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

// Rust Bitcoin Library
// Written in 2019 by
//     The rust-bitcoin developers.
// To the extent possible under law, the author(s) have dedicated all
// copyright and related and neighboring rights to this software to
// the public domain worldwide. This software is distributed without
// any warranty.
//
// You should have received a copy of the CC0 Public Domain Dedication
// along with this software.
// If not, see <http://creativecommons.org/publicdomain/zero/1.0/>.
//

//! Taproot
//!

use hashes::{sha256, sha256t, Hash};

/// The SHA-256 midstate value for the TapLeaf hash.
const MIDSTATE_TAPLEAF: [u8; 32] = [
    156, 224, 228, 230, 124, 17, 108, 57, 56, 179, 202, 242, 195, 15, 80, 137, 211, 243, 147, 108,
    71, 99, 110, 96, 125, 179, 62, 234, 221, 198, 240, 201,
];
// 9ce0e4e67c116c3938b3caf2c30f5089d3f3936c47636e607db33eeaddc6f0c9

/// The SHA-256 midstate value for the TapBranch hash.
const MIDSTATE_TAPBRANCH: [u8; 32] = [
    35, 168, 101, 169, 184, 164, 13, 167, 151, 124, 30, 4, 196, 158, 36, 111, 181, 190, 19, 118,
    157, 36, 201, 183, 181, 131, 181, 212, 168, 210, 38, 210,
];
// 23a865a9b8a40da7977c1e04c49e246fb5be13769d24c9b7b583b5d4a8d226d2

/// The SHA-256 midstate value for the TapTweak hash.
const MIDSTATE_TAPTWEAK: [u8; 32] = [
    209, 41, 162, 243, 112, 28, 101, 93, 101, 131, 182, 195, 185, 65, 151, 39, 149, 244, 226, 50,
    148, 253, 84, 244, 162, 174, 141, 133, 71, 202, 89, 11,
];
// d129a2f3701c655d6583b6c3b941972795f4e23294fd54f4a2ae8d8547ca590b

/// The SHA-256 midstate value for the TapSigHash hash.
const MIDSTATE_TAPSIGHASH: [u8; 32] = [
    245, 4, 164, 37, 215, 248, 120, 59, 19, 99, 134, 138, 227, 229, 86, 88, 110, 238, 148, 93, 188,
    120, 136, 221, 2, 166, 226, 195, 24, 115, 254, 159,
];
// f504a425d7f8783b1363868ae3e556586eee945dbc7888dd02a6e2c31873fe9f

/// Internal macro to speficy the different taproot tagged hashes.
macro_rules! sha256t_hash_newtype {
    ($newtype:ident, $tag:ident, $midstate:ident, $midstate_len:expr, $docs:meta, $reverse: expr) => {
        /// The tag used for [$newtype].
        pub struct $tag;

        impl sha256t::Tag for $tag {
            fn engine() -> sha256::HashEngine {
                let midstate = sha256::Midstate::from_inner($midstate);
                sha256::HashEngine::from_midstate(midstate, $midstate_len)
            }
        }

        hash_newtype!($newtype, sha256t::Hash<$tag>, 32, $docs, $reverse);
    };
}

// Currently all taproot hashes are defined as being displayed backwards,
// but that can be specified individually per hash.
sha256t_hash_newtype!(TapLeafHash, TapLeafTag, MIDSTATE_TAPLEAF, 64,
    doc="Taproot-tagged hash for tapscript Merkle tree leafs", true
);
sha256t_hash_newtype!(TapBranchHash, TapBranchTag, MIDSTATE_TAPBRANCH, 64,
    doc="Taproot-tagged hash for tapscript Merkle tree branches", true
);
sha256t_hash_newtype!(TapTweakHash, TapTweakTag, MIDSTATE_TAPTWEAK, 64,
    doc="Taproot-tagged hash for public key tweaks", true
);
sha256t_hash_newtype!(TapSighashHash, TapSighashTag, MIDSTATE_TAPSIGHASH, 64,
    doc="Taproot-tagged hash for the taproot signature hash", true
);

