Implement Witness commitment check for Block. Remove MerkleRoot imple…

…mentations for types implementing BitcoinHash as

it is misleading. MerkleRoot is defined instead for a Block.

src/blockdata/block.rs

@@ -24,12 +24,13 @@ use bitcoin_hashes::{sha256d, Hash};
 
 use util;
 use util::Error::{SpvBadTarget, SpvBadProofOfWork};
-use util::hash::BitcoinHash;
+use util::hash::{BitcoinHash, MerkleRoot, bitcoin_merkle_root};
 use util::uint::Uint256;
-use consensus::encode::VarInt;
+use consensus::encode::{VarInt, Encodable};
 use network::constants::Network;
 use blockdata::transaction::Transaction;
 use blockdata::constants::max_target;
+use bitcoin_hashes::HashEngine;
 
 /// A block header, which contains all the block's information except
 /// the actual transactions
@@ -60,6 +61,61 @@ pub struct Block {
     pub txdata: Vec<Transaction>
 }
 
+impl Block {
+    /// check if merkle root of header matches merkle root of the transaction list
+    pub fn check_merkle_root (&self) -> bool {
+        self.header.merkle_root == self.merkle_root()
+    }
+
+    /// check if witness commitment in coinbase is matching the transaction list
+    pub fn check_witness_commitment(&self) -> bool {
+
+        // witness commitment is optional if there are no transactions using SegWit in the block
+        if self.txdata.iter().all(|t| t.input.iter().all(|i| i.witness.is_empty())) {
+            return true;
+        }
+        if self.txdata.len() > 0 {
+            let coinbase = &self.txdata[0];
+            if coinbase.is_coin_base() {
+                // commitment is in the last output that starts with below magic
+                if let Some(pos) = coinbase.output.iter()
+                    .rposition(|o| {
+                        o.script_pubkey.len () >= 38 &&
+                        o.script_pubkey[0..6] == [0x6a, 0x24, 0xaa, 0x21, 0xa9, 0xed] }) {
+                    let commitment = sha256d::Hash::from_slice(&coinbase.output[pos].script_pubkey.as_bytes()[6..38]).unwrap();
+                    // witness reserved value is in coinbase input witness
+                    if coinbase.input[0].witness.len() == 1 && coinbase.input[0].witness[0].len() == 32 {
+                        let witness_root = self.witness_root();
+                        return commitment == Self::compute_witness_commitment(&witness_root, coinbase.input[0].witness[0].as_slice())
+                    }
+                }
+            }
+        }
+        false
+    }
+
+    /// compute witness commitment for the transaction list
+    pub fn compute_witness_commitment (witness_root: &sha256d::Hash, witness_reserved_value: &[u8]) -> sha256d::Hash {
+        let mut encoder = sha256d::Hash::engine();
+        witness_root.consensus_encode(&mut encoder).unwrap();
+        encoder.input(witness_reserved_value);
+        sha256d::Hash::from_engine(encoder)
+    }
+
+    /// Merkle root of transactions hashed for witness
+    pub fn witness_root(&self) -> sha256d::Hash {
+        let mut txhashes = vec!(sha256d::Hash::default());
+        txhashes.extend(self.txdata.iter().skip(1).map(|t|t.bitcoin_hash()));
+        bitcoin_merkle_root(txhashes)
+    }
+}
+
+impl MerkleRoot for Block {
+    fn merkle_root(&self) -> sha256d::Hash {
+        bitcoin_merkle_root(self.txdata.iter().map(|obj| obj.txid()).collect())
+    }
+}
+
 /// A block header with txcount attached, which is given in the `headers`
 /// network message.
 #[derive(PartialEq, Eq, Clone, Debug)]
@@ -170,6 +226,7 @@ mod tests {
 
     use blockdata::block::{Block, BlockHeader};
     use consensus::encode::{deserialize, serialize};
+    use util::hash::MerkleRoot;
 
