Merge branch 'v2-prototype' into refactor/order-utils/for-v2

* v2-prototype: (45 commits)
  Check length before accessing indices, add awaitTransactionSuccess where needed, and rename function
  Add back before/after snapshots for each test
  Rename Signer to Wallet, rename GAS_ESTIMATE to GAS_LIMIT
  Make preSigned and allowedValidators mappings public
  Change names of signature types
  Fix formatting and tests
  Make AssetProxyId last byte of assetData
  Add signer to txHash, allow approveValidator to be used with executeTransaction
  Update Whitelist
  Fix Exchange interface
  Increase block gas limit
  Use last byte of signature as signature type
  Remove TxOrigin signature type, modify whitelist to use Validator signature type
  Update Whitelist contract with comments, also require maker to be whitelisted
  Fix build
  Add example whitelist contract and minimum tests
  Add sample whitelist contract
  Add TxOrigin signature type and rearrange order of types
  Add approveValidator function
  Add Validator signature type
  ...

# Conflicts:
#	packages/contracts/src/contracts/current/protocol/Exchange/MixinSignatureValidator.sol
#	packages/contracts/src/utils/types.ts
#	packages/contracts/test/exchange/transactions.ts
#	packages/order-utils/src/asset_proxy_utils.ts

32 files changed, 530 insertions, 174 deletions

diff --git a/packages/contracts/src/contracts/current/protocol/AssetProxy/ERC20Proxy.sol b/packages/contracts/src/contracts/current/protocol/AssetProxy/ERC20Proxy.sol
index ee0c66fdc..79824fbbb 100644
--- a/packages/contracts/src/contracts/current/protocol/AssetProxy/ERC20Proxy.sol
+++ b/packages/contracts/src/contracts/current/protocol/AssetProxy/ERC20Proxy.sol
@@ -47,21 +47,25 @@ contract ERC20Proxy is
         bytes memory assetMetadata,
         address from,
         address to,
-        uint256 amount)
+        uint256 amount
+    )
         internal
     {
         // Data must be intended for this proxy.
+        uint256 length = assetMetadata.length;
+
         require(
-            uint8(assetMetadata[0]) == PROXY_ID,
-            PROXY_ID_MISMATCH
+            length == 21,
+            INVALID_METADATA_LENGTH
         );
 
-        // Decode metadata.
         require(
-            assetMetadata.length == 21,
-            INVALID_METADATA_LENGTH
+            uint8(assetMetadata[length - 1]) == PROXY_ID,
+            PROXY_ID_MISMATCH
         );
-        address token = readAddress(assetMetadata, 1);
+
+        // Decode metadata.
+        address token = readAddress(assetMetadata, 0);
 
         // Transfer tokens.
         bool success = IERC20Token(token).transferFrom(from, to, amount);
diff --git a/packages/contracts/src/contracts/current/protocol/AssetProxy/ERC721Proxy.sol b/packages/contracts/src/contracts/current/protocol/AssetProxy/ERC721Proxy.sol
index 94aab9139..ace3570bc 100644
--- a/packages/contracts/src/contracts/current/protocol/AssetProxy/ERC721Proxy.sol
+++ b/packages/contracts/src/contracts/current/protocol/AssetProxy/ERC721Proxy.sol
@@ -47,12 +47,20 @@ contract ERC721Proxy is
         bytes memory assetMetadata,
         address from,
         address to,
-        uint256 amount)
+        uint256 amount
+    )
         internal
     {
         // Data must be intended for this proxy.
+        uint256 length = assetMetadata.length;
+
+        require(
+            length == 53,
+            INVALID_METADATA_LENGTH
+        );
+
         require(
-            uint8(assetMetadata[0]) == PROXY_ID,
+            uint8(assetMetadata[length - 1]) == PROXY_ID,
             PROXY_ID_MISMATCH
         );
 
@@ -63,12 +71,8 @@ contract ERC721Proxy is
         );
 
         // Decode metadata
-        require(
-            assetMetadata.length == 53,
-            INVALID_METADATA_LENGTH
-        );
-        address token = readAddress(assetMetadata, 1);
-        uint256 tokenId = readUint256(assetMetadata, 21);
+        address token = readAddress(assetMetadata, 0);
+        uint256 tokenId = readUint256(assetMetadata, 20);
 
