diff --git a/lib/crypto/aes.js b/lib/crypto/aes.js
index dd579bc3..1bec1729 100644
--- a/lib/crypto/aes.js
+++ b/lib/crypto/aes.js
@@ -11,7 +11,6 @@
  */
 
 const crypto = require('crypto');
-const util = require('../utils/util');
 const native = require('../native').binding;
 
 /**
@@ -24,7 +23,7 @@ const native = require('../native').binding;
 
 exports.encipher = function encipher(data, key, iv) {
   let cipher = crypto.createCipheriv('aes-256-cbc', key, iv);
-  return util.concat(cipher.update(data), cipher.final());
+  return Buffer.concat([cipher.update(data), cipher.final()]);
 };
 
 /**
@@ -38,7 +37,7 @@ exports.encipher = function encipher(data, key, iv) {
 exports.decipher = function _decipher(data, key, iv) {
   let decipher = crypto.createDecipheriv('aes-256-cbc', key, iv);
   try {
-    return util.concat(decipher.update(data), decipher.final());
+    return Buffer.concat([decipher.update(data), decipher.final()]);
   } catch (e) {
     throw new Error('Bad key for decryption.');
   }
diff --git a/lib/crypto/digest-browser.js b/lib/crypto/digest-browser.js
index e27bc2cb..95a94e45 100644
--- a/lib/crypto/digest-browser.js
+++ b/lib/crypto/digest-browser.js
@@ -14,6 +14,7 @@
 const assert = require('assert');
 const hashjs = require('hash.js');
 const sha256 = require('./sha256');
+const POOL64 = Buffer.allocUnsafe(64);
 
 /**
  * Hash with chosen algorithm.
@@ -85,6 +86,25 @@ exports.hash256 = function hash256(data) {
   return sha256.hash256(data);
 };
 
+/**
+ * Hash left and right hashes with hash256.
+ * @param {Buffer} left
+ * @param {Buffer} right
+ * @returns {Buffer}
+ */
+
+exports.root256 = function root256(left, right) {
+  let data = POOL64;
+
+  assert(left.length === 32);
+  assert(right.length === 32);
+
+  left.copy(data, 0);
+  right.copy(data, 32);
+
+  return exports.hash256(data);
+};
+
 /**
  * Create an HMAC.
  * @param {String} alg
diff --git a/lib/crypto/digest.js b/lib/crypto/digest.js
index ef0d8dd2..9a23cb6f 100644
--- a/lib/crypto/digest.js
+++ b/lib/crypto/digest.js
@@ -10,8 +10,10 @@
  * @module crypto.digest
  */
 
+const assert = require('assert');
 const crypto = require('crypto');
 const native = require('../native').binding;
+const POOL64 = Buffer.allocUnsafe(64);
 
 /**
  * Hash with chosen algorithm.
@@ -74,6 +76,25 @@ exports.hash256 = function hash256(data) {
   return exports.sha256(exports.sha256(data));
 };
 
+/**
+ * Hash left and right hashes with hash256.
+ * @param {Buffer} left
+ * @param {Buffer} right
+ * @returns {Buffer}
+ */
+
+exports.root256 = function root256(left, right) {
+  let data = POOL64;
+
+  assert(left.length === 32);
+  assert(right.length === 32);
+
+  left.copy(data, 0);
+  right.copy(data, 32);
+
+  return exports.hash256(data);
+};
+
 /**
  * Create an HMAC.
  * @param {String} alg
@@ -95,4 +116,5 @@ if (native) {
   exports.sha256 = native.sha256;
   exports.hash160 = native.hash160;
   exports.hash256 = native.hash256;
+  exports.root256 = native.root256;
 }
diff --git a/lib/crypto/merkle.js b/lib/crypto/merkle.js
index b25b6674..89e0fe2b 100644
--- a/lib/crypto/merkle.js
+++ b/lib/crypto/merkle.js
@@ -25,7 +25,6 @@ exports.createTree = function createTree(leaves) {
   let nodes = leaves;
   let size = leaves.length;
   let malleated = false;
-  let data;
 
   if (size === 0) {
     let hash = Buffer.allocUnsafe(32);
@@ -34,8 +33,6 @@ exports.createTree = function createTree(leaves) {
     return [nodes, malleated];
   }
 
