fuchsia_merkle/
util.rs

1// Copyright 2018 The Fuchsia Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5use bssl_crypto::digest::Sha256;
6use std::mem::{size_of, size_of_val};
7
8use crate::{BLOCK_SIZE, HASH_SIZE, Hash};
9
10pub(crate) const HASHES_PER_BLOCK: usize = BLOCK_SIZE / HASH_SIZE;
11
12type BlockIdentity = [u8; size_of::<u64>() + size_of::<u32>()];
13
14/// Generate the bytes representing a block's identity.
15fn make_identity(length: usize, level: usize, offset: usize) -> BlockIdentity {
16    let offset_or_level = (offset as u64 | level as u64).to_le_bytes();
17    let length = (length as u32).to_le_bytes();
18    let mut ret: BlockIdentity = [0; size_of::<BlockIdentity>()];
19    let (ret_offset_or_level, ret_length) = ret.split_at_mut(size_of_val(&offset_or_level));
20    ret_offset_or_level.copy_from_slice(&offset_or_level);
21    ret_length.copy_from_slice(&length);
22    ret
23}
24
25/// Compute the merkle hash of a block of data.
26///
27/// A merkle hash is the SHA-256 hash of a block of data with a small header built from the length
28/// of the data, the level of the tree (0 for data blocks), and the offset into the level. The
29/// block will be zero filled if its len is less than [`BLOCK_SIZE`], except for when the first
30/// data block is completely empty.
31///
32/// # Panics
33///
34/// Panics if `block.len()` exceeds [`BLOCK_SIZE`] or if `offset` is not aligned to [`BLOCK_SIZE`]
35pub fn hash_block(block: &[u8], offset: usize) -> Hash {
36    assert!(block.len() <= BLOCK_SIZE);
37    assert!(offset.is_multiple_of(BLOCK_SIZE));
38
39    let mut hasher = Sha256::new();
40    hasher.update(&make_identity(block.len(), 0, offset));
41    hasher.update(block);
42    // Zero fill block up to BLOCK_SIZE. As a special case, if the first data block is completely
43    // empty, it is not zero filled.
44    if block.len() != BLOCK_SIZE && !(block.is_empty() && offset == 0) {
45        update_with_zeros(&mut hasher, BLOCK_SIZE - block.len());
46    }
47
48    Hash::from(hasher.digest())
49}
50
51/// Compute the merkle hash of a block of hashes.
52///
53/// Both `hash_block` and `hash_hashes` will zero fill incomplete buffers, but unlike `hash_block`,
54/// which includes the actual buffer size in the hash, `hash_hashes` always uses a size of
55/// [`BLOCK_SIZE`] when computing the hash. Therefore, the following inputs are equivalent:
56/// ```ignore
57/// let data_hash = "15ec7bf0b50732b49f8228e07d24365338f9e3ab994b00af08e5a3bffe55fd8b"
58///     .parse()
59///     .unwrap();
60/// let zero_hash = "0000000000000000000000000000000000000000000000000000000000000000"
61///     .parse()
62///     .unwrap();
63/// let hash_of_single_hash = fuchsia_merkle::hash_hashes(&vec![data_hash], 0, 0);
64/// let hash_of_single_hash_and_zero_hash =
65///     fuchsia_merkle::hash_hashes(&vec![data_hash, zero_hash], 0, 0);
66/// assert_eq!(hash_of_single_hash, hash_of_single_hash_and_zero_hash);
67/// ```
68///
69/// # Panics
70///
71/// Panics if any of the following conditions are met:
72/// - `hashes.len()` is 0
73/// - `hashes.len() > HASHES_PER_BLOCK`
74/// - `level` is 0
75/// - `offset` is not aligned to [`BLOCK_SIZE`]
76pub(crate) fn hash_hashes(hashes: &[Hash], level: usize, offset: usize) -> Hash {
77    assert_ne!(hashes.len(), 0);
78    assert!(hashes.len() <= HASHES_PER_BLOCK);
79    assert!(level > 0);
80    assert!(offset.is_multiple_of(BLOCK_SIZE));
81
82    let mut hasher = make_hash_hasher(HASHES_PER_BLOCK, level, offset);
83    for hash in hashes.iter() {
84        hasher.update(hash.as_bytes());
85    }
86    if hashes.len() != HASHES_PER_BLOCK {
87        update_with_zeros(&mut hasher, (HASHES_PER_BLOCK - hashes.len()) * HASH_SIZE);
88    }
89    Hash::from(hasher.digest())
90}
91
92/// Updates `hasher` with `count` zeros.
