p3_poseidon/
lib.rs

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1//! The Poseidon permutation.
2
3#![no_std]
4
5extern crate alloc;
6
7use alloc::vec::Vec;
8
9use p3_field::{FieldAlgebra, PrimeField};
10use p3_mds::MdsPermutation;
11use p3_symmetric::{CryptographicPermutation, Permutation};
12use rand::distributions::Standard;
13use rand::prelude::Distribution;
14use rand::Rng;
15
16/// The Poseidon permutation.
17#[derive(Clone, Debug)]
18pub struct Poseidon<F, Mds, const WIDTH: usize, const ALPHA: u64> {
19    half_num_full_rounds: usize,
20    num_partial_rounds: usize,
21    constants: Vec<F>,
22    mds: Mds,
23}
24
25impl<F, Mds, const WIDTH: usize, const ALPHA: u64> Poseidon<F, Mds, WIDTH, ALPHA>
26where
27    F: PrimeField,
28{
29    /// Create a new Poseidon configuration.
30    ///
31    /// # Panics
32    /// Number of constants must match WIDTH times `num_rounds`; panics otherwise.
33    pub fn new(
34        half_num_full_rounds: usize,
35        num_partial_rounds: usize,
36        constants: Vec<F>,
37        mds: Mds,
38    ) -> Self {
39        let num_rounds = 2 * half_num_full_rounds + num_partial_rounds;
40        assert_eq!(constants.len(), WIDTH * num_rounds);
41        Self {
42            half_num_full_rounds,
43            num_partial_rounds,
44            constants,
45            mds,
46        }
47    }
48
49    pub fn new_from_rng<R: Rng>(
50        half_num_full_rounds: usize,
51        num_partial_rounds: usize,
52        mds: Mds,
53        rng: &mut R,
54    ) -> Self
55    where
56        Standard: Distribution<F>,
57    {
58        let num_rounds = 2 * half_num_full_rounds + num_partial_rounds;
59        let num_constants = WIDTH * num_rounds;
60        let constants = rng
61            .sample_iter(Standard)
62            .take(num_constants)
63            .collect::<Vec<_>>();
64        Self {
65            half_num_full_rounds,
66            num_partial_rounds,
67            constants,
68            mds,
69        }
70    }
71
72    fn half_full_rounds<FA>(&self, state: &mut [FA; WIDTH], round_ctr: &mut usize)
73    where
74        FA: FieldAlgebra<F = F>,
75        Mds: MdsPermutation<FA, WIDTH>,
76    {
77        for _ in 0..self.half_num_full_rounds {
78            self.constant_layer(state, *round_ctr);
79            Self::full_sbox_layer(state);
80            self.mds.permute_mut(state);
81            *round_ctr += 1;
82        }
83    }
84
85    fn partial_rounds<FA>(&self, state: &mut [FA; WIDTH], round_ctr: &mut usize)
86    where
87        FA: FieldAlgebra<F = F>,
88        Mds: MdsPermutation<FA, WIDTH>,
89    {
90        for _ in 0..self.num_partial_rounds {
91            self.constant_layer(state, *round_ctr);
92            Self::partial_sbox_layer(state);
93            self.mds.permute_mut(state);
94            *round_ctr += 1;
95        }
96    }
97
98    fn full_sbox_layer<FA>(state: &mut [FA; WIDTH])
99    where
100        FA: FieldAlgebra<F = F>,
101    {
102        for x in state.iter_mut() {
103            *x = x.exp_const_u64::<ALPHA>();
104        }
105    }
106
107    fn partial_sbox_layer<FA>(state: &mut [FA; WIDTH])
108    where
109        FA: FieldAlgebra<F = F>,
110    {
111        state[0] = state[0].exp_const_u64::<ALPHA>();
112    }
113
114    fn constant_layer<FA>(&self, state: &mut [FA; WIDTH], round: usize)
115    where
116        FA: FieldAlgebra<F = F>,
117    {
118        for (i, x) in state.iter_mut().enumerate() {
119            *x += FA::from_f(self.constants[round * WIDTH + i]);
120        }
121    }
122}
123
124impl<FA, Mds, const WIDTH: usize, const ALPHA: u64> Permutation<[FA; WIDTH]>
125    for Poseidon<FA::F, Mds, WIDTH, ALPHA>
126where
127    FA: FieldAlgebra,
128    FA::F: PrimeField,
129    Mds: MdsPermutation<FA, WIDTH>,
130{
131    fn permute_mut(&self, state: &mut [FA; WIDTH]) {
132        let mut round_ctr = 0;
133        self.half_full_rounds(state, &mut round_ctr);
134        self.partial_rounds(state, &mut round_ctr);
135        self.half_full_rounds(state, &mut round_ctr);
136    }
137}
138
139impl<FA, Mds, const WIDTH: usize, const ALPHA: u64> CryptographicPermutation<[FA; WIDTH]>
140    for Poseidon<FA::F, Mds, WIDTH, ALPHA>
141where
142    FA: FieldAlgebra,
143    FA::F: PrimeField,
144    Mds: MdsPermutation<FA, WIDTH>,
145{
146}
p3_poseidon/lib.rs

p3_poseidon/
lib.rs