-  data = Buffer.allocUnsafe(64);
-
   for (let j = 0; size > 1; size = (size + 1) >>> 1) {
     for (let i = 0; i < size; i += 2) {
       let k = Math.min(i + 1, size - 1);
@@ -48,10 +45,7 @@ exports.createTree = function createTree(leaves) {
         malleated = true;
       }
 
-      left.copy(data, 0);
-      right.copy(data, 32);
-
-      hash = digest.hash256(data);
+      hash = digest.root256(left, right);
 
       nodes.push(hash);
     }
@@ -108,25 +102,17 @@ exports.createBranch = function createBranch(index, leaves) {
  */
 
 exports.verifyBranch = function verifyBranch(hash, branch, index) {
-  let data;
-
   if (branch.length === 0)
     return hash;
 
-  data = Buffer.allocUnsafe(64);
-
   for (let i = 0; i < branch.length; i++) {
     let otherside = branch[i];
 
-    if (index & 1) {
-      otherside.copy(data, 0);
-      hash.copy(data, 32);
-    } else {
-      hash.copy(data, 0);
-      otherside.copy(data, 32);
-    }
+    if (index & 1)
+      hash = digest.root256(otherside, hash);
+    else
+      hash = digest.root256(hash, otherside);
 
-    hash = digest.hash256(data);
     index >>>= 1;
   }
 
diff --git a/lib/mining/miner.js b/lib/mining/miner.js
index 88aae366..fc40bd3c 100644
--- a/lib/mining/miner.js
+++ b/lib/mining/miner.js
@@ -276,18 +276,18 @@ Miner.prototype.assemble = function assemble(attempt) {
     if (tx.isCoinbase())
       throw new Error('Cannot add coinbase to block.');
 
-    for (let input of tx.inputs) {
-      let prev = input.prevout.hash;
+    for (let {prevout} of tx.inputs) {
+      let hash = prevout.hash;
 
-      if (!this.mempool.hasEntry(prev))
+      if (!this.mempool.hasEntry(hash))
         continue;
 
       item.depCount += 1;
 
-      if (!depMap[prev])
-        depMap[prev] = [];
+      if (!depMap[hash])
+        depMap[hash] = [];
 
-      depMap[prev].push(item);
+      depMap[hash].push(item);
     }
 
     if (item.depCount > 0)
@@ -344,7 +344,7 @@ Miner.prototype.assemble = function assemble(attempt) {
     if (!deps)
       continue;
 
-    for (item of deps) {
+    for (let item of deps) {
       if (--item.depCount === 0)
         queue.insert(item);
     }
diff --git a/lib/mining/template.js b/lib/mining/template.js
index e106c997..6dd5e7a1 100644
--- a/lib/mining/template.js
+++ b/lib/mining/template.js
@@ -173,7 +173,7 @@ BlockTemplate.fromOptions = function fromOptions(options) {
 BlockTemplate.prototype.getWitnessHash = function getWitnessHash() {
   let nonce = encoding.ZERO_HASH;
   let leaves = [];
-  let root, malleated, data;
+  let root, malleated;
 
   leaves.push(encoding.ZERO_HASH);
 
@@ -184,9 +184,7 @@ BlockTemplate.prototype.getWitnessHash = function getWitnessHash() {
 
   assert(!malleated);
 
-  data = util.concat(root, nonce);
-
-  return digest.hash256(data);
+  return digest.root256(root, nonce);
 };
 
 /**
@@ -697,10 +695,8 @@ function MerkleTree() {
 }
 
 MerkleTree.prototype.withFirst = function withFirst(hash) {
-  for (let step of this.steps) {
-    let data = util.concat(hash, step);
-    hash = digest.hash256(data);
-  }
+  for (let step of this.steps)
+    hash = digest.root256(hash, step);
   return hash;
 };
 
@@ -757,8 +753,7 @@ MerkleTree.prototype.fromLeaves = function fromLeaves(leaves) {
       leaves.push(leaves[len - 1]);
 
     for (let i = 2; i < len; i += 2) {
-      let data = util.concat(leaves[i], leaves[i + 1]);
-      let hash = digest.hash256(data);
+      let hash = digest.root256(leaves[i], leaves[i + 1]);
       hashes.push(hash);
     }
 
diff --git a/lib/net/bip152.js b/lib/net/bip152.js
index ccf1e369..949ef7a5 100644
--- a/lib/net/bip152.js
+++ b/lib/net/bip152.js
@@ -400,7 +400,7 @@ CompactBlock.prototype.hasIndex = function hasIndex(index) {
  */
 
