1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97

use crate::{Poseidon, PoseidonLeaf, Scalar, MERKLE_ARITY, MERKLE_HEIGHT};
use std::ops;

/// Set of pairs (idx, Hash) to reconstruct the merkle root.
/// For every level of the tree,
/// Required information to reconstruct the merkle root.
///
/// For every level of the tree, there is an index, and a slice of leaves.
///
/// The index will be the position in which the previously calculated information should be
/// inserted.
///
/// The leaves will define the other elements required to perform the hash for that level of the
/// tree.
#[derive(Debug, Copy, Clone, PartialEq)]
pub struct Proof<T: PoseidonLeaf> {
    pos: usize,
    data: [(usize, [Option<T>; MERKLE_ARITY]); MERKLE_HEIGHT],
}

impl<T: PoseidonLeaf> Default for Proof<T> {
    fn default() -> Self {
        Proof {
            pos: 0,
            data: [(0, [None; MERKLE_ARITY]); MERKLE_HEIGHT],
        }
    }
}

impl<T: PoseidonLeaf> Proof<T> {
    pub(crate) fn push(&mut self, idx: usize, leaves: &[Option<T>]) {
        let (i, proof) = &mut self.data[self.pos];

        proof.copy_from_slice(leaves);
        *i = idx;

        self.pos += 1;
    }

    /// Return the raw proof data
    pub fn data(&self) -> &[(usize, [Option<T>; MERKLE_ARITY]); MERKLE_HEIGHT] {
        &self.data
    }

    /// Verify if the provided leaf corresponds to the proof in the merkle construction
    pub fn verify(&self, leaf: &T, root: &T) -> bool
    where
        Scalar: ops::Mul<T, Output = T>,
    {
        let mut leaf = *leaf;
        let mut h = Poseidon::default();

        for i in 0..self.data.len() {
            let (idx, data) = self.data[i];

            h.replace(&data[0..MERKLE_ARITY]);
            h.insert_unchecked(idx, leaf);

            leaf = h.hash();
        }

        &leaf == root
    }
}

#[cfg(test)]
mod tests {
    use crate::*;

    #[test]
    fn proof_verify() {
        let mut t = MerkleTree::<Scalar>::default();
        for i in 0..MERKLE_WIDTH {
            t.insert_unchecked(i, Scalar::from(i as u64));
        }

        let root = t.root();
        let i = MERKLE_WIDTH / 3;

        let proof = t.proof_index(i);
        assert!(proof.verify(&Scalar::from(i as u64), &root));
    }

    #[test]
    fn proof_verify_failure() {
        let mut t = MerkleTree::<Scalar>::default();
        for i in 0..MERKLE_WIDTH {
            t.insert_unchecked(i, Scalar::from(i as u64));
        }

        let root = t.root();
        let i = MERKLE_WIDTH / 3;

        let proof = t.proof_index(i + 1);
        assert!(!proof.verify(&Scalar::from(i as u64), &root));
    }
}