         // Transfer token.
         // Either succeeds or throws.
diff --git a/packages/contracts/src/contracts/current/protocol/AssetProxy/MixinAssetProxy.sol b/packages/contracts/src/contracts/current/protocol/AssetProxy/MixinAssetProxy.sol
index 4ec31304f..4bd533148 100644
--- a/packages/contracts/src/contracts/current/protocol/AssetProxy/MixinAssetProxy.sol
+++ b/packages/contracts/src/contracts/current/protocol/AssetProxy/MixinAssetProxy.sol
@@ -36,7 +36,8 @@ contract MixinAssetProxy is
         bytes assetMetadata,
         address from,
         address to,
-        uint256 amount)
+        uint256 amount
+    )
         external
         onlyAuthorized
     {
@@ -57,7 +58,8 @@ contract MixinAssetProxy is
         bytes[] memory assetMetadata,
         address[] memory from,
         address[] memory to,
-        uint256[] memory amounts)
+        uint256[] memory amounts
+    )
         public
         onlyAuthorized
     {
diff --git a/packages/contracts/src/contracts/current/protocol/AssetProxy/MixinAuthorizable.sol b/packages/contracts/src/contracts/current/protocol/AssetProxy/MixinAuthorizable.sol
index 0bbd3b318..4aaeb66d1 100644
--- a/packages/contracts/src/contracts/current/protocol/AssetProxy/MixinAuthorizable.sol
+++ b/packages/contracts/src/contracts/current/protocol/AssetProxy/MixinAuthorizable.sol
@@ -87,7 +87,10 @@ contract MixinAuthorizable is
     /// @dev Removes authorizion of an address.
     /// @param target Address to remove authorization from.
     /// @param index Index of target in authorities array.
-    function removeAuthorizedAddressAtIndex(address target, uint256 index)
+    function removeAuthorizedAddressAtIndex(
+        address target,
+        uint256 index
+    )
         external
     {
         require(
diff --git a/packages/contracts/src/contracts/current/protocol/AssetProxy/interfaces/IAssetProxy.sol b/packages/contracts/src/contracts/current/protocol/AssetProxy/interfaces/IAssetProxy.sol
index 8b30dfabb..7e1848889 100644
--- a/packages/contracts/src/contracts/current/protocol/AssetProxy/interfaces/IAssetProxy.sol
+++ b/packages/contracts/src/contracts/current/protocol/AssetProxy/interfaces/IAssetProxy.sol
@@ -34,7 +34,8 @@ contract IAssetProxy is
         bytes assetMetadata,
         address from,
         address to,
-        uint256 amount)
+        uint256 amount
+    )
         external;
     
     /// @dev Makes multiple transfers of assets. Either succeeds or throws.
@@ -46,7 +47,8 @@ contract IAssetProxy is
         bytes[] memory assetMetadata,
         address[] memory from,
         address[] memory to,
-        uint256[] memory amounts)
+        uint256[] memory amounts
+    )
         public;
 
     /// @dev Gets the proxy id associated with the proxy address.
diff --git a/packages/contracts/src/contracts/current/protocol/AssetProxy/interfaces/IAuthorizable.sol b/packages/contracts/src/contracts/current/protocol/AssetProxy/interfaces/IAuthorizable.sol
index d6fe03898..cedd1744c 100644
--- a/packages/contracts/src/contracts/current/protocol/AssetProxy/interfaces/IAuthorizable.sol
+++ b/packages/contracts/src/contracts/current/protocol/AssetProxy/interfaces/IAuthorizable.sol
@@ -45,6 +45,9 @@ contract IAuthorizable is
     /// @dev Removes authorizion of an address.
     /// @param target Address to remove authorization from.
     /// @param index Index of target in authorities array.
-    function removeAuthorizedAddressAtIndex(address target, uint256 index)
+    function removeAuthorizedAddressAtIndex(
+        address target,
+        uint256 index
+    )
         external;
 }
diff --git a/packages/contracts/src/contracts/current/protocol/AssetProxy/mixins/MAssetProxy.sol b/packages/contracts/src/contracts/current/protocol/AssetProxy/mixins/MAssetProxy.sol
index 3800bf04c..de9d65a53 100644
--- a/packages/contracts/src/contracts/current/protocol/AssetProxy/mixins/MAssetProxy.sol
+++ b/packages/contracts/src/contracts/current/protocol/AssetProxy/mixins/MAssetProxy.sol
@@ -34,6 +34,7 @@ contract MAssetProxy is
         bytes memory assetMetadata,
         address from,
         address to,
-        uint256 amount)
+        uint256 amount
+    )
         internal;
 }
diff --git a/packages/contracts/src/contracts/current/protocol/AssetProxy/mixins/MAuthorizable.sol b/packages/contracts/src/contracts/current/protocol/AssetProxy/mixins/MAuthorizable.sol
index cdf60bdee..6f35bd7ec 100644
--- a/packages/contracts/src/contracts/current/protocol/AssetProxy/mixins/MAuthorizable.sol
+++ b/packages/contracts/src/contracts/current/protocol/AssetProxy/mixins/MAuthorizable.sol
@@ -38,5 +38,5 @@ contract MAuthorizable is
     );
 
