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

// Copyright 2023 RISC Zero, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

use alloc::vec::Vec;

use risc0_core::field::{Elem, ExtElem, RootsOfUnity};

use super::VerifyHal;
use crate::{
    core::{config::ConfigHash, log2_ceil},
    verify::{merkle::MerkleTreeVerifier, read_iop::ReadIOP, VerificationError},
    FRI_FOLD, FRI_FOLD_PO2, FRI_MIN_DEGREE, INV_RATE, QUERIES,
};

/// VerifyRoundInfo contains the data against which the queries for a particular
/// round are checked. This includes the Merkle tree top row data, as well as
/// the size of the domain of the polynomial, and the mixing parameter.
struct VerifyRoundInfo<'a, H: VerifyHal> {
    domain: usize,
    merkle: MerkleTreeVerifier<'a, H>,
    mix: H::ExtElem,
}

impl<'a, H: VerifyHal> VerifyRoundInfo<'a, H> {
    pub fn new(iop: &mut ReadIOP<'a, H::Field, H::Rng>, in_domain: usize) -> Self {
        let domain = in_domain / FRI_FOLD;
        VerifyRoundInfo {
            domain,
            merkle: MerkleTreeVerifier::new(iop, domain, FRI_FOLD * H::ExtElem::EXT_SIZE, QUERIES),
            mix: iop.random_ext_elem(),
        }
    }

    pub fn verify_query(
        &mut self,
        hal: &H,
        iop: &mut ReadIOP<'a, H::Field, H::Rng>,
        pos: &mut usize,
        goal: &mut H::ExtElem,
    ) -> Result<(), VerificationError> {
        let quot = *pos / self.domain;
        let group = *pos % self.domain;
        // Get the column data
        let data = self.merkle.verify(iop, group)?;
        let data_ext: Vec<_> = (0..FRI_FOLD)
            .map(|i| {
                let mut inps = Vec::with_capacity(H::ExtElem::EXT_SIZE);
                for j in 0..H::ExtElem::EXT_SIZE {
                    inps.push(data[j * FRI_FOLD + i]);
                }
                H::ExtElem::from_subelems(inps)
            })
            .collect();
        // Check the existing goal
        if data_ext[quot] != *goal {
            return Err(VerificationError::InvalidProof);
        }
        // Compute the new goal + pos
        let root_po2 = log2_ceil(FRI_FOLD * self.domain);
        let inv_wk = H::Elem::ROU_REV[root_po2].pow(group);
        *goal = hal.fold_eval(&mut data_ext.try_into().unwrap(), self.mix * inv_wk);
        *pos = group;
        Ok(())
    }
}

pub fn fri_verify<'a, H: VerifyHal + 'a, F>(
    hal: &'a H,
    iop: &mut ReadIOP<'a, H::Field, H::Rng>,
    mut degree: usize,
    mut inner: F,
) -> Result<(), VerificationError>
where
    F: FnMut(&mut ReadIOP<'a, H::Field, H::Rng>, usize) -> Result<H::ExtElem, VerificationError>,
{
    let orig_domain = INV_RATE * degree;
    let mut domain = orig_domain;
    // Prep the folding verfiers
    let rounds_capacity =
        (log2_ceil((degree + FRI_FOLD - 1) / FRI_FOLD) + FRI_FOLD_PO2 - 1) / FRI_FOLD_PO2;
    let mut rounds = Vec::with_capacity(rounds_capacity);
    while degree > FRI_MIN_DEGREE {
        rounds.push(VerifyRoundInfo::new(iop, domain));
        domain /= FRI_FOLD;
        degree /= FRI_FOLD;
    }
    // We want to minimize reallocation in verify, so make sure we
    // didn't have to reallocate.
    assert!(
        rounds.len() < rounds_capacity,
        "Did not allocate enough rounds; needed {} for degree {} but only allocated {}",
        rounds.len(),
        degree,
        rounds_capacity
    );
    // Grab the final coeffs + commit
    let final_coeffs = iop.read_field_elem_slice(H::ExtElem::EXT_SIZE * degree);
    let final_digest = H::Hash::hash_elem_slice(final_coeffs);
    iop.commit(&final_digest);
    // Get the generator for the final polynomial evaluations
    let gen = <H::Elem as RootsOfUnity>::ROU_FWD[log2_ceil(domain)];
    // Do queries
    let mut poly_buf: Vec<H::ExtElem> = Vec::with_capacity(degree);
    for _ in 0..QUERIES {
        let mut pos = iop.random_bits(log2_ceil(orig_domain)) as usize;
        // Do the 'inner' verification for this index
        let mut goal = inner(iop, pos)?;
        // Verify the per-round proofs
        for round in &mut rounds {
            round.verify_query(hal, iop, &mut pos, &mut goal)?;
        }
        // Do final verification
        let x = gen.pow(pos);

        poly_buf.clear();
        poly_buf.extend((0..degree).map(|i| {
            H::ExtElem::from_subelems(
                (0..H::ExtElem::EXT_SIZE).map(|j| final_coeffs[j * degree + i]),
            )
        }));
        let fx = hal.poly_eval(poly_buf.as_slice(), H::ExtElem::from_subfield(&x));
        if fx != goal {
            return Err(VerificationError::InvalidProof);
        }
    }
    Ok(())
}