93pub(crate) fn update_with_zeros(hasher: &mut Sha256, mut count: usize) {
94    const BUF_SIZE: usize = 512;
95    const ZEROS: [u8; BUF_SIZE] = [0; BUF_SIZE];
96    while count >= BUF_SIZE {
97        count -= BUF_SIZE;
98        hasher.update(&ZEROS);
99    }
100    if count > 0 {
101        hasher.update(&ZEROS[0..count]);
102    }
103}
104
105/// Creates a new [`Sha256`] for hashing blocks of hashes. The hasher is initialized with the
106/// block's identity.
107pub(crate) fn make_hash_hasher(hashes_per_hash: usize, level: usize, offset: usize) -> Sha256 {
108    debug_assert!(level > 0);
109    let bytes_per_hash = hashes_per_hash * HASH_SIZE;
110    debug_assert!(offset.is_multiple_of(bytes_per_hash));
111    let mut hasher = Sha256::new();
112    hasher.update(&make_identity(bytes_per_hash, level, offset));
113    hasher
114}
115
116#[cfg(test)]
117mod tests {
118    use super::*;
119
120    #[test]
121    fn test_hash_block_empty() {
122        let block = [];
123        let hash = hash_block(&block[..], 0);
124        let expected =
125            "15ec7bf0b50732b49f8228e07d24365338f9e3ab994b00af08e5a3bffe55fd8b".parse().unwrap();
126        assert_eq!(hash, expected);
127    }
128
129    #[test]
130    fn test_hash_block_single() {
131        let block = vec![0xFF; 8192];
132        let hash = hash_block(&block[..], 0);
133        let expected =
134            "68d131bc271f9c192d4f6dcd8fe61bef90004856da19d0f2f514a7f4098b0737".parse().unwrap();
135        assert_eq!(hash, expected);
136    }
137
138    #[test]
139    fn test_hash_hashes_full_block() {
140        let mut leafs = Vec::new();
141        {
142            let block = vec![0xFF; BLOCK_SIZE];
143            for i in 0..HASHES_PER_BLOCK {
144                leafs.push(hash_block(&block, i * BLOCK_SIZE));
145            }
146        }
147        let root = hash_hashes(&leafs, 1, 0);
148        let expected =
149            "1e6e9c870e2fade25b1b0288ac7c216f6fae31c1599c0c57fb7030c15d385a8d".parse().unwrap();
150        assert_eq!(root, expected);
151    }
152
153    #[test]
154    fn test_hash_hashes_zero_pad_same_length() {
155        let data_hash =
156            "15ec7bf0b50732b49f8228e07d24365338f9e3ab994b00af08e5a3bffe55fd8b".parse().unwrap();
157        let zero_hash =
158            "0000000000000000000000000000000000000000000000000000000000000000".parse().unwrap();
159        let hash_of_single_hash = hash_hashes(&[data_hash], 1, 0);
160        let hash_of_single_hash_and_zero_hash = hash_hashes(&[data_hash, zero_hash], 1, 0);
161        assert_eq!(hash_of_single_hash, hash_of_single_hash_and_zero_hash);
162    }
163}
fuchsia_merkle/util.rs

fuchsia_merkle/
util.rs