     /// @dev Only authorized addresses can invoke functions with this modifier.
-    modifier onlyAuthorized { _; }
+    modifier onlyAuthorized { revert(); _; }
 }
diff --git a/packages/contracts/src/contracts/current/protocol/Exchange/MixinAssetProxyDispatcher.sol b/packages/contracts/src/contracts/current/protocol/Exchange/MixinAssetProxyDispatcher.sol
index 3b38d1f37..d996f933c 100644
--- a/packages/contracts/src/contracts/current/protocol/Exchange/MixinAssetProxyDispatcher.sol
+++ b/packages/contracts/src/contracts/current/protocol/Exchange/MixinAssetProxyDispatcher.sol
@@ -39,7 +39,8 @@ contract MixinAssetProxyDispatcher is
     function registerAssetProxy(
         uint8 assetProxyId,
         address newAssetProxy,
-        address oldAssetProxy)
+        address oldAssetProxy
+    )
         external
         onlyOwner
     {
@@ -86,17 +87,20 @@ contract MixinAssetProxyDispatcher is
         bytes memory assetMetadata,
         address from,
         address to,
-        uint256 amount)
+        uint256 amount
+    )
         internal
     {
         // Do nothing if no amount should be transferred.
         if (amount > 0) {
+
             // Lookup asset proxy
+            uint256 length = assetMetadata.length;
             require(
-                assetMetadata.length >= 1,
+                length > 0,
                 GT_ZERO_LENGTH_REQUIRED
             );
-            uint8 assetProxyId = uint8(assetMetadata[0]);
+            uint8 assetProxyId = uint8(assetMetadata[length - 1]);
             IAssetProxy assetProxy = assetProxies[assetProxyId];
 
             // transferFrom will either succeed or throw.
diff --git a/packages/contracts/src/contracts/current/protocol/Exchange/MixinSignatureValidator.sol b/packages/contracts/src/contracts/current/protocol/Exchange/MixinSignatureValidator.sol
index af1199f66..79dc87af0 100644
--- a/packages/contracts/src/contracts/current/protocol/Exchange/MixinSignatureValidator.sol
+++ b/packages/contracts/src/contracts/current/protocol/Exchange/MixinSignatureValidator.sol
@@ -19,18 +19,24 @@
 pragma solidity ^0.4.24;
 
 import "./mixins/MSignatureValidator.sol";
-import "./interfaces/ISigner.sol";
+import "./mixins/MTransactions.sol";
+import "./interfaces/IWallet.sol";
+import "./interfaces/IValidator.sol";
 import "./libs/LibExchangeErrors.sol";
 import "../../utils/LibBytes/LibBytes.sol";
 
 contract MixinSignatureValidator is
     LibBytes,
     LibExchangeErrors,
-    MSignatureValidator
+    MSignatureValidator,
+    MTransactions
 {
 
     // Mapping of hash => signer => signed
-    mapping(bytes32 => mapping(address => bool)) public preSigned;
+    mapping (bytes32 => mapping (address => bool)) public preSigned;
+
+    // Mapping of signer => validator => approved
+    mapping (address => mapping (address => bool)) public allowedValidators;
 
