diff --git a/lib/crypto/pbkdf2.js b/lib/crypto/pbkdf2.js
index 3f387907..5e25a11f 100644
--- a/lib/crypto/pbkdf2.js
+++ b/lib/crypto/pbkdf2.js
@@ -11,7 +11,6 @@
  */
 
 const crypto = require('crypto');
-const co = require('../utils/co');
 
 /**
  * Perform key derivation using PBKDF2.
@@ -39,6 +38,12 @@ exports.derive = function derive(key, salt, iter, len, alg) {
 
 exports.deriveAsync = function deriveAsync(key, salt, iter, len, alg) {
   return new Promise((resolve, reject) => {
-    crypto.pbkdf2(key, salt, iter, len, alg, co.wrap(resolve, reject));
+    crypto.pbkdf2(key, salt, iter, len, alg, (err, result) => {
+      if (err) {
+        reject(err);
+        return;
+      }
+      resolve(result);
+    });
   });
 };
diff --git a/lib/crypto/scrypt.js b/lib/crypto/scrypt.js
index b07dedc6..b9fbe89e 100644
--- a/lib/crypto/scrypt.js
+++ b/lib/crypto/scrypt.js
@@ -39,7 +39,6 @@
  * @module crypto/scrypt
  */
 
-const co = require('../utils/co');
 const pbkdf2 = require('./pbkdf2');
 const native = require('../native').binding;
 
@@ -236,14 +235,14 @@ async function smixAsync(B, Bo, r, N, V, XY) {
   for (let i = 0; i < N; i++) {
     blkcpy(V, X, i * (128 * r), 0, 128 * r);
     blockmix_salsa8(X, Y, 128 * r, r);
-    await co.wait();
+    await wait();
   }
 
   for (let i = 0; i < N; i++) {
     const j = integerify(X, r) & (N - 1);
     blkxor(X, V, 0, j * (128 * r), 128 * r);
     blockmix_salsa8(X, Y, 128 * r, r);
-    await co.wait();
+    await wait();
   }
 
   blkcpy(B, X, Bo, 0, 128 * r);
@@ -258,6 +257,10 @@ function blkxor(dest, src, s1, s2, len) {
     dest[s1 + i] ^= src[s2 + i];
 }
 
+function wait() {
+  return new Promise(r => setImmediate(r));
+}
+
 /*
  * Expose
  */
diff --git a/lib/hd/private.js b/lib/hd/private.js
index a0e02df0..662bd01d 100644
--- a/lib/hd/private.js
+++ b/lib/hd/private.js
@@ -571,7 +571,7 @@ HDPrivateKey.prototype.fromReader = function fromReader(br, network) {
   this.privateKey = br.readBytes(32);
   this.publicKey = secp256k1.publicKeyCreate(this.privateKey, true);
 
-  br.verifyChecksum();
+  br.verifyChecksum(digest.hash256);
 
   return this;
 };
@@ -622,7 +622,7 @@ HDPrivateKey.prototype.toWriter = function toWriter(bw, network) {
   bw.writeBytes(this.chainCode);
   bw.writeU8(0);
   bw.writeBytes(this.privateKey);
-  bw.writeChecksum();
+  bw.writeChecksum(digest.hash256);
 
   return bw;
 };
diff --git a/lib/hd/public.js b/lib/hd/public.js
index a1ecc859..e2104294 100644
--- a/lib/hd/public.js
+++ b/lib/hd/public.js
@@ -440,7 +440,7 @@ HDPublicKey.prototype.fromReader = function fromReader(br, network) {
   this.chainCode = br.readBytes(32);
   this.publicKey = br.readBytes(33);
 
-  br.verifyChecksum();
+  br.verifyChecksum(digest.hash256);
 
   return this;
 };
@@ -481,7 +481,7 @@ HDPublicKey.prototype.toWriter = function toWriter(bw, network) {
   bw.writeU32BE(this.childIndex);
   bw.writeBytes(this.chainCode);
   bw.writeBytes(this.publicKey);
-  bw.writeChecksum();
+  bw.writeChecksum(digest.hash256);
 
   return bw;
 };
diff --git a/lib/net/bip150.js b/lib/net/bip150.js
index 810857bc..62d807ef 100644
--- a/lib/net/bip150.js
+++ b/lib/net/bip150.js
@@ -446,7 +446,7 @@ BIP150.address = function address(key) {
   bw.writeU8(0x0f);
   bw.writeU16BE(0xff01);
   bw.writeBytes(digest.hash160(key));
-  bw.writeChecksum();
+  bw.writeChecksum(digest.hash256);
   return base58.encode(bw.render());
 };
 
diff --git a/lib/primitives/address.js b/lib/primitives/address.js
index 2f105823..16068a66 100644
--- a/lib/primitives/address.js
+++ b/lib/primitives/address.js
@@ -200,7 +200,7 @@ Address.prototype.toRaw = function toRaw(network) {
   }
 
   bw.writeBytes(this.hash);
-  bw.writeChecksum();
+  bw.writeChecksum(digest.hash256);
 
   return bw.render();
 };
@@ -330,7 +330,7 @@ Address.prototype.fromRaw = function fromRaw(data, network) {
 
   const hash = br.readBytes(br.left() - 4);
 