     #[test]
     fn block_test() {
@@ -187,13 +244,16 @@ mod tests {
         let real_decode = decode.unwrap();
         assert_eq!(real_decode.header.version, 1);
         assert_eq!(serialize(&real_decode.header.prev_blockhash), prevhash);
-        // [test] TODO: actually compute the merkle root
+        assert_eq!(real_decode.header.merkle_root, real_decode.merkle_root());
         assert_eq!(serialize(&real_decode.header.merkle_root), merkle);
         assert_eq!(real_decode.header.time, 1231965655);
         assert_eq!(real_decode.header.bits, 486604799);
         assert_eq!(real_decode.header.nonce, 2067413810);
         // [test] TODO: check the transaction data
-
+
+        // should be also ok for a non-witness block as commitment is optional in that case
+        assert!(real_decode.check_witness_commitment());
+
         assert_eq!(serialize(&real_decode), some_block);
     }
 
@@ -212,11 +272,14 @@ mod tests {
         assert_eq!(real_decode.header.version, 0x20000000);  // VERSIONBITS but no bits set
         assert_eq!(serialize(&real_decode.header.prev_blockhash), prevhash);
         assert_eq!(serialize(&real_decode.header.merkle_root), merkle);
+        assert_eq!(real_decode.header.merkle_root, real_decode.merkle_root());
         assert_eq!(real_decode.header.time, 1472004949);
         assert_eq!(real_decode.header.bits, 0x1a06d450);
         assert_eq!(real_decode.header.nonce, 1879759182);
         // [test] TODO: check the transaction data
 
+        assert!(real_decode.check_witness_commitment());
+
         assert_eq!(serialize(&real_decode), segwit_block);
     }
 

src/blockdata/constants.rs

@@ -27,7 +27,6 @@ use blockdata::transaction::{OutPoint, Transaction, TxOut, TxIn};
 use blockdata::block::{Block, BlockHeader};
 use network::constants::Network;
 use util::misc::hex_bytes;
-use util::hash::MerkleRoot;
 use util::uint::Uint256;
 
 /// The maximum allowable sequence number
@@ -98,7 +97,7 @@ pub fn genesis_block(network: Network) -> Block {
                 header: BlockHeader {
                     version: 1,
                     prev_blockhash: Default::default(),
-                    merkle_root: txdata.merkle_root(),
+                    merkle_root: txdata[0].txid(),
                     time: 1231006505,
                     bits: 0x1d00ffff,
                     nonce: 2083236893
@@ -112,7 +111,7 @@ pub fn genesis_block(network: Network) -> Block {
                 header: BlockHeader {
                     version: 1,
                     prev_blockhash: Default::default(),
-                    merkle_root: txdata.merkle_root(),
+                    merkle_root: txdata[0].txid(),
                     time: 1296688602,
                     bits: 0x1d00ffff,
                     nonce: 414098458
@@ -126,7 +125,7 @@ pub fn genesis_block(network: Network) -> Block {
                 header: BlockHeader {
                     version: 1,
                     prev_blockhash: Default::default(),
-                    merkle_root: txdata.merkle_root(),
+                    merkle_root: txdata[0].txid(),
                     time: 1296688602,
                     bits: 0x207fffff,
                     nonce: 2

src/util/hash.rs

@@ -51,18 +51,6 @@ pub fn bitcoin_merkle_root(data: Vec<sha256d::Hash>) -> sha256d::Hash {
     bitcoin_merkle_root(next)
 }
 
-impl<'a, T: BitcoinHash> MerkleRoot for &'a [T] {
-    fn merkle_root(&self) -> sha256d::Hash {
-        bitcoin_merkle_root(self.iter().map(|obj| obj.bitcoin_hash()).collect())
-    }
-}
-
-impl <T: BitcoinHash> MerkleRoot for Vec<T> {
-    fn merkle_root(&self) -> sha256d::Hash {
-        (&self[..]).merkle_root()
-    }
-}
-
 /// Objects which are referred to by hash
 pub trait BitcoinHash {
     /// Produces a Sha256dHash which can be used to refer to the object