     /// @dev Approves a hash on-chain using any valid signature type.
     ///      After presigning a hash, the preSign signature type will become valid for that hash and signer.
@@ -39,7 +45,8 @@ contract MixinSignatureValidator is
     function preSign(
         bytes32 hash,
         address signer,
-        bytes signature)
+        bytes signature
+    )
         external
     {
         require(
@@ -49,6 +56,19 @@ contract MixinSignatureValidator is
         preSigned[hash][signer] = true;
     }
 
+    /// @dev Approves/unnapproves a Validator contract to verify signatures on signer's behalf.
+    /// @param validator Address of Validator contract.
+    /// @param approval Approval or disapproval of  Validator contract.
+    function setSignatureValidatorApproval(
+        address validator,
+        bool approval
+    )
+        external
+    {
+        address signer = getCurrentContextAddress();
+        allowedValidators[signer][validator] = approval;
+    }
+
     /// @dev Verifies that a hash has been signed by the given signer.
     /// @param hash Any 32 byte hash.
     /// @param signer Address that should have signed the given hash.
@@ -57,71 +77,69 @@ contract MixinSignatureValidator is
     function isValidSignature(
         bytes32 hash,
         address signer,
-        bytes memory signature)
+        bytes memory signature
+    )
         internal
         view
         returns (bool isValid)
     {
         // TODO: Domain separation: make hash depend on role. (Taker sig should not be valid as maker sig, etc.)
-
         require(
             signature.length >= 1,
             INVALID_SIGNATURE_LENGTH
         );
-        SignatureType signatureType = SignatureType(uint8(signature[0]));
 
-        // Variables are not scoped in Solidity
+        // Pop last byte off of signature byte array.
+        SignatureType signatureType = SignatureType(uint8(popByte(signature)));
+
+        // Variables are not scoped in Solidity.
         uint8 v;
         bytes32 r;
         bytes32 s;
         address recovered;
 
-        // Always illegal signature
+        // Always illegal signature.
         // This is always an implicit option since a signer can create a
         // signature array with invalid type or length. We may as well make
         // it an explicit option. This aids testing and analysis. It is
         // also the initialization value for the enum type.
         if (signatureType == SignatureType.Illegal) {
-            // NOTE: Reason cannot be assigned to a variable because of https://github.com/ethereum/solidity/issues/4051
-            revert("Illegal signature type.");
+            revert(ILLEGAL_SIGNATURE_TYPE);
 
-        // Always invalid signature
+        // Always invalid signature.
         // Like Illegal, this is always implicitly available and therefore
         // offered explicitly. It can be implicitly created by providing
         // a correctly formatted but incorrect signature.
         } else if (signatureType == SignatureType.Invalid) {
             require(
-                signature.length == 1,
+                signature.length == 0,
                 INVALID_SIGNATURE_LENGTH
             );
             isValid = false;
             return isValid;
 
-        // Implicitly signed by caller
-        // The signer has initiated the call. In the case of non-contract
-        // accounts it means the transaction itself was signed.
-        // Example: let's say for a particular operation three signatures
-        // A, B and C are required. To submit the transaction, A and B can
-        // give a signature to C, who can then submit the transaction using
-        // `Caller` for his own signature. Or A and C can sign and B can
-        // submit using `Caller`. Having `Caller` allows this flexibility.
-        } else if (signatureType == SignatureType.Caller) {
+        // Signature using EIP712
+        } else if (signatureType == SignatureType.EIP712) {
             require(
-                signature.length == 1,
+                signature.length == 65,
                 INVALID_SIGNATURE_LENGTH
             );
-            isValid = signer == msg.sender;
+            v = uint8(signature[0]);
+            r = readBytes32(signature, 1);
+            s = readBytes32(signature, 33);
+            recovered = ecrecover(hash, v, r, s);
+            isValid = signer == recovered;
             return isValid;
 
         // Signed using web3.eth_sign
-        } else if (signatureType == SignatureType.Ecrecover) {
+        } else if (signatureType == SignatureType.EthSign) {
             require(
-                signature.length == 66,
+                signature.length == 65,
                 INVALID_SIGNATURE_LENGTH
             );
-            v = uint8(signature[1]);
-            r = readBytes32(signature, 2);
-            s = readBytes32(signature, 34);
+            v = uint8(signature[0]);
+            r = readBytes32(signature, 1);
+            s = readBytes32(signature, 33);
             recovered = ecrecover(
                 keccak256("\x19Ethereum Signed Message:\n32", hash),
                 v,
@@ -131,20 +149,55 @@ contract MixinSignatureValidator is
             isValid = signer == recovered;
             return isValid;
 
