Merge pull request #677 from sanket1729/taptree_utils

Add taproot data structures

src/lib.rs

@@ -178,10 +178,10 @@ mod prelude {
     pub use std::{string::{String, ToString}, vec::Vec, boxed::Box, borrow::{Cow, ToOwned}, slice, rc, sync};
 
     #[cfg(all(not(feature = "std"), not(test)))]
-    pub use alloc::collections::{BTreeMap, btree_map};
+    pub use alloc::collections::{BTreeMap, BTreeSet, btree_map, BinaryHeap};
 
     #[cfg(any(feature = "std", test))]
-    pub use std::collections::{BTreeMap, btree_map};
+    pub use std::collections::{BTreeMap, BTreeSet, btree_map, BinaryHeap};
 
     #[cfg(feature = "std")]
     pub use std::io::sink;

src/util/sighash.rs

@@ -31,6 +31,8 @@ use {Script, Transaction, TxOut};
 
 use prelude::*;
 
+use super::taproot::LeafVersion;
+
 /// Efficiently calculates signature hash message for legacy, segwit and taproot inputs.
 #[derive(Debug)]
 pub struct SigHashCache<T: Deref<Target = Transaction>> {
@@ -88,7 +90,6 @@ pub enum Prevouts<'u> {
     All(&'u [TxOut]),
 }
 
-const LEAF_VERSION_TAPSCRIPT: u8 = 0xc0;
 const KEY_VERSION_0: u8 = 0u8;
 
 /// Information related to the script path spending
@@ -96,7 +97,7 @@ const KEY_VERSION_0: u8 = 0u8;
 pub struct ScriptPath<'s> {
     script: &'s Script,
     code_separator_pos: u32,
-    leaf_version: u8,
+    leaf_version: LeafVersion,
 }
 
 /// Hashtype of an input's signature, encoded in the last byte of the signature
@@ -214,7 +215,7 @@ impl<'u> Prevouts<'u> {
 
 impl<'s> ScriptPath<'s> {
     /// Create a new ScriptPath structure
-    pub fn new(script: &'s Script, code_separator_pos: u32, leaf_version: u8) -> Self {
+    pub fn new(script: &'s Script, code_separator_pos: u32, leaf_version: LeafVersion) -> Self {
         ScriptPath {
             script,
             code_separator_pos,
@@ -223,7 +224,7 @@ impl<'s> ScriptPath<'s> {
     }
     /// Create a new ScriptPath structure using default values for `code_separator_pos` and `leaf_version`
     pub fn with_defaults(script: &'s Script) -> Self {
-        Self::new(script, 0xFFFFFFFFu32, LEAF_VERSION_TAPSCRIPT)
+        Self::new(script, 0xFFFFFFFFu32, LeafVersion::default())
     }
 }
 
@@ -399,7 +400,7 @@ impl<R: Deref<Target = Transaction>> SigHashCache<R> {
         }) = script_path
         {
             let mut enc = TapLeafHash::engine();
-            leaf_version.consensus_encode(&mut enc)?;
+            leaf_version.as_u8().consensus_encode(&mut enc)?;
             script.consensus_encode(&mut enc)?;
             let hash = TapLeafHash::from_engine(enc);
 

src/util/taproot.rs

@@ -13,8 +13,19 @@
 
 //! Taproot
 //!
+use prelude::*;
+use io;
+use secp256k1::{self, Secp256k1};
 
-use hashes::{sha256, sha256t, Hash};
+use core::fmt;
+#[cfg(feature = "std")]
+use std::error;
+
+use hashes::{sha256, sha256t, Hash, HashEngine};
+use schnorr;
+use Script;
+
+use consensus::Encodable;
 
 /// The SHA-256 midstate value for the TapLeaf hash.
 const MIDSTATE_TAPLEAF: [u8; 32] = [
@@ -82,12 +93,812 @@ sha256t_hash_newtype!(TapSighashHash, TapSighashTag, MIDSTATE_TAPSIGHASH, 64,
     doc="Taproot-tagged hash for the taproot signature hash", true
 );
 
