ElementsProject · apoelstra · Sep 20, 2019 · Apr 29, 2019 · Apr 28, 2019 · Apr 29, 2019
diff --git a/src/fast_merkle_root.rs b/src/fast_merkle_root.rs
@@ -0,0 +1,123 @@
+// Rust Elements Library
+// Written in 2019 by
+//   The Elements 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/>.
+//
+
+use bitcoin::hashes::{sha256, Hash, HashEngine};
+
+/// Calculate a single sha256 midstate hash of the given left and right leaves.
+#[inline]
+fn sha256midstate(left: &[u8], right: &[u8]) -> sha256::Midstate {
+    let mut engine = sha256::Hash::engine();
+    engine.input(left);
+    engine.input(right);
+    engine.midstate()
+}
+
+/// Compute the Merkle root of the give hashes using mid-state only.
+/// The inputs must be byte slices of length 32.
+/// Note that the merkle root calculated with this method is not the same as the
+/// one computed by a normal SHA256(d) merkle root.
+pub fn fast_merkle_root(leaves: &[[u8; 32]]) -> sha256::Midstate {
+    let mut result_hash = Default::default();
+    // Implementation based on ComputeFastMerkleRoot method in Elements Core.
+    if leaves.is_empty() {
+        return result_hash;
+    }
+
+    // inner is an array of eagerly computed subtree hashes, indexed by tree
+    // level (0 being the leaves).
+    // For example, when count is 25 (11001 in binary), inner[4] is the hash of
+    // the first 16 leaves, inner[3] of the next 8 leaves, and inner[0] equal to
+    // the last leaf. The other inner entries are undefined.
+    //
+    // First process all leaves into 'inner' values.
+    let mut inner: [sha256::Midstate; 32] = Default::default();
+    let mut count: u32 = 0;
+    while (count as usize) < leaves.len() {
+        let mut temp_hash = sha256::Midstate::from_inner(leaves[count as usize]);
+        count += 1;
+        // For each of the lower bits in count that are 0, do 1 step. Each
+        // corresponds to an inner value that existed before processing the
+        // current leaf, and each needs a hash to combine it.
+        let mut level = 0;
+        while count & (1u32 << level) == 0 {
+            temp_hash = sha256midstate(&inner[level][..], &temp_hash[..]);
+            level += 1;
+        }
+        // Store the resulting hash at inner position level.
+        inner[level] = temp_hash;
+    }
+
+    // Do a final 'sweep' over the rightmost branch of the tree to process
+    // odd levels, and reduce everything to a single top value.
+    // Level is the level (counted from the bottom) up to which we've sweeped.
+    //
+    // As long as bit number level in count is zero, skip it. It means there
+    // is nothing left at this level.
+    let mut level = 0;
+    while count & (1u32 << level) == 0 {
+        level += 1;
+    }
+    result_hash = inner[level];
+
+    while count != (1u32 << level) {
+        // If we reach this point, hash is an inner value that is not the top.
+        // We combine it with itself (Bitcoin's special rule for odd levels in
+        // the tree) to produce a higher level one.
+
+        // Increment count to the value it would have if two entries at this
+        // level had existed and propagate the result upwards accordingly.
+        count += 1 << level;
+        level += 1;
+        while count & (1u32 << level) == 0 {
+            result_hash = sha256midstate(&inner[level][..], &result_hash[..]);
+            level += 1;
+        }
+    }
+    // Return result.
+    result_hash
+}
+
+#[cfg(test)]
+mod tests {
+    use super::fast_merkle_root;
+    use bitcoin::hashes::hex::FromHex;
+    use bitcoin::hashes::sha256;
+
+    #[test]
+    fn test_fast_merkle_root() {
+        // unit test vectors from Elements Core
+        let test_leaves = [
+            "b66b041650db0f297b53f8d93c0e8706925bf3323f8c59c14a6fac37bfdcd06f",
+            "99cb2fa68b2294ae133550a9f765fc755d71baa7b24389fed67d1ef3e5cb0255",
+            "257e1b2fa49dd15724c67bac4df7911d44f6689860aa9f65a881ae0a2f40a303",
+            "b67b0b9f093fa83d5e44b707ab962502b7ac58630e556951136196e65483bb80",
+        ];
+
+        let test_roots = [
+            "0000000000000000000000000000000000000000000000000000000000000000",
+            "b66b041650db0f297b53f8d93c0e8706925bf3323f8c59c14a6fac37bfdcd06f",
+            "f752938da0cb71c051aabdd5a86658e8d0b7ac00e1c2074202d8d2a79d8a6cf6",
+            "245d364a28e9ad20d522c4a25ffc6a7369ab182f884e1c7dcd01aa3d32896bd3",
+            "317d6498574b6ca75ee0368ec3faec75e096e245bdd5f36e8726fa693f775dfc",
+        ];
+
+        let mut leaves = vec![];
+        for i in 0..4 {
+            let root = fast_merkle_root(&leaves);
+            assert_eq!(root, FromHex::from_hex(&test_roots[i]).unwrap(), "root #{}", i);
+            leaves.push(sha256::Midstate::from_hex(&test_leaves[i]).unwrap().into_inner());
+        }
+        assert_eq!(fast_merkle_root(&leaves), FromHex::from_hex(test_roots[4]).unwrap());
+    }
+}
diff --git a/src/issuance.rs b/src/issuance.rs
@@ -0,0 +1,214 @@
+// Rust Elements Library
+// Written in 2019 by
+//   The Elements 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/>.