-        // Signature using EIP712
-        } else if (signatureType == SignatureType.EIP712) {
+        // Implicitly signed by caller.
+        // The signer has initiated the call. In the case of non-contract
+        // accounts it means the transaction itself was signed.
+        // Example: let's say for a particular operation three signatures
+        // A, B and C are required. To submit the transaction, A and B can
+        // give a signature to C, who can then submit the transaction using
+        // `Caller` for his own signature. Or A and C can sign and B can
+        // submit using `Caller`. Having `Caller` allows this flexibility.
+        } else if (signatureType == SignatureType.Caller) {
             require(
-                signature.length == 66,
+                signature.length == 0,
                 INVALID_SIGNATURE_LENGTH
             );
-            v = uint8(signature[1]);
-            r = readBytes32(signature, 2);
-            s = readBytes32(signature, 34);
-            recovered = ecrecover(hash, v, r, s);
-            isValid = signer == recovered;
+            isValid = signer == msg.sender;
             return isValid;
 
-        // Signature from Trezor hardware wallet
+        // Signature verified by wallet contract.
+        // If used with an order, the maker of the order is the wallet contract.
+        } else if (signatureType == SignatureType.Wallet) {
+            isValid = IWallet(signer).isValidSignature(hash, signature);
+            return isValid;
+
+        // Signature verified by validator contract.
+        // If used with an order, the maker of the order can still be an EOA.
+        // A signature using this type should be encoded as:
+        // | Offset   | Length | Contents                        |
+        // | 0x00     | x      | Signature to validate           |
+        // | 0x00 + x | 20     | Address of validator contract   |
+        // | 0x14 + x | 1      | Signature type is always "\x06" |
+        } else if (signatureType == SignatureType.Validator) {
+            // Pop last 20 bytes off of signature byte array.
+            address validator = popAddress(signature);
+            // Ensure signer has approved validator.
+            if (!allowedValidators[signer][validator]) {
+                return false;
+            }
+            isValid = IValidator(validator).isValidSignature(
+                hash,
+                signer,
+                signature
+            );
+            return isValid;
+
+        // Signer signed hash previously using the preSign function.
+        } else if (signatureType == SignatureType.PreSigned) {
+            isValid = preSigned[hash][signer];
+            return isValid;
+
+        // Signature from Trezor hardware wallet.
         // It differs from web3.eth_sign in the encoding of message length
         // (Bitcoin varint encoding vs ascii-decimal, the latter is not
         // self-terminating which leads to ambiguities).
@@ -154,12 +207,12 @@ contract MixinSignatureValidator is
         // https://github.com/trezor/trezor-mcu/blob/master/firmware/crypto.c#L36
         } else if (signatureType == SignatureType.Trezor) {
             require(
-                signature.length == 66,
+                signature.length == 65,
                 INVALID_SIGNATURE_LENGTH
             );
-            v = uint8(signature[1]);
-            r = readBytes32(signature, 2);
-            s = readBytes32(signature, 34);
+            v = uint8(signature[0]);
+            r = readBytes32(signature, 1);
+            s = readBytes32(signature, 33);
             recovered = ecrecover(
                 keccak256("\x19Ethereum Signed Message:\n\x41", hash),
                 v,
@@ -169,11 +222,6 @@ contract MixinSignatureValidator is
             isValid = signer == recovered;
             return isValid;
 
-        // Signature verified by signer contract
-        } else if (signatureType == SignatureType.Contract) {
-            isValid = ISigner(signer).isValidSignature(hash, signature);
-            return isValid;
-
         // Signer signed hash previously using the preSign function
         } else if (signatureType == SignatureType.PreSigned) {
             isValid = preSigned[hash][signer];
@@ -185,7 +233,6 @@ contract MixinSignatureValidator is
         // that we currently support. In this case returning false
         // may lead the caller to incorrectly believe that the
         // signature was invalid.)
-        // NOTE: Reason cannot be assigned to a variable because of https://github.com/ethereum/solidity/issues/4051
-        revert("Unsupported signature type.");
+        revert(UNSUPPORTED_SIGNATURE_TYPE);
     }
 }
diff --git a/packages/contracts/src/contracts/current/protocol/Exchange/MixinTransactions.sol b/packages/contracts/src/contracts/current/protocol/Exchange/MixinTransactions.sol
index f93a80705..d153dfa5c 100644
--- a/packages/contracts/src/contracts/current/protocol/Exchange/MixinTransactions.sol
+++ b/packages/contracts/src/contracts/current/protocol/Exchange/MixinTransactions.sol
@@ -43,15 +43,20 @@ contract MixinTransactions is
         uint256 salt,
         address signer,
         bytes data,
-        bytes signature)
+        bytes signature
+    )
         external
     {
         // Prevent reentrancy
-        require(currentContextAddress == address(0));
+        require(
+            currentContextAddress == address(0),
+            REENTRANCY_NOT_ALLOWED
+        );
 