+impl TapTweakHash {
+
+    /// Create a new BIP341 [`TapTweakHash`] from key and tweak
+    /// Produces H_taptweak(P||R) where P is internal key and R is the merkle root
+    pub fn from_key_and_tweak(
+        internal_key: schnorr::PublicKey,
+        merkle_root: Option<TapBranchHash>,
+    ) -> TapTweakHash {
+        let mut eng = TapTweakHash::engine();
+        // always hash the key
+        eng.input(&internal_key.serialize());
+        if let Some(h) = merkle_root {
+            eng.input(&h);
+        } else {
+            // nothing to hash
+        }
+        TapTweakHash::from_engine(eng)
+    }
+}
+
+impl TapLeafHash {
+    /// function to compute leaf hash from components
+    pub fn from_script(script: &Script, ver: LeafVersion) -> TapLeafHash {
+        let mut eng = TapLeafHash::engine();
+        ver.as_u8()
+            .consensus_encode(&mut eng)
+            .expect("engines don't err");
+        script
+            .consensus_encode(&mut eng)
+            .expect("engines don't err");
+        TapLeafHash::from_engine(eng)
+    }
+}
+
+/// Maximum depth of a Taproot Tree Script spend path
+// https://github.com/bitcoin/bitcoin/blob/e826b22da252e0599c61d21c98ff89f366b3120f/src/script/interpreter.h#L229
+pub const TAPROOT_CONTROL_MAX_NODE_COUNT: usize = 128;
+/// Size of a taproot control node
+// https://github.com/bitcoin/bitcoin/blob/e826b22da252e0599c61d21c98ff89f366b3120f/src/script/interpreter.h#L228
+pub const TAPROOT_CONTROL_NODE_SIZE: usize = 32;
+/// Tapleaf mask for getting the leaf version from first byte of control block
+// https://github.com/bitcoin/bitcoin/blob/e826b22da252e0599c61d21c98ff89f366b3120f/src/script/interpreter.h#L225
+pub const TAPROOT_LEAF_MASK: u8 = 0xfe;
+/// Tapscript leaf version
+// https://github.com/bitcoin/bitcoin/blob/e826b22da252e0599c61d21c98ff89f366b3120f/src/script/interpreter.h#L226
+pub const TAPROOT_LEAF_TAPSCRIPT: u8 = 0xc0;
+/// Tapscript control base size
+// https://github.com/bitcoin/bitcoin/blob/e826b22da252e0599c61d21c98ff89f366b3120f/src/script/interpreter.h#L227
+pub const TAPROOT_CONTROL_BASE_SIZE: usize = 33;
+/// Tapscript control max size
+// https://github.com/bitcoin/bitcoin/blob/e826b22da252e0599c61d21c98ff89f366b3120f/src/script/interpreter.h#L230
+pub const TAPROOT_CONTROL_MAX_SIZE: usize =
+    TAPROOT_CONTROL_BASE_SIZE + TAPROOT_CONTROL_NODE_SIZE * TAPROOT_CONTROL_MAX_NODE_COUNT;
+
+// type alias for versioned tap script corresponding merkle proof
+type ScriptMerkleProofMap = BTreeMap<(Script, LeafVersion), BTreeSet<TaprootMerkleBranch>>;
+/// Data structure for representing Taproot spending information.
+/// Taproot output corresponds to a combination of a
+/// single public key condition (known the internal key), and zero or more
+/// general conditions encoded in scripts organized in the form of a binary tree.
+///
+/// Taproot can be spent be either:
+/// - Spending using the key path i.e., with secret key corresponding to the output_key
+/// - By satisfying any of the scripts in the script spent path. Each script can be satisfied by providing
+///   a witness stack consisting of the script's inputs, plus the script itself and the control block.
+///
+/// If one or more of the spending conditions consist of just a single key (after aggregation),
+/// the most likely one should be made the internal key.
+/// See [BIP341](https://github.com/bitcoin/bips/blob/master/bip-0341.mediawiki) for more details
+/// on choosing internal keys for a taproot application
+///
+/// Note: This library currently does not support [annex](https://github.com/bitcoin/bips/blob/master/bip-0341.mediawiki#cite_note-5)
+#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct TaprootSpendInfo {
+    /// The BIP341 internal key.
+    internal_key: schnorr::PublicKey,
+    /// The Merkle root of the script tree (None if there are no scripts)
+    merkle_root: Option<TapBranchHash>,
+    /// The sign final output pubkey as per BIP 341
+    output_key_parity: bool,
+    /// The tweaked output key
+    output_key: schnorr::PublicKey,
+    /// Map from (script, leaf_version) to (sets of) [`TaprootMerkleBranch`].
+    /// More than one control block for a given script is only possible if it
+    /// appears in multiple branches of the tree. In all cases, keeping one should
+    /// be enough for spending funds, but we keep all of the paths so that
+    /// a full tree can be constructed again from spending data if required.
+    script_map: ScriptMerkleProofMap,
+}
+
+impl TaprootSpendInfo {
+    /// Create a new [`TaprootSpendInfo`] from a list of script(with default script version) and
+    /// weights of satisfaction for that script. The weights represent the probability of
+    /// each branch being taken. If probabilities/weights for each condition are known,
+    /// constructing the tree as a Huffman tree is the optimal way to minimize average
+    /// case satisfaction cost. This function takes input an iterator of tuple(u64, &Script)
+    /// where usize represents the satisfaction weights of the branch.
+    /// For example, [(3, S1), (2, S2), (5, S3)] would construct a TapTree that has optimal
+    /// satisfaction weight when probability for S1 is 30%, S2 is 20% and S3 is 50%.
+    ///
+    /// # Errors:
+    ///
+    /// - When the optimal huffman tree has a depth more than 128
+    /// - If the provided list of script weights is empty
+    /// - If the script weight calculations overflow. This should not happen unless you are
+    /// dealing with numbers close to 2^64.
+    pub fn with_huffman_tree<C, I>(
+        secp: &Secp256k1<C>,
+        internal_key: schnorr::PublicKey,
+        script_weights: I,
+    ) -> Result<Self, TaprootBuilderError>
+    where
+        I: IntoIterator<Item = (u64, Script)>,
+        C: secp256k1::Verification,
+    {
+        let mut node_weights = BinaryHeap::<(u64, NodeInfo)>::new();
+        for (p, leaf) in script_weights {
+            node_weights.push((p, NodeInfo::new_leaf_with_ver(leaf, LeafVersion::default())));
+        }
+        if node_weights.is_empty() {
+            return Err(TaprootBuilderError::IncompleteTree);
+        }
+        while node_weights.len() > 1 {
+            // Combine the last two elements and insert a new node
+            let (p1, s1) = node_weights.pop().expect("len must be at least two");
+            let (p2, s2) = node_weights.pop().expect("len must be at least two");
+            // Insert the sum of first two in the tree as a new node
+            let p = p1.checked_add(p2).ok_or(TaprootBuilderError::ScriptWeightOverflow)?;
+            node_weights.push((p, NodeInfo::combine(s1, s2)?));
+        }
+        // Every iteration of the loop reduces the node_weights.len() by exactly 1
+        // Therefore, the loop will eventually terminate with exactly 1 element