+//
+
+//! Asset Issuance
+
+use bitcoin::util::hash::BitcoinHash;
+use bitcoin::hashes::{hex, sha256, Hash};
+use fast_merkle_root::fast_merkle_root;
+use transaction::OutPoint;
+
+/// The zero hash.
+const ZERO32: [u8; 32] = [
+    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+];
+/// The one hash.
+const ONE32: [u8; 32] = [
+    1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+];
+/// The two hash.
+const TWO32: [u8; 32] = [
+    2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+];
+
+/// An issued asset ID.
+#[derive(Copy, Clone, PartialEq, Eq, Default, PartialOrd, Ord, Hash)]
+pub struct AssetId(sha256::Midstate);
+
+impl AssetId {
+    /// Create an [AssetId] from its inner type.
+    pub fn from_inner(midstate: sha256::Midstate) -> AssetId {
+        AssetId(midstate)
+    }
+
+    /// Convert the [AssetId] into its inner type.
+    pub fn into_inner(self) -> sha256::Midstate {
+        self.0
+    }
+
+    /// Generate the asset entropy from the issuance prevout and the contract hash.
+    pub fn generate_asset_entropy(
+        prevout: OutPoint,
+        contract_hash: sha256::Hash,
+    ) -> sha256::Midstate {
+        // E : entropy
+        // I : prevout
+        // C : contract
+        // E = H( H(I) || H(C) )
+        fast_merkle_root(&[prevout.bitcoin_hash().into_inner(), contract_hash.into_inner()])
+    }
+
+    /// Calculate the asset ID from the asset entropy.
+    pub fn from_entropy(entropy: sha256::Midstate) -> AssetId {
+        // H_a : asset tag
+        // E   : entropy
+        // H_a = H( E || 0 )
+        AssetId(fast_merkle_root(&[entropy.into_inner(), ZERO32]))
+    }
+
+    /// Calculate the reissuance token asset ID from the asset entropy.
+    pub fn reissuance_token_from_entropy(entropy: sha256::Midstate, confidential: bool) -> AssetId {
+        // H_a : asset reissuance tag
+        // E   : entropy
+        // if not fConfidential:
+        //     H_a = H( E || 1 )
+        // else
+        //     H_a = H( E || 2 )
+        let second = match confidential {
+            false => ONE32,
+            true => TWO32,
+        };
+        AssetId(fast_merkle_root(&[entropy.into_inner(), second]))
+    }
+}
+
+impl hex::FromHex for AssetId {
+    fn from_byte_iter<I>(iter: I) -> Result<Self, hex::Error>
+    where
+        I: Iterator<Item = Result<u8, hex::Error>> + ExactSizeIterator + DoubleEndedIterator,
+    {
+        sha256::Midstate::from_byte_iter(iter).map(AssetId)
+    }
+}
+
+impl ::std::fmt::Display for AssetId {
+    fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
+        ::std::fmt::Display::fmt(&self.0, f)
+    }
+}
+
+impl ::std::fmt::Debug for AssetId {
+    fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
+        ::std::fmt::Display::fmt(&self, f)
+    }
+}
+
+impl ::std::fmt::LowerHex for AssetId {
+    fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
+        ::std::fmt::LowerHex::fmt(&self.0, f)
+    }
+}
+
+#[cfg(feature = "serde")]
+impl ::serde::Serialize for AssetId {
+    fn serialize<S: ::serde::Serializer>(&self, s: S) -> Result<S::Ok, S::Error> {
+        use bitcoin::hashes::hex::ToHex;
+        if s.is_human_readable() {
+            s.serialize_str(&self.to_hex())
+        } else {
+            s.serialize_bytes(&self.0[..])