         // Calculate transaction hash
         bytes32 transactionHash = keccak256(
             address(this),
+            signer,
             salt,
             data
         );
diff --git a/packages/contracts/src/contracts/current/protocol/Exchange/interfaces/IExchange.sol b/packages/contracts/src/contracts/current/protocol/Exchange/interfaces/IExchange.sol
index fc428e9c0..9f21c18d7 100644
--- a/packages/contracts/src/contracts/current/protocol/Exchange/interfaces/IExchange.sol
+++ b/packages/contracts/src/contracts/current/protocol/Exchange/interfaces/IExchange.sol
@@ -20,17 +20,15 @@ pragma solidity ^0.4.24;
 pragma experimental ABIEncoderV2;
 
 import "./IExchangeCore.sol";
-import "./IMatchOrders";
-import "./ISettlement";
-import "./ISignatureValidator";
-import "./ITransactions";
-import "./IAssetProxyDispatcher";
-import "./IWrapperFunctions";
+import "./IMatchOrders.sol";
+import "./ISignatureValidator.sol";
+import "./ITransactions.sol";
+import "./IAssetProxyDispatcher.sol";
+import "./IWrapperFunctions.sol";
 
 contract IExchange is
     IExchangeCore,
     IMatchOrders,
-    ISettlement,
     ISignatureValidator,
     ITransactions,
     IAssetProxyDispatcher,
diff --git a/packages/contracts/src/contracts/current/protocol/Exchange/interfaces/ISignatureValidator.sol b/packages/contracts/src/contracts/current/protocol/Exchange/interfaces/ISignatureValidator.sol
index 65ff45f7b..26e360c91 100644
--- a/packages/contracts/src/contracts/current/protocol/Exchange/interfaces/ISignatureValidator.sol
+++ b/packages/contracts/src/contracts/current/protocol/Exchange/interfaces/ISignatureValidator.sol
@@ -27,6 +27,16 @@ contract ISignatureValidator {
     function preSign(
         bytes32 hash,
         address signer,
-        bytes signature)
+        bytes signature
+    )
+        external;
+    
+    /// @dev Approves/unnapproves a Validator contract to verify signatures on signer's behalf.
+    /// @param validator Address of Validator contract.
+    /// @param approval Approval or disapproval of  Validator contract.
+    function setSignatureValidatorApproval(
+        address validator,
+        bool approval
+    )
         external;
 }
diff --git a/packages/contracts/src/contracts/current/protocol/Exchange/interfaces/IValidator.sol b/packages/contracts/src/contracts/current/protocol/Exchange/interfaces/IValidator.sol
new file mode 100644
index 000000000..3e5ccc190
--- /dev/null
+++ b/packages/contracts/src/contracts/current/protocol/Exchange/interfaces/IValidator.sol
@@ -0,0 +1,36 @@
+/*
+
+  Copyright 2018 ZeroEx Intl.
+
+  Licensed under the Apache License, Version 2.0 (the "License");
+  you may not use this file except in compliance with the License.
+  You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing, software
+  distributed under the License is distributed on an "AS IS" BASIS,
+  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  See the License for the specific language governing permissions and
+  limitations under the License.
+
+*/
+
+pragma solidity ^0.4.23;
+
+contract IValidator {
+
+    /// @dev Verifies that a signature is valid.
+    /// @param hash Message hash that is signed.
+    /// @param signer Address that should have signed the given hash.
+    /// @param signature Proof of signing.
+    /// @return Validity of order signature.
+    function isValidSignature(
+        bytes32 hash,
+        address signer,
+        bytes signature
+    )
+        external
+        view
+        returns (bool isValid);
+}
diff --git a/packages/contracts/src/contracts/current/protocol/Exchange/interfaces/ISigner.sol b/packages/contracts/src/contracts/current/protocol/Exchange/interfaces/IWallet.sol
index 53c41d331..c86a2c057 100644
--- a/packages/contracts/src/contracts/current/protocol/Exchange/interfaces/ISigner.sol
+++ b/packages/contracts/src/contracts/current/protocol/Exchange/interfaces/IWallet.sol
@@ -18,7 +18,7 @@
 