+        debug_assert!(node_weights.len() == 1);
+        let node = node_weights.pop().expect("huffman tree algorithm is broken").1;
+        return Ok(Self::from_node_info(secp, internal_key, node));
+    }
+
+    /// Create a new key spend with internal key and proided merkle root.
+    /// Provide [`None`] for merkle_root if there is no script path.
+    ///
+    /// *Note*: As per BIP341
+    ///
+    /// When the merkle root is [`None`], the output key commits to an unspendable
+    /// script path instead of having no script path. This is achieved by computing
+    /// the output key point as Q = P + int(hashTapTweak(bytes(P)))G.
+    /// See also [`TaprootSpendInfo::tap_tweak`].
+    /// Refer to BIP 341 footnote (Why should the output key always have
+    /// a taproot commitment, even if there is no script path?) for more details
+    ///
+    pub fn new_key_spend<C: secp256k1::Verification>(
+        secp: &Secp256k1<C>,
+        internal_key: schnorr::PublicKey,
+        merkle_root: Option<TapBranchHash>,
+    ) -> Self {
+        let tweak = TapTweakHash::from_key_and_tweak(internal_key, merkle_root);
+        let mut output_key = internal_key;
+        // # Panics:
+        //
+        // This would return Err if the merkle root hash is the negation of the secret
+        // key corresponding to the internal key.
+        // Because the tweak is derived as specified in BIP341 (hash output of a function),
+        // this is unlikely to occur (1/2^128) in real life usage, it is safe to unwrap this
+        let parity = output_key
+            .tweak_add_assign(&secp, &tweak)
+            .expect("TapTweakHash::from_key_and_tweak is broken");
+        Self {
+            internal_key: internal_key,
+            merkle_root: merkle_root,
+            output_key_parity: parity,
+            output_key: output_key,
+            script_map: BTreeMap::new(),
+        }
+    }
+
+    /// Obtain the tweak and parity used to compute the output_key
+    pub fn tap_tweak(&self) -> TapTweakHash {
+        TapTweakHash::from_key_and_tweak(self.internal_key, self.merkle_root)
+    }
+
+    /// Obtain the internal key
+    pub fn internal_key(&self) -> schnorr::PublicKey {
+        self.internal_key
+    }
+
+    /// Obtain the merkle root
+    pub fn merkle_root(&self) -> Option<TapBranchHash> {
+        self.merkle_root
+    }
+
+    /// Output key(the key used in script pubkey) from Spend data. See also
+    /// [`TaprootSpendInfo::output_key_parity`]
+    pub fn output_key(&self) -> schnorr::PublicKey {
+        self.output_key
+    }
+
+    /// Parity of the output key. See also [`TaprootSpendInfo::output_key`]
+    pub fn output_key_parity(&self) -> bool {
+        self.output_key_parity
+    }
+
+    // Internal function to compute [`TaprootSpendInfo`] from NodeInfo
+    fn from_node_info<C: secp256k1::Verification>(
+        secp: &Secp256k1<C>,
+        internal_key: schnorr::PublicKey,
+        node: NodeInfo,
+    ) -> TaprootSpendInfo {
+        // Create as if it is a key spend path with the given merkle root
+        let root_hash = Some(TapBranchHash::from_inner(node.hash.into_inner()));
+        let mut info = TaprootSpendInfo::new_key_spend(secp, internal_key, root_hash);
+        for leaves in node.leaves {
+            let key = (leaves.script, leaves.ver);
+            let value = leaves.merkle_branch;
+            match info.script_map.get_mut(&key) {
+                Some(set) => {
+                    set.insert(value);
+                    continue; // NLL fix
+                }
+                None => {}
+            }
+            let mut set = BTreeSet::new();
+            set.insert(value);
+            info.script_map.insert(key, set);
+        }
+        info
+    }
+
+    /// Access the internal script map
+    pub fn as_script_map(&self) -> &ScriptMerkleProofMap {
+        &self.script_map
+    }
+
+    /// Obtain a [`ControlBlock`] for particular script with the given version.
+    /// Returns [`None`] if the script is not contained in the [`TaprootSpendInfo`]
+    /// If there are multiple ControlBlocks possible, this returns the shortest one.
+    pub fn control_block(&self, script_ver: &(Script, LeafVersion)) -> Option<ControlBlock> {
+        let merkle_branch_set = self.script_map.get(script_ver)?;
+        // Choose the smallest one amongst the multiple script maps
+        let smallest = merkle_branch_set
+            .iter()
+            .min_by(|x, y| x.0.len().cmp(&y.0.len()))
+            .expect("Invariant: Script map key must contain non-empty set value");
+        Some(ControlBlock {
+            internal_key: self.internal_key,
+            output_key_parity: self.output_key_parity,
+            leaf_version: LeafVersion::default(),
+            merkle_branch: smallest.clone(),
+        })
+    }
+}
+
+/// Builder for building taproot iteratively. Users can specify tap leaf or omitted/hidden
+/// branches in a DFS(Depth first search) walk to construct this tree.
+// Similar to Taproot Builder in bitcoin core
+#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct TaprootBuilder {
+    // The following doc-comment is from bitcoin core, but modified for rust
+    // The comment below describes the current state of the builder for a given tree.
+    //
+    // For each level in the tree, one NodeInfo object may be present. branch at index 0
+    // is information about the root; further values are for deeper subtrees being
+    // explored.
+    //
+    // During the construction of Taptree, for every right branch taken to
+    // reach the position we're currently working in, there will be a (Some(_))
+    // entry in branch corresponding to the left branch at that level.
+    //
+    // For example, imagine this tree:     - N0 -
+    //                                    /      \
+    //                                   N1      N2
+    //                                  /  \    /  \
+    //                                 A    B  C   N3
+    //                                            /  \
+    //                                           D    E
+    //
+    // Initially, branch is empty. After processing leaf A, it would become
+    // {None, None, A}. When processing leaf B, an entry at level 2 already
+    // exists, and it would thus be combined with it to produce a level 1 one,
+    // resulting in {None, N1}. Adding C and D takes us to {None, N1, C}
+    // and {None, N1, C, D} respectively. When E is processed, it is combined
+    // with D, and then C, and then N1, to produce the root, resulting in {N0}.
+    //
+    // This structure allows processing with just O(log n) overhead if the leaves
+    // are computed on the fly.
+    //
+    // As an invariant, there can never be None entries at the end. There can
