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
176
177
178
179
180
181
182
183


use std::hash::{Hash, Hasher};
use std::cmp::Ordering;

use ring::digest::Algorithm;

use tree::Tree;
use hashutils::HashUtils;

/// An inclusion proof represent the fact that a `value` is a member
/// of a `MerkleTree` with root hash `root_hash`, and hash function `algorithm`.
#[derive(Clone, Debug)]
pub struct Proof<T> {
    /// The hashing algorithm used in the original `MerkleTree`
    pub algorithm: &'static Algorithm,

    /// The hash of the root of the original `MerkleTree`
    pub root_hash: Vec<u8>,

    /// The first `Lemma` of the `Proof`
    pub lemma: Lemma,

    /// The value concerned by this `Proof`
    pub value: T,
}

impl<T: PartialEq> PartialEq for Proof<T> {
    fn eq(&self, other: &Proof<T>) -> bool {
        self.root_hash == other.root_hash && self.lemma == other.lemma && self.value == other.value
    }
}

impl<T: Eq> Eq for Proof<T> {}

impl<T: Ord> PartialOrd for Proof<T> {
    fn partial_cmp(&self, other: &Proof<T>) -> Option<Ordering> {
        Some(self.cmp(other))
    }
}

impl<T: Ord> Ord for Proof<T> {
    fn cmp(&self, other: &Proof<T>) -> Ordering {
        self.root_hash
            .cmp(&other.root_hash)
            .then(self.value.cmp(&other.value))
            .then_with(|| self.lemma.cmp(&other.lemma))
    }
}

impl<T: Hash> Hash for Proof<T> {
    fn hash<H: Hasher>(&self, state: &mut H) {
        self.root_hash.hash(state);
        self.lemma.hash(state);
        self.value.hash(state);
    }
}

impl<T> Proof<T> {
    /// Constructs a new `Proof`
    pub fn new(algo: &'static Algorithm, root_hash: Vec<u8>, lemma: Lemma, value: T) -> Self {
        Proof {
            algorithm: algo,
            root_hash: root_hash,
            lemma: lemma,
            value: value,
        }
    }

    /// Checks whether this inclusion proof is well-formed,
    /// and whether its root hash matches the given `root_hash`.
    pub fn validate(&self, root_hash: &[u8]) -> bool {
        if self.root_hash != root_hash || self.lemma.node_hash != root_hash {
            return false;
        }

        self.validate_lemma(&self.lemma)
    }

    fn validate_lemma(&self, lemma: &Lemma) -> bool {
        match lemma.sub_lemma {

            None => lemma.sibling_hash.is_none(),

            Some(ref sub) => {
                match lemma.sibling_hash {
                    None => false,

                    Some(Positioned::Left(ref hash)) => {
                        let combined = self.algorithm.hash_nodes(hash, &sub.node_hash);
                        let hashes_match = combined.as_ref() == lemma.node_hash.as_slice();
                        hashes_match && self.validate_lemma(sub)
                    }

                    Some(Positioned::Right(ref hash)) => {
                        let combined = self.algorithm.hash_nodes(&sub.node_hash, hash);
                        let hashes_match = combined.as_ref() == lemma.node_hash.as_slice();
                        hashes_match && self.validate_lemma(sub)
                    }

                }
            }
        }
    }
}


/// A `Lemma` holds the hash of a node, the hash of its sibling node,
/// and a sub lemma, whose `node_hash`, when combined with this `sibling_hash`
/// must be equal to this `node_hash`.
#[derive(Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct Lemma {
    pub node_hash: Vec<u8>,
    pub sibling_hash: Option<Positioned<Vec<u8>>>,
    pub sub_lemma: Option<Box<Lemma>>,
}

impl Lemma {
    /// Attempts to generate a proof that the a value with hash `needle` is a member of the given `tree`.
    pub fn new<T>(tree: &Tree<T>, needle: &[u8]) -> Option<Lemma> {
        match *tree {
            Tree::Empty { .. } => None,

            Tree::Leaf { ref hash, .. } => Lemma::new_leaf_proof(hash, needle),

            Tree::Node {
                ref hash,
                ref left,
                ref right,
            } => Lemma::new_tree_proof(hash, needle, left, right),
        }
    }

    fn new_leaf_proof(hash: &[u8], needle: &[u8]) -> Option<Lemma> {
        if *hash == *needle {
            Some(Lemma {
                node_hash: hash.into(),
                sibling_hash: None,
                sub_lemma: None,
            })
        } else {
            None
        }
    }

    fn new_tree_proof<T>(
        hash: &[u8],
        needle: &[u8],
        left: &Tree<T>,
        right: &Tree<T>,
    ) -> Option<Lemma> {
        Lemma::new(left, needle)
            .map(|lemma| {
                let right_hash = right.hash().clone();
                let sub_lemma = Some(Positioned::Right(right_hash));
                (lemma, sub_lemma)
            })
            .or_else(|| {
                let sub_lemma = Lemma::new(right, needle);
                sub_lemma.map(|lemma| {
                    let left_hash = left.hash().clone();
                    let sub_lemma = Some(Positioned::Left(left_hash));
                    (lemma, sub_lemma)
                })
            })
            .map(|(sub_lemma, sibling_hash)| {
                Lemma {
                    node_hash: hash.into(),
                    sibling_hash: sibling_hash,
                    sub_lemma: Some(Box::new(sub_lemma)),
                }
            })
    }
}

/// Tags a value so that we know from which branch of a `Tree` (if any) it was found.
#[derive(Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub enum Positioned<T> {
    /// The value was found in the left branch
    Left(T),

    /// The value was found in the right branch
    Right(T),
}