 pragma solidity ^0.4.24;
 
-contract ISigner {
+contract IWallet {
 
     /// @dev Verifies that a signature is valid.
     /// @param hash Message hash that is signed.
@@ -26,7 +26,8 @@ contract ISigner {
     /// @return Validity of order signature.
     function isValidSignature(
         bytes32 hash,
-        bytes signature)
+        bytes signature
+    )
         external
         view
         returns (bool isValid);
diff --git a/packages/contracts/src/contracts/current/protocol/Exchange/interfaces/IWrapperFunctions.sol b/packages/contracts/src/contracts/current/protocol/Exchange/interfaces/IWrapperFunctions.sol
index 1eb1233ed..8682b394a 100644
--- a/packages/contracts/src/contracts/current/protocol/Exchange/interfaces/IWrapperFunctions.sol
+++ b/packages/contracts/src/contracts/current/protocol/Exchange/interfaces/IWrapperFunctions.sol
@@ -19,27 +19,23 @@
 pragma solidity ^0.4.24;
 pragma experimental ABIEncoderV2;
 
-import "./libs/LibOrder.sol";
-import "./libs/LibFillResults.sol";
+import "../libs/LibOrder.sol";
+import "../libs/LibFillResults.sol";
 
 contract IWrapperFunctions is
-    LibBytes,
-    LibMath,
     LibOrder,
-    LibFillResults,
-    LibExchangeErrors,
-    MExchangeCore
+    LibFillResults
 {
     /// @dev Fills the input order. Reverts if exact takerAssetFillAmount not filled.
     /// @param order LibOrder.Order struct containing order specifications.
     /// @param takerAssetFillAmount Desired amount of takerAsset to sell.
     /// @param signature Proof that order has been created by maker.
     function fillOrKillOrder(
-        LibOrder.LibOrder.Order memory order,
+        LibOrder.Order memory order,
         uint256 takerAssetFillAmount,
         bytes memory signature)
         public
-        returns (LibFillResults.LibFillResults.FillResults memory fillResults);
+        returns (LibFillResults.FillResults memory fillResults);
 
     /// @dev Fills an order with specified parameters and ECDSA signature.
     ///      Returns false if the transaction would otherwise revert.
diff --git a/packages/contracts/src/contracts/current/protocol/Exchange/libs/LibExchangeErrors.sol b/packages/contracts/src/contracts/current/protocol/Exchange/libs/LibExchangeErrors.sol
index 4712ee36c..7d67e5080 100644
--- a/packages/contracts/src/contracts/current/protocol/Exchange/libs/LibExchangeErrors.sol
+++ b/packages/contracts/src/contracts/current/protocol/Exchange/libs/LibExchangeErrors.sol
@@ -32,6 +32,7 @@ contract LibExchangeErrors {
     string constant INVALID_ORDER_MAKER_ASSET_AMOUNT = "Invalid order maker asset amount: expected a non-zero value.";
 
     // Transaction revert reasons
+    string constant REENTRANCY_NOT_ALLOWED = "`executeTransaction` is not allowed to call itself recursively.";
     string constant DUPLICATE_TRANSACTION_HASH = "Transaction has already been executed.";
     string constant TRANSACTION_EXECUTION_FAILED = "Transaction execution failed.";
 