+    // also not be more than 128 entries (as that would mean more than 128 levels
+    // in the tree). The depth of newly added entries will always be at least
+    // equal to the current size of branch (otherwise it does not correspond
+    // to a depth-first traversal of a tree). branch is only empty if no entries
+    // have ever be processed. branch having length 1 corresponds to being done.
+    //
+    branch: Vec<Option<NodeInfo>>,
+}
+
+impl TaprootBuilder {
+    /// Create a new instance of [`TaprootBuilder`]
+    pub fn new() -> Self {
+        TaprootBuilder { branch: vec![] }
+    }
+    /// Just like [`TaprootBuilder::add_leaf`] but allows to specify script version
+    pub fn add_leaf_with_ver(
+        self,
+        depth: usize,
+        script: Script,
+        ver: LeafVersion,
+    ) -> Result<Self, TaprootBuilderError> {
+        let leaf = NodeInfo::new_leaf_with_ver(script, ver);
+        self.insert(leaf, depth)
+    }
+
+    /// Add a leaf script at a depth `depth` to the builder with default script version.
+    /// This will error if the leave are not provided in a DFS walk order. The depth of the
+    /// root node is 0 and it's immediate child would be at depth 1.
+    /// See [`TaprootBuilder::add_leaf_with_ver`] for adding a leaf with specific version
+    /// See [Wikipedia](https://en.wikipedia.org/wiki/Depth-first_search) for more details
+    pub fn add_leaf(self, depth: usize, script: Script) -> Result<Self, TaprootBuilderError> {
+        self.add_leaf_with_ver(depth, script, LeafVersion::default())
+    }
+
+    /// Add a hidden/omitted node at a depth `depth` to the builder.
+    /// This will error if the node are not provided in a DFS walk order. The depth of the
+    /// root node is 0 and it's immediate child would be at depth 1.
+    pub fn add_hidden(self, depth: usize, hash: sha256::Hash) -> Result<Self, TaprootBuilderError> {
+        let node = NodeInfo::new_hidden(hash);
+        self.insert(node, depth)
+    }
+
+    /// Create [`TaprootSpendInfo`] with the given internal key
+    pub fn finalize<C: secp256k1::Verification>(
+        mut self,
+        secp: &Secp256k1<C>,
+        internal_key: schnorr::PublicKey,
+    ) -> Result<TaprootSpendInfo, TaprootBuilderError> {
+        if self.branch.len() > 1 {
+            return Err(TaprootBuilderError::IncompleteTree);
+        }
+        let node = self
+            .branch
+            .pop()
+            .ok_or(TaprootBuilderError::EmptyTree)?
+            .expect("Builder invariant: last element of the branch must be some");
+        Ok(TaprootSpendInfo::from_node_info(secp, internal_key, node))
+    }
+
+    // Helper function to insert a leaf at a depth
+    fn insert(mut self, mut node: NodeInfo, mut depth: usize) -> Result<Self, TaprootBuilderError> {
+        // early error on invalid depth. Though this will be checked later
+        // while constructing TaprootMerkelBranch
+        if depth > TAPROOT_CONTROL_MAX_NODE_COUNT {
+            return Err(TaprootBuilderError::InvalidMerkleTreeDepth(depth));
+        }
+        // We cannot insert a leaf at a lower depth while a deeper branch is unfinished. Doing
+        // so would mean the add_leaf/add_hidden invocations do not correspond to a DFS traversal of a
+        // binary tree.
+        if depth + 1 < self.branch.len() {
+            return Err(TaprootBuilderError::NodeNotInDfsOrder);
+        }
+
+        while self.branch.len() == depth + 1 {
+            let child = match self.branch.pop() {
+                None => unreachable!("Len of branch checked to be >= 1"),
+                Some(Some(child)) => child,
+                // Needs an explicit push to add the None that we just popped.
+                // Cannot use .last() because of borrow checker issues.
+                Some(None) => {
+                    self.branch.push(None);
+                    break;
+                } // Cannot combine further
+            };
+            if depth == 0 {
+                // We are trying to combine two nodes at root level.
+                // Can't propagate further up than the root
+                return Err(TaprootBuilderError::OverCompleteTree);
+            }
+            node = NodeInfo::combine(node, child)?;
+            // Propagate to combine nodes at a lower depth
+            depth -= 1;
+        }
+
+        if self.branch.len() < depth + 1 {
+            // add enough nodes so that we can insert node at depth `depth`
+            let num_extra_nodes = depth + 1 - self.branch.len();
+            self.branch
+                .extend((0..num_extra_nodes).into_iter().map(|_| None));
+        }
+        // Push the last node to the branch
+        self.branch[depth] = Some(node);
+        Ok(self)
+    }
+}
+
+// Internally used structure to represent the node information in taproot tree
+#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+struct NodeInfo {
+    /// Merkle Hash for this node
+    hash: sha256::Hash,
+    /// information about leaves inside this node
+    leaves: Vec<LeafInfo>,
+}
+
+impl NodeInfo {
+    // Create a new NodeInfo with omitted/hidden info
+    fn new_hidden(hash: sha256::Hash) -> Self {
+        Self {
+            hash: hash,
+            leaves: vec![],
+        }
+    }
+
+    // Create a new leaf with NodeInfo
+    fn new_leaf_with_ver(script: Script, ver: LeafVersion) -> Self {
+        let leaf = LeafInfo::new(script, ver);
+        Self {
+            hash: leaf.hash(),
+            leaves: vec![leaf],
+        }
+    }
+
+    // Combine two NodeInfo's to create a new parent
+    fn combine(a: Self, b: Self) -> Result<Self, TaprootBuilderError> {
+        let mut all_leaves = Vec::with_capacity(a.leaves.len() + b.leaves.len());
+        for mut a_leaf in a.leaves {
+            a_leaf.merkle_branch.push(b.hash)?; // add hashing partner
+            all_leaves.push(a_leaf);
+        }
+        for mut b_leaf in b.leaves {
+            b_leaf.merkle_branch.push(a.hash)?; // add hashing partner
+            all_leaves.push(b_leaf);
+        }
+        let mut eng = TapBranchHash::engine();
+        if a.hash < b.hash {
+            eng.input(&a.hash);
+            eng.input(&b.hash);
+        } else {
+            eng.input(&b.hash);
+            eng.input(&a.hash);
+        };
+        Ok(Self {
+            hash: sha256::Hash::from_engine(eng),
+            leaves: all_leaves,
+        })
+    }
+}
+
+// Internally used structure to store information about taproot leaf node
+#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+struct LeafInfo {
+    // The underlying script
+    script: Script,
+    // The leaf version
+    ver: LeafVersion,
+    // The merkle proof(hashing partners) to get this node
+    merkle_branch: TaprootMerkleBranch,