+        }
+    }
+}
+
+#[cfg(feature = "serde")]
+impl<'de> ::serde::Deserialize<'de> for AssetId {
+    fn deserialize<D: ::serde::Deserializer<'de>>(d: D) -> Result<AssetId, D::Error> {
+        use bitcoin::hashes::hex::FromHex;
+
+        if d.is_human_readable() {
+            struct HexVisitor;
+
+            impl<'de> ::serde::de::Visitor<'de> for HexVisitor {
+                type Value = AssetId;
+
+                fn expecting(&self, formatter: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
+                    formatter.write_str("an ASCII hex string")
+                }
+
+                fn visit_bytes<E>(self, v: &[u8]) -> Result<Self::Value, E>
+                where
+                    E: ::serde::de::Error,
+                {
+                    if let Ok(hex) = ::std::str::from_utf8(v) {
+                        AssetId::from_hex(hex).map_err(E::custom)
+                    } else {
+                        return Err(E::invalid_value(::serde::de::Unexpected::Bytes(v), &self));
+                    }
+                }
+
+                fn visit_str<E>(self, v: &str) -> Result<Self::Value, E>
+                where
+                    E: ::serde::de::Error,
+                {
+                    AssetId::from_hex(v).map_err(E::custom)
+                }
+            }
+
+            d.deserialize_str(HexVisitor)
+        } else {
+            struct BytesVisitor;
+
+            impl<'de> ::serde::de::Visitor<'de> for BytesVisitor {
+                type Value = AssetId;
+
+                fn expecting(&self, formatter: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
+                    formatter.write_str("a bytestring")
+                }
+
+                fn visit_bytes<E>(self, v: &[u8]) -> Result<Self::Value, E>
+                where
+                    E: ::serde::de::Error,
+                {
+                    if v.len() != 32 {
+                        Err(E::invalid_length(v.len(), &stringify!($len)))
+                    } else {
+                        let mut ret = [0; 32];
+                        ret.copy_from_slice(v);
+                        Ok(AssetId(sha256::Midstate::from_inner(ret)))
+                    }
+                }
+            }
+
+            d.deserialize_bytes(BytesVisitor)
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use std::str::FromStr;
+
+    use bitcoin::hashes::hex::FromHex;
+    use bitcoin::hashes::sha256;
+
+    #[test]
+    fn example_elements_core() {
+        // example test data from Elements Core 0.17
+        let prevout_str = "05a047c98e82a848dee94efcf32462b065198bebf2404d201ba2e06db30b28f4:0";
+        let entropy_hex = "746f447f691323502cad2ef646f932613d37a83aeaa2133185b316648df4b70a";
+        let asset_id_hex = "dcd60818d863b5c026c40b2bc3ba6fdaf5018bcc8606c18adf7db4da0bcd8533";
+        let token_id_hex = "c1adb114f4f87d33bf9ce90dd4f9ca523dd414d6cd010a7917903e2009689530";
+
+        let contract_hash = sha256::Hash::from_inner(ZERO32);
+        let prevout = OutPoint::from_str(prevout_str).unwrap();
+        let entropy = sha256::Midstate::from_hex(entropy_hex).unwrap();
+        assert_eq!(AssetId::generate_asset_entropy(prevout, contract_hash), entropy);
+        let asset_id = AssetId::from_hex(asset_id_hex).unwrap();
+        assert_eq!(AssetId::from_entropy(entropy), asset_id);
+        let token_id = AssetId::from_hex(token_id_hex).unwrap();
+        assert_eq!(AssetId::reissuance_token_from_entropy(entropy, false), token_id);
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
@@ -38,6 +38,8 @@ mod block;
 pub mod confidential;
 pub mod dynafed;
 pub mod encode;
+mod fast_merkle_root;
+pub mod issuance;
 mod transaction;
 
 // export everything at the top level so it can be used as `elements::Transaction` etc.
@@ -46,4 +48,6 @@ pub use transaction::{OutPoint, PeginData, PegoutData, TxIn, TxOut, TxInWitness,
 pub use block::{BlockHeader, Block};
 pub use block::ExtData as BlockExtData;
 pub use ::bitcoin::consensus::encode::VarInt;
+pub use fast_merkle_root::fast_merkle_root;
+pub use issuance::AssetId;