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
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175

use ff::PrimeField;
use group::{Curve, GroupEncoding};
use jubjub::{ExtendedNielsPoint, ExtendedPoint, Fr, SubgroupPoint};
use lazy_static::lazy_static;
use std::io::Read;
use std::ops::AddAssign;
use zcash_params::GENERATORS;
use zcash_primitives::constants::PEDERSEN_HASH_CHUNKS_PER_GENERATOR;

lazy_static! {
    pub static ref GENERATORS_EXP: Vec<ExtendedNielsPoint> = read_generators_bin();
}

fn read_generators_bin() -> Vec<ExtendedNielsPoint> {
    let mut generators_bin = GENERATORS;
    let mut gens: Vec<ExtendedNielsPoint> = vec![];
    gens.reserve_exact(3 * 32 * 256);
    for _i in 0..3 {
        for _j in 0..32 {
            for _k in 0..256 {
                let mut bb = [0u8; 32];
                generators_bin.read_exact(&mut bb).unwrap();
                let p = ExtendedPoint::from(SubgroupPoint::from_bytes_unchecked(&bb).unwrap())
                    .to_niels();
                gens.push(p);
            }
        }
    }
    gens
}

macro_rules! accumulate_scalar {
    ($acc: ident, $cur: ident, $x: expr) => {
        let mut tmp = $cur;
        if $x & 1 != 0 {
            tmp.add_assign(&$cur);
        }
        $cur = $cur.double();
        if $x & 2 != 0 {
            tmp.add_assign(&$cur);
        }
        if $x & 4 != 0 {
            tmp = tmp.neg();
        }

        $acc.add_assign(&tmp);
    };
}

pub type Hash = [u8; 32];

pub fn pedersen_hash(depth: u8, left: &Hash, right: &Hash) -> Hash {
    let p = pedersen_hash_inner(depth, left, right);

    p.to_affine().get_u().to_repr()
}

pub fn pedersen_hash_inner(depth: u8, left: &Hash, right: &Hash) -> ExtendedPoint {
    let mut result = ExtendedPoint::identity();
    let mut bitoffset = 0;
    let mut byteoffset = 0;
    let mut r_byteoffset = 0;

    let mut acc = Fr::zero();
    let mut cur = Fr::one();

    let a = depth & 7;
    let b = depth >> 3;
    accumulate_scalar!(acc, cur, a);
    cur = cur.double().double().double();
    // println!("{}", hex::encode(acc.to_bytes()));

    accumulate_scalar!(acc, cur, b);
    cur = cur.double().double().double();
    // println!("{}", hex::encode(acc.to_bytes()));

    let mut i_generator = 0;
    let mut chunks_remaining = PEDERSEN_HASH_CHUNKS_PER_GENERATOR - 3;

    let mut r = (left[0] as u16) | (left[1] as u16) << 8;
    let x = (r >> bitoffset) & 7;
    accumulate_scalar!(acc, cur, x);
    cur = cur.double().double().double();

    for _c in 0..169 {
        bitoffset += 3;
        let x = (r >> bitoffset) & 7;
        accumulate_scalar!(acc, cur, x);
        if bitoffset >= 8 {
            bitoffset -= 8;
            byteoffset += 1;
            if byteoffset < 31 {
                r = (r >> 8) | (left[byteoffset + 1] as u16) << 8;
            } else if byteoffset == 31 {
                r = ((r >> 7) & 0xFF) | (right[0] as u16) << 8;
                bitoffset += 1;
            } else if byteoffset < 63 {
                r = (r >> 8) | (right[r_byteoffset + 1] as u16) << 8;
                r_byteoffset += 1;
            } else if byteoffset == 63 {
                r >>= 8;
            }
        }

        chunks_remaining -= 1;
        if chunks_remaining == 0 {
            // println!("++ {}", hex::encode(acc.to_bytes()));

            result += generator_multiplication(&acc, &GENERATORS_EXP, i_generator);

            i_generator += 1;
            acc = Fr::zero();
            cur = Fr::one();
            chunks_remaining = PEDERSEN_HASH_CHUNKS_PER_GENERATOR
        } else {
            cur = cur.double().double().double(); // 2^4 * cur
        }
    }
    result += generator_multiplication(&acc, &GENERATORS_EXP, i_generator);
    result
}

fn generator_multiplication(
    acc: &Fr,
    gens: &[ExtendedNielsPoint],
    i_generator: u32,
) -> ExtendedPoint {
    let acc = acc.to_repr();

    let mut tmp = jubjub::ExtendedPoint::identity();
    for (i, &j) in acc.iter().enumerate() {
        let offset = (i_generator * 32 + i as u32) * 256 + j as u32;
        let x = gens[offset as usize];
        tmp += x;
    }
    tmp
}

#[cfg(test)]
mod tests {
    use crate::hash::pedersen_hash;
    use rand::{thread_rng, RngCore};
    use zcash_primitives::merkle_tree::Hashable;
    use zcash_primitives::sapling::Node;

    #[test]
    fn test_hash() {
        let mut r = thread_rng();

        for _ in 0..1 {
            let mut a = [0u8; 32];
            r.fill_bytes(&mut a);
            let mut b = [0u8; 32];
            r.fill_bytes(&mut b);
            let depth = (r.next_u32() % 64) as u8;
            let depth = depth.min(62);

            // let sa = "767a9a7e989289efdfa69c4c8e985c31f3c2c0353f20a80f572854206f077f86";
            // let sb = "944c46945a9e7a0a753850bd90f69d44ac884b60244a9f8eacf3a2aeddd08d6e";
            // a.copy_from_slice(&hex::decode(sa).unwrap());
            // b.copy_from_slice(&hex::decode(sb).unwrap());
            // println!("A: {}", hex::encode(a));
            // println!("B: {}", hex::encode(b));

            let node1 = Node::new(a);
            let node2 = Node::new(b);
            let hash = Node::combine(depth as usize, &node1, &node2);
            let hash2 = pedersen_hash(depth, &a, &b);
            // println!("Reference Hash: {}", hex::encode(hash.repr));
            // println!("This Hash:      {}", hex::encode(hash2));
            // need to expose repr for this check
            assert_eq!(hash.repr, hash2);
        }
    }
}