+}
+
+impl LeafInfo {
+    // Create an instance of Self from Script with default version and no merkle branch
+    fn new(script: Script, ver: LeafVersion) -> Self {
+        Self {
+            script: script,
+            ver: ver,
+            merkle_branch: TaprootMerkleBranch(vec![]),
+        }
+    }
+
+    // Compute a leaf hash for the given leaf
+    fn hash(&self) -> sha256::Hash {
+        let leaf_hash = TapLeafHash::from_script(&self.script, self.ver);
+        sha256::Hash::from_inner(leaf_hash.into_inner())
+    }
+}
+
+/// The Merkle proof for inclusion of a tree in a taptree hash
+// The type of hash is sha256::Hash because the vector might contain
+// both TapBranchHash and TapLeafHash
+#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Default)]
+pub struct TaprootMerkleBranch(Vec<sha256::Hash>);
+
+impl TaprootMerkleBranch {
+    /// Obtain a reference to inner
+    pub fn as_inner(&self) -> &[sha256::Hash] {
+        &self.0
+    }
+
+    /// Create a merkle proof from slice
+    pub fn from_slice(sl: &[u8]) -> Result<Self, TaprootError> {
+        if sl.len() % TAPROOT_CONTROL_NODE_SIZE != 0 {
+            Err(TaprootError::InvalidMerkleBranchSize(sl.len()))
+        } else if sl.len() > TAPROOT_CONTROL_NODE_SIZE * TAPROOT_CONTROL_MAX_NODE_COUNT {
+            Err(TaprootError::InvalidMerkleTreeDepth(
+                sl.len() / TAPROOT_CONTROL_NODE_SIZE,
+            ))
+        } else {
+            let inner = sl
+                // TODO: Use chunks_exact after MSRV changes to 1.31
+                .chunks(TAPROOT_CONTROL_NODE_SIZE)
+                .map(|chunk| {
+                    sha256::Hash::from_slice(chunk)
+                        .expect("chunk exact always returns the correct size")
+                })
+                .collect();
+            Ok(TaprootMerkleBranch(inner))
+        }
+    }
+
+    /// Serialize to a writer. Returns the number of bytes written
+    pub fn encode<Write: io::Write>(&self, mut writer: Write) -> io::Result<usize> {
+        let mut written = 0;
+        for hash in self.0.iter() {
+            written += writer.write(hash)?;
+        }
+        Ok(written)
+    }
+
+    /// Serialize self as bytes
+    pub fn serialize(&self) -> Vec<u8> {
+        self.0.iter().map(|e| e.as_inner()).flatten().map(|x| *x).collect::<Vec<u8>>()
+    }
+
+    // Internal function to append elements to proof
+    fn push(&mut self, h: sha256::Hash) -> Result<(), TaprootBuilderError> {
+        if self.0.len() >= TAPROOT_CONTROL_MAX_NODE_COUNT {
+            Err(TaprootBuilderError::InvalidMerkleTreeDepth(self.0.len()))
+        } else {
+            self.0.push(h);
+            Ok(())
+        }
+    }
+
+    /// Create a MerkleProof from Vec<[`sha256::Hash`]>. Returns an error when
+    /// inner proof len is more than TAPROOT_CONTROL_MAX_NODE_COUNT (128)
+    pub fn from_inner(inner: Vec<sha256::Hash>) -> Result<Self, TaprootError> {
+        if inner.len() > TAPROOT_CONTROL_MAX_NODE_COUNT {
+            Err(TaprootError::InvalidMerkleTreeDepth(inner.len()))
+        } else {
+            Ok(TaprootMerkleBranch(inner))
+        }
+    }
+
+    /// Consume Self to get Vec<[`sha256::Hash`]>
+    pub fn into_inner(self) -> Vec<sha256::Hash> {
+        self.0
+    }
+}
+
+/// Control Block data structure used in Tapscript satisfaction
+#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct ControlBlock {
+    /// The tapleaf version,
+    pub leaf_version: LeafVersion,
+    /// The parity of the output key (NOT THE INTERNAL KEY WHICH IS ALWAYS XONLY)
+    pub output_key_parity: bool,
+    /// The internal key
+    pub internal_key: schnorr::PublicKey,
+    /// The merkle proof of a script associated with this leaf
+    pub merkle_branch: TaprootMerkleBranch,
+}
+
+impl ControlBlock {
+    /// Obtain a ControlBlock from slice. This is an extra witness element
+    /// that provides the proof that taproot script pubkey is correctly computed
+    /// with some specified leaf hash. This is the last element in
+    /// taproot witness when spending a output via script path.
+    ///
+    /// # Errors:
+    /// - If the control block size is not of the form 33 + 32m where
+    /// 0 <= m <= 128, InvalidControlBlock is returned
+    pub fn from_slice(sl: &[u8]) -> Result<ControlBlock, TaprootError> {
+        if sl.len() < TAPROOT_CONTROL_BASE_SIZE
+            || (sl.len() - TAPROOT_CONTROL_BASE_SIZE) % TAPROOT_CONTROL_NODE_SIZE != 0
+        {
+            return Err(TaprootError::InvalidControlBlockSize(sl.len()));
+        }
+        let output_key_parity = (sl[0] & 1) == 1;
+        let leaf_version = LeafVersion::from_u8(sl[0] & TAPROOT_LEAF_MASK)?;
+        let internal_key = schnorr::PublicKey::from_slice(&sl[1..TAPROOT_CONTROL_BASE_SIZE])
+            .map_err(TaprootError::InvalidInternalKey)?;
+        let merkle_branch = TaprootMerkleBranch::from_slice(&sl[TAPROOT_CONTROL_BASE_SIZE..])?;
+        Ok(ControlBlock {
+            leaf_version,
+            output_key_parity,
+            internal_key,
+            merkle_branch,
+        })
+    }
+
+    /// Obtain the size of control block. Faster and more efficient than calling
+    /// serialize() followed by len(). Can be handy for fee estimation
+    pub fn size(&self) -> usize {
+        TAPROOT_CONTROL_BASE_SIZE + TAPROOT_CONTROL_NODE_SIZE * self.merkle_branch.as_inner().len()
+    }
+
+    /// Serialize to a writer. Returns the number of bytes written
+    pub fn encode<Write: io::Write>(&self, mut writer: Write) -> io::Result<usize> {
+        let first_byte: u8 =
+            (if self.output_key_parity { 1 } else { 0 }) | self.leaf_version.as_u8();
+        let mut bytes_written = 0;
+        bytes_written += writer.write(&[first_byte])?;
+        bytes_written += writer.write(&self.internal_key.serialize())?;
+        bytes_written += self.merkle_branch.encode(&mut writer)?;
+        Ok(bytes_written)
+    }
+
+    /// Serialize the control block. This would be required when
+    /// using ControlBlock as a witness element while spending an output via
+    /// script path. This serialization does not include the VarInt prefix that would be
+    /// applied when encoding this element as a witness.
+    pub fn serialize(&self) -> Vec<u8> {
+        let mut buf = Vec::with_capacity(self.size());
+        self.encode(&mut buf)
+            .expect("writers don't error");
+        buf
+    }
+
+    /// Verify that a control block is correct proof for a given output key and script
+    /// This only checks that script is contained inside the taptree described by
+    /// output key, full verification must also execute the script with witness data
+    pub fn verify_taproot_commitment<C: secp256k1::Verification>(
+        &self,
+        secp: &Secp256k1<C>,