-  br.verifyChecksum();
+  br.verifyChecksum(digest.hash256);
 
   return this.fromHash(hash, type, version);
 };
diff --git a/lib/primitives/keyring.js b/lib/primitives/keyring.js
index 529ce8ca..e74897ca 100644
--- a/lib/primitives/keyring.js
+++ b/lib/primitives/keyring.js
@@ -281,7 +281,7 @@ KeyRing.prototype.toSecret = function toSecret(network) {
   if (this.publicKey.length === 33)
     bw.writeU8(1);
 
-  bw.writeChecksum();
+  bw.writeChecksum(digest.hash256);
 
   return base58.encode(bw.render());
 };
@@ -309,7 +309,7 @@ KeyRing.prototype.fromSecret = function fromSecret(data, network) {
     compress = true;
   }
 
-  br.verifyChecksum();
+  br.verifyChecksum(digest.hash256);
 
   return this.fromPrivate(key, compress);
 };
diff --git a/lib/utils/reader.js b/lib/utils/reader.js
index c2e75c7a..f8d13b3c 100644
--- a/lib/utils/reader.js
+++ b/lib/utils/reader.js
@@ -9,7 +9,6 @@
 
 const assert = require('assert');
 const encoding = require('./encoding');
-const digest = require('../crypto/digest');
 
 const EMPTY = Buffer.alloc(0);
 
@@ -567,10 +566,11 @@ BufferReader.prototype.readNullString = function readNullString(enc) {
 
 /**
  * Create a checksum from the last start position.
+ * @param {Function} hash
  * @returns {Number} Checksum.
  */
 
-BufferReader.prototype.createChecksum = function createChecksum() {
+BufferReader.prototype.createChecksum = function createChecksum(hash) {
   let start = 0;
 
   if (this.stack.length > 0)
@@ -578,17 +578,18 @@ BufferReader.prototype.createChecksum = function createChecksum() {
 
   const data = this.data.slice(start, this.offset);
 
-  return digest.hash256(data).readUInt32LE(0, true);
+  return hash(data).readUInt32LE(0, true);
 };
 
 /**
  * Verify a 4-byte checksum against a calculated checksum.
+ * @param {Function} hash
  * @returns {Number} checksum
  * @throws on bad checksum
  */
 
-BufferReader.prototype.verifyChecksum = function verifyChecksum() {
-  const chk = this.createChecksum();
+BufferReader.prototype.verifyChecksum = function verifyChecksum(hash) {
+  const chk = this.createChecksum(hash);
   const checksum = this.readU32();
   this.enforce(chk === checksum, 'Checksum mismatch.');
   return checksum;
diff --git a/lib/utils/staticwriter.js b/lib/utils/staticwriter.js
index 0530c096..7e54ab4e 100644
--- a/lib/utils/staticwriter.js
+++ b/lib/utils/staticwriter.js
@@ -8,7 +8,6 @@
 
 const assert = require('assert');
 const encoding = require('./encoding');
-const digest = require('../crypto/digest');
 
 const EMPTY = Buffer.alloc(0);
 const POOLSIZE = 100 << 10;
@@ -429,12 +428,12 @@ StaticWriter.prototype.writeNullString = function writeNullString(value, enc) {
 
 /**
  * Calculate and write a checksum for the data written so far.
+ * @param {Function} hash
  */
 
-StaticWriter.prototype.writeChecksum = function writeChecksum() {
+StaticWriter.prototype.writeChecksum = function writeChecksum(hash) {
   const data = this.data.slice(0, this.offset);
-  const hash = digest.hash256(data);
-  hash.copy(this.data, this.offset, 0, 4);
+  hash(data).copy(this.data, this.offset, 0, 4);
   this.offset += 4;
 };
 
diff --git a/lib/utils/writer.js b/lib/utils/writer.js
index 700cfdbd..e641c31a 100644
--- a/lib/utils/writer.js
+++ b/lib/utils/writer.js
@@ -9,7 +9,6 @@
 
 const assert = require('assert');
 const encoding = require('./encoding');
-const digest = require('../crypto/digest');
 
 /*
  * Constants
@@ -168,7 +167,7 @@ BufferWriter.prototype.render = function render() {
         off += data.write(op.value, off, op.enc);
         break;
       case CHECKSUM:
-        off += digest.hash256(data.slice(0, off)).copy(data, off, 0, 4);
+        off += op.value(data.slice(0, off)).copy(data, off, 0, 4);
         break;
       case FILL:
         data.fill(op.value, off, off + op.size);
@@ -581,11 +580,12 @@ BufferWriter.prototype.writeNullString = function writeNullString(value, enc) {
 
 /**
  * Calculate and write a checksum for the data written so far.
+ * @param {Function} hash
  */
 
-BufferWriter.prototype.writeChecksum = function writeChecksum() {
+BufferWriter.prototype.writeChecksum = function writeChecksum(hash) {
   this.offset += 4;
-  this.ops.push(new WriteOp(CHECKSUM));
+  this.ops.push(new WriteOp(CHECKSUM, hash));
 };
 
 /**
diff --git a/lib/wallet/wallet.js b/lib/wallet/wallet.js
index 50f28ac6..39e9be80 100644
--- a/lib/wallet/wallet.js
+++ b/lib/wallet/wallet.js
@@ -545,7 +545,7 @@ Wallet.prototype.getID = function getID() {
   b58.writeU8(0xbe);
   b58.writeU8(0x04);
   b58.writeBytes(hash);
-  b58.writeChecksum();
+  b58.writeChecksum(digest.hash256);
 
   return base58.encode(b58.render());
 };