 CompactBlock.prototype.initKey = function initKey() {
-  let data = util.concat(this.abbr(), this.keyNonce);
+  let data = Buffer.concat([this.abbr(), this.keyNonce]);
   let hash = digest.sha256(data);
   this.sipKey = hash.slice(0, 16);
 };
diff --git a/lib/net/hostlist.js b/lib/net/hostlist.js
index 71293708..075c23a5 100644
--- a/lib/net/hostlist.js
+++ b/lib/net/hostlist.js
@@ -20,6 +20,7 @@ const seeds = require('./seeds');
 const dns = require('./dns');
 const Logger = require('../node/logger');
 const fs = require('../utils/fs');
+const POOL32 = Buffer.allocUnsafe(32);
 
 /**
  * Host List
@@ -459,7 +460,7 @@ HostList.prototype.getHost = function getHost() {
 HostList.prototype.freshBucket = function freshBucket(entry) {
   let addr = entry.addr;
   let src = entry.src;
-  let data = util.concat(addr.raw, src.raw);
+  let data = concat32(addr.raw, src.raw);
   let hash = murmur3(data, 0xfba4c795);
   let index = hash % this.fresh.length;
   return this.fresh[index];
@@ -1588,6 +1589,17 @@ HostListOptions.prototype.fromOptions = function fromOptions(options) {
   return this;
 };
 
+/*
+ * Helpers
+ */
+
+function concat32(left, right) {
+  let data = POOL32;
+  left.copy(data, 0);
+  right.copy(data, 32);
+  return data;
+}
+
 /*
  * Expose
  */
diff --git a/lib/primitives/block.js b/lib/primitives/block.js
index f80e4dbb..955aa22f 100644
--- a/lib/primitives/block.js
+++ b/lib/primitives/block.js
@@ -298,7 +298,7 @@ Block.prototype.createMerkleRoot = function createMerkleRoot(enc) {
  */
 
 Block.prototype.createWitnessNonce = function createWitnessNonce() {
-  return util.copy(encoding.ZERO_HASH);
+  return Buffer.from(encoding.ZERO_HASH);
 };
 
 /**
@@ -311,7 +311,7 @@ Block.prototype.createWitnessNonce = function createWitnessNonce() {
 Block.prototype.createCommitmentHash = function createCommitmentHash(enc) {
   let nonce = this.getWitnessNonce();
   let leaves = [];
-  let root, data, hash;
+  let root, hash;
 
   assert(nonce, 'No witness nonce present.');
 
@@ -327,9 +327,7 @@ Block.prototype.createCommitmentHash = function createCommitmentHash(enc) {
   // Note: malleation check ignored here.
   // assert(!malleated);
 
-  data = util.concat(root, nonce);
-
-  hash = digest.hash256(data);
+  hash = digest.root256(root, nonce);
 
   return enc === 'hex'
     ? hash.toString('hex')
diff --git a/lib/primitives/merkleblock.js b/lib/primitives/merkleblock.js
index 8bf09227..5ac28db6 100644
--- a/lib/primitives/merkleblock.js
+++ b/lib/primitives/merkleblock.js
@@ -17,7 +17,6 @@ const consensus = require('../protocol/consensus');
 const AbstractBlock = require('./abstractblock');
 const Headers = require('./headers');
 const DUMMY = Buffer.from([0]);
-const POOL = Buffer.allocUnsafe(64);
 
 /**
  * Represents a merkle (filtered) block.
@@ -200,7 +199,6 @@ MerkleBlock.prototype.extractTree = function extractTree() {
   let flags = this.flags;
   let totalTX = this.totalTX;
   let height = 0;
-  let data = POOL;
   let root;
 
   let width = (height) => {
@@ -246,10 +244,7 @@ MerkleBlock.prototype.extractTree = function extractTree() {
       right = left;
     }
 
-    left.copy(data, 0);
-    right.copy(data, 32);
-
-    return digest.hash256(data);
+    return digest.root256(left, right);
   };
 
   if (totalTX === 0)
@@ -566,7 +561,6 @@ MerkleBlock.fromMatches = function fromMatches(block, matches) {
   let hashes = [];
   let totalTX = block.txs.length;
   let height = 0;
-  let data = POOL;
   let flags, merkle;
 
   let width = (height) => {
@@ -586,10 +580,7 @@ MerkleBlock.fromMatches = function fromMatches(block, matches) {
     else
       right = left;
 