+        output_key: &schnorr::PublicKey,
+        script: &Script,
+    ) -> bool {
+        // compute the script hash
+        // Initially the curr_hash is the leaf hash
+        let leaf_hash = TapLeafHash::from_script(&script, self.leaf_version);
+        let mut curr_hash = TapBranchHash::from_inner(leaf_hash.into_inner());
+        // Verify the proof
+        for elem in self.merkle_branch.as_inner() {
+            let mut eng = TapBranchHash::engine();
+            if curr_hash.as_inner() < elem.as_inner() {
+                eng.input(&curr_hash);
+                eng.input(elem);
+            } else {
+                eng.input(elem);
+                eng.input(&curr_hash);
+            }
+            // Recalculate the curr hash as parent hash
+            curr_hash = TapBranchHash::from_engine(eng);
+        }
+        // compute the taptweak
+        let tweak = TapTweakHash::from_key_and_tweak(self.internal_key, Some(curr_hash));
+        self.internal_key.tweak_add_check(
+            secp,
+            output_key,
+            self.output_key_parity,
+            tweak.into_inner(),
+        )
+    }
+}
+
+/// The leaf version for tapleafs
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct LeafVersion(u8);
+
+impl Default for LeafVersion {
+    fn default() -> Self {
+        LeafVersion(TAPROOT_LEAF_TAPSCRIPT)
+    }
+}
+
+impl LeafVersion {
+    /// Obtain LeafVersion from u8, will error when last bit of ver is even or
+    /// when ver is 0x50 (ANNEX_TAG)
+    // Text from BIP341:
+    // In order to support some forms of static analysis that rely on
+    // being able to identify script spends without access to the output being
+    // spent, it is recommended to avoid using any leaf versions that would conflict
+    // with a valid first byte of either a valid P2WPKH pubkey or a valid P2WSH script
+    // (that is, both v and v | 1 should be an undefined, invalid or disabled opcode
+    // or an opcode that is not valid as the first opcode).
+    // The values that comply to this rule are the 32 even values between
+    // 0xc0 and 0xfe and also 0x66, 0x7e, 0x80, 0x84, 0x96, 0x98, 0xba, 0xbc, 0xbe
+    pub fn from_u8(ver: u8) -> Result<Self, TaprootError> {
+        if ver & TAPROOT_LEAF_MASK == ver && ver != 0x50 {
+            Ok(LeafVersion(ver))
+        } else {
+            Err(TaprootError::InvalidTaprootLeafVersion(ver))
+        }
+    }
+
+    /// Get the inner version from LeafVersion
+    pub fn as_u8(&self) -> u8 {
+        self.0
+    }
+}
+
+impl Into<u8> for LeafVersion {
+    fn into(self) -> u8 {
+        self.0
+    }
+}
+
+/// Detailed error type for taproot builder
+#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub enum TaprootBuilderError {
+    /// Merkle Tree depth must not be more than 128
+    InvalidMerkleTreeDepth(usize),
+    /// Nodes must be added specified in DFS order
+    NodeNotInDfsOrder,
+    /// Two nodes at depth 0 are not allowed
+    OverCompleteTree,
+    /// Invalid taproot internal key
+    InvalidInternalKey(secp256k1::Error),
+    /// Called finalize on an incomplete tree
+    IncompleteTree,
+    /// Called finalize on a empty tree
+    EmptyTree,
+    /// Script weight overflow
+    ScriptWeightOverflow,
+}
+
+impl fmt::Display for TaprootBuilderError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match *self {
+            TaprootBuilderError::NodeNotInDfsOrder => {
+                write!(f, "add_leaf/add_hidden must be called in DFS walk order",)
+            }
+            TaprootBuilderError::OverCompleteTree => write!(
+                f,
+                "Attempted to create a tree with two nodes at depth 0. There must\
+                only be a exactly one node at depth 0",
+            ),
+            TaprootBuilderError::InvalidMerkleTreeDepth(d) => write!(
+                f,
+                "Merkle Tree depth({}) must be less than {}",
+                d, TAPROOT_CONTROL_MAX_NODE_COUNT
+            ),
+            TaprootBuilderError::InvalidInternalKey(e) => {
+                write!(f, "Invalid Internal XOnly key : {}", e)
+            }
+            TaprootBuilderError::IncompleteTree => {
+                write!(f, "Called finalize on an incomplete tree")
+            }
+            TaprootBuilderError::EmptyTree => {
+                write!(f, "Called finalize on an empty tree")
+            }
+            TaprootBuilderError::ScriptWeightOverflow => {
+                write!(f, "Script weight overflow in Huffman tree construction")
+            },
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
+impl error::Error for TaprootBuilderError {}
+
+/// Detailed error type for taproot utilities
+#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub enum TaprootError {
+    /// Proof size must be a multiple of 32
+    InvalidMerkleBranchSize(usize),
+    /// Merkle Tree depth must not be more than 128
+    InvalidMerkleTreeDepth(usize),
+    /// The last bit of tapleaf version must be zero
+    InvalidTaprootLeafVersion(u8),
+    /// Invalid Control Block Size
+    InvalidControlBlockSize(usize),
+    /// Invalid taproot internal key
+    InvalidInternalKey(secp256k1::Error),
+    /// Empty TapTree
+    EmptyTree,
+}
+
+impl fmt::Display for TaprootError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match *self {
+            TaprootError::InvalidMerkleBranchSize(sz) => write!(
+                f,
+                "Merkle branch size({}) must be a multiple of {}",
+                sz, TAPROOT_CONTROL_NODE_SIZE
+            ),
+            TaprootError::InvalidMerkleTreeDepth(d) => write!(
+                f,
+                "Merkle Tree depth({}) must be less than {}",
+                d, TAPROOT_CONTROL_MAX_NODE_COUNT
+            ),
+            TaprootError::InvalidTaprootLeafVersion(v) => write!(
+                f,
+                "Leaf version({}) must have the least significant bit 0",
+                v
+            ),
+            TaprootError::InvalidControlBlockSize(sz) => write!(
+                f,
+                "Control Block size({}) must be of the form 33 + 32*m where  0 <= m <= {} ",
+                sz, TAPROOT_CONTROL_MAX_NODE_COUNT
+            ),
+            // TODO: add source when in MSRV
+            TaprootError::InvalidInternalKey(e) => write!(f, "Invalid Internal XOnly key : {}", e),
+            TaprootError::EmptyTree => write!(f, "Taproot Tree must contain at least one script"),
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
+impl error::Error for TaprootError {}
 #[cfg(test)]
 mod test {
     use super::*;
-    use hashes::hex::ToHex;
+    use hashes::hex::{FromHex, ToHex};
     use hashes::sha256t::Tag;
     use hashes::{sha256, Hash, HashEngine};
+    use secp256k1::VerifyOnly;
+    use core::str::FromStr;
 
