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

// Copyright 2022 Risc0, 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.

//! Simple SHA-256 wrappers.

use alloc::{boxed::Box, vec, vec::Vec};
use core::slice;

use sha2::{
    compress256,
    digest::generic_array::{typenum::U64, GenericArray},
    Digest as ShaDigest, Sha256,
};

use crate::{
    fp::Fp,
    fp4::Fp4,
    sha::{Digest, Sha, DIGEST_WORDS},
};

static INIT_256: [u32; DIGEST_WORDS] = [
    0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a, 0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19,
];

#[derive(Clone)]
pub struct Impl {}

fn set_word(buf: &mut [u8], idx: usize, word: u32) {
    buf[(4 * idx)..(4 * idx + 4)].copy_from_slice(&word.to_le_bytes());
}

impl Sha for Impl {
    type DigestPtr = Box<Digest>;

    fn hash_bytes(&self, bytes: &[u8]) -> Self::DigestPtr {
        let mut hasher = Sha256::new();
        hasher.update(bytes);
        Box::new(Digest::new(
            hasher
                .finalize()
                .as_slice()
                .chunks(4)
                .map(|chunk| u32::from_be_bytes(chunk.try_into().unwrap()))
                .collect::<Vec<u32>>()
                .try_into()
                .unwrap(),
        ))
    }

    fn hash_words(&self, words: &[u32]) -> Self::DigestPtr {
        self.hash_bytes(bytemuck::cast_slice(words) as &[u8])
    }

    fn hash_fps(&self, fps: &[Fp]) -> Self::DigestPtr {
        let mut state = INIT_256;
        let mut block: GenericArray<u8, U64> = GenericArray::default();
        let mut off = 0;
        for i in 0..fps.len() {
            set_word(block.as_mut_slice(), off, u32::from(fps[i]));
            off += 1;
            if off == 16 {
                compress256(&mut state, slice::from_ref(&block));
                off = 0;
            }
        }
        if off != 0 {
            block[off * 4..].fill(0);
            compress256(&mut state, slice::from_ref(&block));
        }
        Box::new(Digest::new(state))
    }

    fn hash_fp4s(&self, fp4s: &[Fp4]) -> Self::DigestPtr {
        let mut flat: Vec<Fp> = vec![];
        for i in 0..fp4s.len() {
            for j in 0..4 {
                flat.push(fp4s[i].elems()[j]);
            }
        }
        return self.hash_fps(&flat);
    }

    // Digest two digest into one
    fn hash_pair(&self, a: &Digest, b: &Digest) -> Self::DigestPtr {
        let mut state = INIT_256;
        let mut block: GenericArray<u8, U64> = GenericArray::default();
        for i in 0..8 {
            set_word(block.as_mut_slice(), i, a.as_slice()[i]);
            set_word(block.as_mut_slice(), 8 + i, b.as_slice()[i]);
        }
        compress256(&mut state, slice::from_ref(&block));
        Box::new(Digest::new(state))
    }

    // Generate a new digest by mixing two digests together via XOR,
    // and stores it back in the pool.
    fn mix(&self, pool: &mut Self::DigestPtr, val: &Digest) {
        // CPU based sha can do this in place without generating another digest pointer.
        for (pool_word, val_word) in pool.get_mut().iter_mut().zip(val.get()) {
            *pool_word ^= *val_word;
        }
    }
}

impl core::fmt::Debug for Impl {
    fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
        core::write!(f, "CPU SHA256 implementation")
    }
}

#[cfg(test)]
mod tests {
    use super::Impl;

    #[test]
    fn test_impl() {
        crate::sha::testutil::test_sha_impl(&Impl {})
    }
}