-    left.copy(data, 0);
-    right.copy(data, 32);
-
-    return digest.hash256(data);
+    return digest.root256(left, right);
   };
 
   let traverse = (height, pos, leaves, matches) => {
diff --git a/lib/primitives/tx.js b/lib/primitives/tx.js
index 71a76661..8924ba25 100644
--- a/lib/primitives/tx.js
+++ b/lib/primitives/tx.js
@@ -451,7 +451,7 @@ TX.prototype.signatureHashV0 = function signatureHashV0(index, prev, type) {
     // Bitcoind used to return 1 as an error code:
     // it ended up being treated like a hash.
     if (index >= this.outputs.length)
-      return util.copy(encoding.ONE_HASH);
+      return Buffer.from(encoding.ONE_HASH);
   }
 
   // Remove all code separators.
diff --git a/lib/script/sigcache.js b/lib/script/sigcache.js
index 61490c7a..c9940f82 100644
--- a/lib/script/sigcache.js
+++ b/lib/script/sigcache.js
@@ -131,8 +131,8 @@ SigCache.prototype.verify = function verify(msg, sig, key) {
  */
 
 function SigCacheEntry(sig, key) {
-  this.sig = util.copy(sig);
-  this.key = util.copy(key);
+  this.sig = Buffer.from(sig);
+  this.key = Buffer.from(key);
 }
 
 /**
diff --git a/lib/utils/util.js b/lib/utils/util.js
index 881e694b..447c2194 100644
--- a/lib/utils/util.js
+++ b/lib/utils/util.js
@@ -16,32 +16,6 @@ const nodeUtil = require('util');
 
 const util = exports;
 
-/**
- * Clone a buffer.
- * @param {Buffer} data
- * @returns {Buffer}
- */
-
-util.copy = function copy(data) {
-  let clone = Buffer.allocUnsafe(data.length);
-  data.copy(clone, 0, 0, data.length);
-  return clone;
-};
-
-/**
- * Concatenate two buffers.
- * @param {Buffer} a
- * @param {Buffer} b
- * @returns {Buffer}
- */
-
-util.concat = function concat(a, b) {
-  let data = Buffer.allocUnsafe(a.length + b.length);
-  a.copy(data, 0);
-  b.copy(data, a.length);
-  return data;
-};
-
 /**
  * Return hrtime (shim for browser).
  * @param {Array} time
@@ -108,6 +82,8 @@ util.revHex = function revHex(data) {
   let out = '';
 
   assert(typeof data === 'string');
+  assert(data.length > 0);
+  assert(data.length % 2 === 0);
 
   for (let i = 0; i < data.length; i += 2)
     out = data.slice(i, i + 2) + out;
@@ -769,15 +745,6 @@ util.binaryRemove = function binaryRemove(items, item, compare) {
   return true;
 };
 
-/**
- * Ensure hidden-class mode for object.
- * @param {Object} obj
- */
-
-util.fastProp = function fastProp(obj) {
-  ({ __proto__: obj });
-};
-
 /**
  * Quick test to see if a string is uppercase.
  * @param {String} str
diff --git a/package.json b/package.json
index 69f96c91..d5305901 100644
--- a/package.json
+++ b/package.json
@@ -28,7 +28,7 @@
     "n64": "0.0.11"
   },
   "optionalDependencies": {
-    "bcoin-native": "0.0.20",
+    "bcoin-native": "0.0.21",
     "leveldown": "1.7.0-0",
     "secp256k1": "3.2.5",
     "socket.io": "2.0.1",
diff --git a/test/chain-test.js b/test/chain-test.js
index dac47e64..94808c98 100644
--- a/test/chain-test.js
+++ b/test/chain-test.js
@@ -12,7 +12,6 @@ const MTX = require('../lib/primitives/mtx');
 const MemWallet = require('./util/memwallet');
 const Network = require('../lib/protocol/network');
 const Output = require('../lib/primitives/output');
-const util = require('../lib/utils/util');
 const common = require('../lib/blockchain/common');
 const opcodes = Script.opcodes;
 
@@ -547,7 +546,7 @@ describe('Chain', function() {
 
     assert(output.script.isCommitment());
 
-    commit = util.copy(output.script.get(1));
+    commit = Buffer.from(output.script.get(1));
     commit.fill(0, 10);
     output.script.set(1, commit);
     output.script.compile();