     fn tag_engine(tag_name: &str) -> sha256::HashEngine {
         let mut engine = sha256::Hash::engine();
@@ -169,4 +980,105 @@ mod test {
             "cd10c023c300fb9a507dff136370fba1d8a0566667cfafc4099a8803e00dfdc2"
         );
     }
+
+    fn _verify_tap_commitments(secp: &Secp256k1<VerifyOnly>, out_spk_hex: &str, script_hex : &str, control_block_hex: &str) {
+        let out_pk = schnorr::PublicKey::from_str(&out_spk_hex[4..]).unwrap();
+        let script = Script::from_hex(script_hex).unwrap();
+        let control_block = ControlBlock::from_slice(&Vec::<u8>::from_hex(control_block_hex).unwrap()).unwrap();
+        assert_eq!(control_block_hex, control_block.serialize().to_hex());
+        assert!(control_block.verify_taproot_commitment(secp, &out_pk, &script));
+    }
+
+    #[test]
+    fn control_block_verify() {
+        let secp  = Secp256k1::verification_only();
+        // test vectors obtained from printing values in feature_taproot.py from bitcoin core
+        _verify_tap_commitments(&secp, "51205dc8e62b15e0ebdf44751676be35ba32eed2e84608b290d4061bbff136cd7ba9", "6a", "c1a9d6f66cd4b25004f526bfa873e56942f98e8e492bd79ed6532b966104817c2bda584e7d32612381cf88edc1c02e28a296e807c16ad22f591ee113946e48a71e0641e660d1e5392fb79d64838c2b84faf04b7f5f283c9d8bf83e39e177b64372a0cd22eeab7e093873e851e247714eff762d8a30be699ba4456cfe6491b282e193a071350ae099005a5950d74f73ba13077a57bc478007fb0e4d1099ce9cf3d4");
+        _verify_tap_commitments(&secp, "5120e208c869c40d8827101c5ad3238018de0f3f5183d77a0c53d18ac28ddcbcd8ad", "f4", "c0a0eb12e60a52614986c623cbb6621dcdba3a47e3be6b37e032b7a11c7b98f40090ab1f4890d51115998242ebce636efb9ede1b516d9eb8952dc1068e0335306199aaf103cceb41d9bc37ec231aca89b984b5fd3c65977ce764d51033ac65adb4da14e029b1e154a85bfd9139e7aa2720b6070a4ceba8264ca61d5d3ac27aceb9ef4b54cd43c2d1fd5e11b5c2e93cf29b91ea3dc5b832201f02f7473a28c63246");
+        _verify_tap_commitments(&secp, "5120567666e7df90e0450bb608e17c01ed3fbcfa5355a5f8273e34e583bfaa70ce09", "203455139bf238a3067bd72ed77e0ab8db590330f55ed58dba7366b53bf4734279ac", "c1a0eb12e60a52614986c623cbb6621dcdba3a47e3be6b37e032b7a11c7b98f400");
+        _verify_tap_commitments(&secp, "5120580a19e47269414a55eb86d5d0c6c9b371455d9fd2154412a57dec840df99fe1", "6a", "bca0eb12e60a52614986c623cbb6621dcdba3a47e3be6b37e032b7a11c7b98f40042ba1bd1c63c03ccff60d4c4d53a653f87909eb3358e7fa45c9d805231fb08c933e1f4e0f9d17f591df1419df7d5b7eb5f744f404c5ef9ecdb1b89b18cafa3a816d8b5dba3205f9a9c05f866d91f40d2793a7586d502cb42f46c7a11f66ad4aa");
+        _verify_tap_commitments(&secp, "5120228b94a4806254a38d6efa8a134c28ebc89546209559dfe40b2b0493bafacc5b", "6a50", "c0a0eb12e60a52614986c623cbb6621dcdba3a47e3be6b37e032b7a11c7b98f4009c9aed3dfd11ab0e78bf87ef3bf296269dc4b0f7712140386d6980992bab4b45");
+        _verify_tap_commitments(&secp, "5120567666e7df90e0450bb608e17c01ed3fbcfa5355a5f8273e34e583bfaa70ce09", "203455139bf238a3067bd72ed77e0ab8db590330f55ed58dba7366b53bf4734279ac", "c1a0eb12e60a52614986c623cbb6621dcdba3a47e3be6b37e032b7a11c7b98f400");
+        _verify_tap_commitments(&secp, "5120b0a79103c31fe51eea61d2873bad8a25a310da319d7e7a85f825fa7a00ea3f85", "203455139bf238a3067bd72ed77e0ab8db590330f55ed58dba7366b53bf4734279ad51", "c1a0eb12e60a52614986c623cbb6621dcdba3a47e3be6b37e032b7a11c7b98f400");
+        _verify_tap_commitments(&secp, "5120f2f62e854a0012aeba78cd4ba4a0832447a5262d4c6eb4f1c95c7914b536fc6c", "6a86", "c1a0eb12e60a52614986c623cbb6621dcdba3a47e3be6b37e032b7a11c7b98f4009ad3d30479f0689dbdf59a6b840d60ad485b2effbed1825a75ce19a44e460e09056f60ea686d79cfa4fb79f197b2e905ac857a983be4a5a41a4873e865aa950780c0237de279dc063e67deec46ef8e1bc351bf12c4d67a6d568001faf097e797e6ee620f53cfe0f8acaddf2063c39c3577853bb46d61ffcba5a024c3e1216837");
+        _verify_tap_commitments(&secp, "51202a4772070b49bae68b44315032cdbf9c40c7c2f896781b32b931b73dbfb26d7e", "6af8", "c0a0eb12e60a52614986c623cbb6621dcdba3a47e3be6b37e032b7a11c7b98f4006f183944a14618fc7fe9ceade0f58e43a19d3c3b179ea6c43c29616413b6971c99aaf103cceb41d9bc37ec231aca89b984b5fd3c65977ce764d51033ac65adb4c3462adec78cd04f3cc156bdadec50def99feae0dc6a23664e8a2b0d42d6ca9eb968dfdf46c23af642b2688351904e0a0630e71ffac5bcaba33b9b2c8a7495ec");
+        _verify_tap_commitments(&secp, "5120a32b0b8cfafe0f0f8d5870030ba4d19a8725ad345cb3c8420f86ac4e0dff6207", "4c", "e8a0eb12e60a52614986c623cbb6621dcdba3a47e3be6b37e032b7a11c7b98f400615da7ac8d078e5fc7f4690fc2127ba40f0f97cc070ade5b3a7919783d91ef3f13734aab908ae998e57848a01268fe8217d70bc3ee8ea8ceae158ae964a4b5f3af20b50d7019bf47fde210eee5c52f1cfe71cfca78f2d3e7c1fd828c80351525");
+        _verify_tap_commitments(&secp, "5120b0a79103c31fe51eea61d2873bad8a25a310da319d7e7a85f825fa7a00ea3f85", "203455139bf238a3067bd72ed77e0ab8db590330f55ed58dba7366b53bf4734279ad51", "c1a0eb12e60a52614986c623cbb6621dcdba3a47e3be6b37e032b7a11c7b98f400");
+        _verify_tap_commitments(&secp, "51208678459f1fa0f80e9b89b8ffdcaf46a022bdf60aa45f1fed9a96145edf4ec400", "6a50", "c0a0eb12e60a52614986c623cbb6621dcdba3a47e3be6b37e032b7a11c7b98f4001eff29e1a89e650076b8d3c56302881d09c9df215774ed99993aaed14acd6615");
+        _verify_tap_commitments(&secp, "5120017316303aed02bcdec424c851c9eacbe192b013139bd9634c4e19b3475b06e1", "61", "02a0eb12e60a52614986c623cbb6621dcdba3a47e3be6b37e032b7a11c7b98f40050462265ca552b23cbb4fe021b474313c8cb87d4a18b3f7bdbeb2b418279ba31fc6509d829cd42336f563363cb3538d78758e0876c71e13012eb2b656eb0edb051a2420a840d5c8c6c762abc7410af2c311f606b20ca2ace56a8139f84b1379a");
+        _verify_tap_commitments(&secp, "5120896d4d5d2236e86c6e9320e86d1a7822e652907cbd508360e8c71aefc127c77d", "61", "14a0eb12e60a52614986c623cbb6621dcdba3a47e3be6b37e032b7a11c7b98f4001ab0e9d9a4858a0e69605fe9c5a42d739fbe26fa79650e7074f462b02645f7ea1c91802b298cd91e6b5af57c6a013d93397cd2ecbd5569382cc27becf44ff4fff8960b20f846160c159c58350f6b6072cf1b3daa5185b7a42524fb72cbc252576ae46732b8e31ac24bfa7d72f4c3713e8696f99d8ac6c07e4c820a03f249f144");
+        _verify_tap_commitments(&secp, "512093c7378d96518a75448821c4f7c8f4bae7ce60f804d03d1f0628dd5dd0f5de51", "04ffffffff203455139bf238a3067bd72ed77e0ab8db590330f55ed58dba7366b53bf4734279ba04feffffff87ab", "c1a0eb12e60a52614986c623cbb6621dcdba3a47e3be6b37e032b7a11c7b98f400c9a5cd1f6c8a81f5648e39f9810591df1c9a8f1fe97c92e03ecd7c0c016c951983e05473c6e8238cb4c780ea2ce62552b2a3eee068ceffc00517cd7b97e10dad");
+        _verify_tap_commitments(&secp, "5120b28d75a7179de6feb66b8bb0bfa2b2c739d1a41cf7366a1b393804a844db8a28", "61", "c4a0eb12e60a52614986c623cbb6621dcdba3a47e3be6b37e032b7a11c7b98f400eebc95ded88fb8050094e8dfa958c3be0894eaff0fafae678206b26918d8d7ac47039d40fe34d04b4155df7f1be7f2a49253c7e87812ea9e569e683ac27459e652d6503aa32d64734d00adfee8798b2eed28858abf3bd038e8fa58eb7df4a2d9");
