// state_words_new = [state_words_new[0]] + add_row
self.state_words[0] = self.parameters.optimized_mds.M_00 * self.state_words[0]
+ self.parameters.optimized_mds.w_hat_collection[round_number]
.elements
.iter()
.zip(self.state_words[1..STATE_SIZE].iter())
.map(|(x, y)| *x * *y)
.sum::<Fq>();
self.state_words[1..STATE_SIZE].copy_from_slice(&add_row[..(STATE_SIZE - 1)]);
}
}