#[cfg(test)]
mod test {
    use super::*;
    use hashes::hex::ToHex;
    use hashes::sha256t::Tag;
    use hashes::{sha256, Hash, HashEngine};

    fn tag_engine(tag_name: &str) -> sha256::HashEngine {
        let mut engine = sha256::Hash::engine();
        let tag_hash = sha256::Hash::hash(tag_name.as_bytes());
        engine.input(&tag_hash[..]);
        engine.input(&tag_hash[..]);
        engine
    }

    #[test]
    fn test_midstates() {
        // check midstate against hard-coded values
        assert_eq!(MIDSTATE_TAPLEAF, tag_engine("TapLeaf").midstate().into_inner());
        assert_eq!(MIDSTATE_TAPBRANCH, tag_engine("TapBranch").midstate().into_inner());
        assert_eq!(MIDSTATE_TAPTWEAK, tag_engine("TapTweak").midstate().into_inner());
        assert_eq!(MIDSTATE_TAPSIGHASH, tag_engine("TapSighash").midstate().into_inner());

        // test that engine creation roundtrips
        assert_eq!(tag_engine("TapLeaf").midstate(), TapLeafTag::engine().midstate());
        assert_eq!(tag_engine("TapBranch").midstate(), TapBranchTag::engine().midstate());
        assert_eq!(tag_engine("TapTweak").midstate(), TapTweakTag::engine().midstate());
        assert_eq!(tag_engine("TapSighash").midstate(), TapSighashTag::engine().midstate());

        // check that hash creation is the same as building into the same engine
        fn empty_hash(tag_name: &str) -> [u8; 32] {
            let mut e = tag_engine(tag_name);
            e.input(&[]);
            sha256::Hash::from_engine(e).into_inner()
        }
        assert_eq!(empty_hash("TapLeaf"), TapLeafHash::hash(&[]).into_inner());
        assert_eq!(empty_hash("TapBranch"), TapBranchHash::hash(&[]).into_inner());
        assert_eq!(empty_hash("TapTweak"), TapTweakHash::hash(&[]).into_inner());
        assert_eq!(empty_hash("TapSighash"), TapSighashHash::hash(&[]).into_inner());
    }

    #[test]
    fn test_vectors_core() {
        //! Test vectors taken from Core

        // uninitialized writers
        //   CHashWriter writer = HasherTapLeaf;
        //   writer.GetSHA256().GetHex()
        assert_eq!(
            TapLeafHash::from_engine(TapLeafTag::engine()).to_hex(),
            "cbfa0621df37662ca57697e5847b6abaf92934a1a5624916f8d177a388c21252"
        );
        assert_eq!(
            TapBranchHash::from_engine(TapBranchTag::engine()).to_hex(),
            "dffd9fbe4c21c893fa934f8774eda0e1efdc06f52ffbf5c1533c6f4dec73c353"
        );
        assert_eq!(
            TapTweakHash::from_engine(TapTweakTag::engine()).to_hex(),
            "e4156b45ff9b277dd92a042af9eed8c91f1d037f68f0d6b20001ab749422a48a"
        );
        assert_eq!(
            TapSighashHash::from_engine(TapSighashTag::engine()).to_hex(),
            "03c8b9d47cdb5f7bf924e282ce99ba8d2fe581262a04002907d8bc4a9111bcda"
        );

        // 0-byte
        //   CHashWriter writer = HasherTapLeaf;
        //   writer << std::vector<unsigned char>{};
        //   writer.GetSHA256().GetHex()
        // Note that Core writes the 0 length prefix when an empty vector is written.
        assert_eq!(
            TapLeafHash::hash(&[0]).to_hex(),
            "29589d5122ec666ab5b4695070b6debc63881a4f85d88d93ddc90078038213ed"
        );
        assert_eq!(
            TapBranchHash::hash(&[0]).to_hex(),
            "1deb45569eb6b2da88b5c2ab46d6a64ab08d58a2fdd5f75a24e6c760194b5392"
        );
        assert_eq!(
            TapTweakHash::hash(&[0]).to_hex(),
            "1eea90d42a359c89bbf702ddf6bde140349e95b9e8036ff1c37f04e6b53787cd"
        );
        assert_eq!(
            TapSighashHash::hash(&[0]).to_hex(),
            "cd10c023c300fb9a507dff136370fba1d8a0566667cfafc4099a8803e00dfdc2"
        );
    }
}