+        _verify_tap_commitments(&secp, "512043e4aa733fc6f43c78a31c2b3c192623acf5cc8c01199ebcc4de88067baca83e", "bd4c", "c1a0eb12e60a52614986c623cbb6621dcdba3a47e3be6b37e032b7a11c7b98f4003f7be6f8848b5bddf332c4d7bd83077f73701e2479f70e02b5730e841234d082b8b41ebea96ffd937715d9faeaa6895e6ef3b22919c554b75df12b3371d328023e443d1df50634ecc1cd169803a1e546f0d44304d8fc5056c408e597fed469b8437d6660eaad3cf72e35ba6e5ff7ddd5e293c1e7e813c871df4f46508e9946ec");
+        _verify_tap_commitments(&secp, "5120ee9aecb28f5f35ce1f8b5ec80275ac0f81bca4a21b29b4632fb4bcbef8823e6a", "2021a5981b13be29c9d4ea179ea44a8b773ea8c02d68f6f6eefd98de20d4bd055fac", "c13359c284c196b6e80f0cf1d93b6a397cf7ee722f0427b705bd954b88ada8838bd2622fd0e104fc50aa763b43c6a792d7d117029983abd687223b4344a9402c618bba7f5fc3fa8a57491f6842acde88c1e675ca35caea3b1a69ee2c2d9b10f615");
+        _verify_tap_commitments(&secp, "5120885274df2252b44764dcef53c21f21154e8488b7e79fafbc96b9ebb22ad0200d", "6a50", "c1a0eb12e60a52614986c623cbb6621dcdba3a47e3be6b37e032b7a11c7b98f4000793597254158918e3369507f2d6fdbef17d18b1028bbb0719450ded0f42c58f");
+        _verify_tap_commitments(&secp, "512066f6f6f91d47674d198a28388e1eb05ec24e6ddbba10f16396b1a80c08675121", "6a50", "c1a0eb12e60a52614986c623cbb6621dcdba3a47e3be6b37e032b7a11c7b98f400fe92aff70a2e8e2a4f34a913b99612468a41e0f8ecaff9a729a173d11013c27e");
+        _verify_tap_commitments(&secp, "5120868ed9307bd4637491ff03e3aa2c216a08fe213cac8b6cedbb9ab31dbfa6512c", "61", "a2a0eb12e60a52614986c623cbb6621dcdba3a47e3be6b37e032b7a11c7b98f400da584e7d32612381cf88edc1c02e28a296e807c16ad22f591ee113946e48a71e46c7eccffefd2d573ec014130e508f0c9963ccebd7830409f7b1b1301725e9fa759d4ef857ec8e0bb42d6d31609d3c7e77de3bfa28c38f93393a6ddbabe819ec560ed4f061fbe742a5fd2a648d5209469420434c8753da3fa7067cc2bb4c172a");
+        _verify_tap_commitments(&secp, "5120c1a00a9baa82888fd7d30291135a7eaa9e9966a5f16db2b10460572f8b108d8d", "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000", "5ba0eb12e60a52614986c623cbb6621dcdba3a47e3be6b37e032b7a11c7b98f4007960d7b37dd1361aee34510e77acb4d27ddca17648a17e28475032538c1eb500f5a747f2c0893f79fe153ae918ac3d696de9322aa679aae62051ff5ed83aa502b338bd907346abd4cd9cf06117cb35d55a5a8dd950843522f8de7b5c7fba1804c38b0778d3d76b383f6db6fdf9d6e770da8fffbfa5152c0b8b38129885bcdee6");
+        _verify_tap_commitments(&secp, "5120bb9abeff7286b76dfc61800c548fe2621ff47506e47201a85c543b4a9a96fead", "75203455139bf238a3067bd72ed77e0ab8db590330f55ed58dba7366b53bf47342796ead6ead6ead6ead6ead6ead6ead6ead6ead6ead6ead6ead6eadac", "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");
+        _verify_tap_commitments(&secp, "5120afddc189ea51094b4cbf463806792e9c8b35dfdc5e01228c78376380d0046b00", "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", "c0a0eb12e60a52614986c623cbb6621dcdba3a47e3be6b37e032b7a11c7b98f400ff698adfda0327f188e2ee35f7aecc0f90c9138a350d450648d968c2b5dd7ef94ddd3ec418dc0d03ee4956feb708d838ed2b20e5a193465a6a1467fd3054e1ea141ea4c4c503a6271e19a090e2a69a24282e3be04c4f98720f7a0eb274d9693d13a8e3c139aa625fa2aefd09854570527f9ac545bda1b689719f5cb715612c07");
+        _verify_tap_commitments(&secp, "5120afddc189ea51094b4cbf463806792e9c8b35dfdc5e01228c78376380d0046b00", "83", "c0a0eb12e60a52614986c623cbb6621dcdba3a47e3be6b37e032b7a11c7b98f4007388cda01113397d4cd00bcfbd08fd68c3cfe3a42cbfe3a7651c1d5e6dacf1ad99aaf103cceb41d9bc37ec231aca89b984b5fd3c65977ce764d51033ac65adb4b59764bec92507e4a4c3f01a06f05980163ca10f1c549bfe01f85fa4f109a1295e607f5ed9f1008048474de336f11f67a1fbf2012f58944dede0ab19a3ca81f5");
+        _verify_tap_commitments(&secp, "512093c7378d96518a75448821c4f7c8f4bae7ce60f804d03d1f0628dd5dd0f5de51", "04ffffffff203455139bf238a3067bd72ed77e0ab8db590330f55ed58dba7366b53bf4734279ba04feffffff87ab", "c1a0eb12e60a52614986c623cbb6621dcdba3a47e3be6b37e032b7a11c7b98f400c9a5cd1f6c8a81f5648e39f9810591df1c9a8f1fe97c92e03ecd7c0c016c951983e05473c6e8238cb4c780ea2ce62552b2a3eee068ceffc00517cd7b97e10dad");
+    }
+
+    #[test]
+    fn build_huffman_tree() {
+        let secp = Secp256k1::verification_only();
+        let internal_key = schnorr::PublicKey::from_str("93c7378d96518a75448821c4f7c8f4bae7ce60f804d03d1f0628dd5dd0f5de51").unwrap();
+
+        let script_weights = vec![
+            (10, Script::from_hex("51").unwrap()), // semantics of script don't matter for this test
+            (20, Script::from_hex("52").unwrap()),
+            (20, Script::from_hex("53").unwrap()),
+            (30, Script::from_hex("54").unwrap()),
+            (20, Script::from_hex("55").unwrap()),
+        ];
+        let tree_info = TaprootSpendInfo::with_huffman_tree(&secp, internal_key, script_weights.clone()).unwrap();
+
+        // Obtain the output key
+        let output_key = tree_info.output_key();
+
+        // Try to create and verify a control block from each path
+        for (_weights, script) in script_weights {
+            let ver_script = (script, LeafVersion::default());
+            let ctrl_block = tree_info.control_block(&ver_script).unwrap();
+            assert!(ctrl_block.verify_taproot_commitment(&secp, &output_key, &ver_script.0))
+        }
+    }
+
+    #[test]
+    fn taptree_builder() {
+        let secp = Secp256k1::verification_only();
+        let internal_key = schnorr::PublicKey::from_str("93c7378d96518a75448821c4f7c8f4bae7ce60f804d03d1f0628dd5dd0f5de51").unwrap();
+
+        let builder = TaprootBuilder::new();
+        // Create a tree as shown below
+        // For example, imagine this tree:
+        // A, B , C are at depth 2 and D,E are at 3
+        //                                       ....
+        //                                     /      \
+        //                                    /\      /\
+        //                                   /  \    /  \
+        //                                  A    B  C  / \
+        //                                            D   E
+        let a = Script::from_hex("51").unwrap();
+        let b = Script::from_hex("52").unwrap();
+        let c = Script::from_hex("53").unwrap();
+        let d = Script::from_hex("54").unwrap();
+        let e = Script::from_hex("55").unwrap();
+        let builder = builder.add_leaf(2, a.clone()).unwrap();
+        let builder = builder.add_leaf(2, b.clone()).unwrap();
+        let builder = builder.add_leaf(2, c.clone()).unwrap();
+        let builder = builder.add_leaf(3, d.clone()).unwrap();
+        let builder = builder.add_leaf(3, e.clone()).unwrap();
+
+        let tree_info = builder.finalize(&secp, internal_key).unwrap();
+        let output_key = tree_info.output_key();
+
+        for script in vec![a, b, c, d, e] {
+            let ver_script = (script, LeafVersion::default());
+            let ctrl_block = tree_info.control_block(&ver_script).unwrap();
+            assert!(ctrl_block.verify_taproot_commitment(&secp, &output_key, &ver_script.0))
+        }
+    }
 }