diff --git a/packages/contracts/src/contracts/current/protocol/Exchange/mixins/MAssetProxyDispatcher.sol b/packages/contracts/src/contracts/current/protocol/Exchange/mixins/MAssetProxyDispatcher.sol
index ccc960d6e..87c5f6361 100644
--- a/packages/contracts/src/contracts/current/protocol/Exchange/mixins/MAssetProxyDispatcher.sol
+++ b/packages/contracts/src/contracts/current/protocol/Exchange/mixins/MAssetProxyDispatcher.sol
@@ -41,6 +41,7 @@ contract MAssetProxyDispatcher is
         bytes memory assetMetadata,
         address from,
         address to,
-        uint256 amount)
+        uint256 amount
+    )
         internal;
 }
diff --git a/packages/contracts/src/contracts/current/protocol/Exchange/mixins/MSignatureValidator.sol b/packages/contracts/src/contracts/current/protocol/Exchange/mixins/MSignatureValidator.sol
index 3658e7c6f..7eed453ff 100644
--- a/packages/contracts/src/contracts/current/protocol/Exchange/mixins/MSignatureValidator.sol
+++ b/packages/contracts/src/contracts/current/protocol/Exchange/mixins/MSignatureValidator.sol
@@ -25,14 +25,15 @@ contract MSignatureValidator is
 {
     // Allowed signature types.
     enum SignatureType {
-        Illegal,  // Default value
-        Invalid,
-        Caller,
-        Ecrecover,
-        EIP712,
-        Trezor,
-        Contract,
-        PreSigned
+        Illegal,    // 0x00, default value
+        Invalid,    // 0x01
+        EIP712,     // 0x02
+        EthSign,    // 0x03
+        Caller,     // 0x04
+        Wallet,     // 0x05
+        Validator,  // 0x06
+        PreSigned,  // 0x07
+        Trezor      // 0x08
     }
 
     /// @dev Verifies that a signature is valid.
@@ -43,7 +44,8 @@ contract MSignatureValidator is
     function isValidSignature(
         bytes32 hash,
         address signer,
-        bytes memory signature)
+        bytes memory signature
+    )
         internal
         view
         returns (bool isValid);
diff --git a/packages/contracts/src/contracts/current/test/TestLibBytes/TestLibBytes.sol b/packages/contracts/src/contracts/current/test/TestLibBytes/TestLibBytes.sol
index 5a6801262..69554605d 100644
--- a/packages/contracts/src/contracts/current/test/TestLibBytes/TestLibBytes.sol
+++ b/packages/contracts/src/contracts/current/test/TestLibBytes/TestLibBytes.sol
@@ -25,6 +25,30 @@ contract TestLibBytes is
     LibBytes
 {
 
+    /// @dev Pops the last byte off of a byte array by modifying its length.
+    /// @param b Byte array that will be modified.
+    /// @return The byte that was popped off.
+    function publicPopByte(bytes memory b)
+        public
+        pure
+        returns (bytes memory, bytes1 result)
+    {
+        result = popByte(b);
+        return (b, result);
+    }
+
+    /// @dev Pops the last 20 bytes off of a byte array by modifying its length.
+    /// @param b Byte array that will be modified.
+    /// @return The 20 byte address that was popped off.
+    function publicPopAddress(bytes memory b)
+        public
+        pure
+        returns (bytes memory, address result)
+    {
+        result = popAddress(b);
+        return (b, result);
+    }
+
     /// @dev Tests equality of two byte arrays.
     /// @param lhs First byte array to compare.
     /// @param rhs Second byte array to compare.
diff --git a/packages/contracts/src/contracts/current/test/TestSignatureValidator/TestSignatureValidator.sol b/packages/contracts/src/contracts/current/test/TestSignatureValidator/TestSignatureValidator.sol
index 15d9ca189..0f84678cf 100644
--- a/packages/contracts/src/contracts/current/test/TestSignatureValidator/TestSignatureValidator.sol
+++ b/packages/contracts/src/contracts/current/test/TestSignatureValidator/TestSignatureValidator.sol
@@ -20,13 +20,18 @@ pragma solidity ^0.4.24;
 pragma experimental ABIEncoderV2;
 
 import "../../protocol/Exchange/MixinSignatureValidator.sol";
+import "../../protocol/Exchange/MixinTransactions.sol";
 
-contract TestSignatureValidator is MixinSignatureValidator {
+contract TestSignatureValidator is
+    MixinSignatureValidator,
+    MixinTransactions
+{
 
     function publicIsValidSignature(
         bytes32 hash,
         address signer,
-        bytes memory signature)
+        bytes memory signature
+    )
         public
         view
         returns (bool isValid)
diff --git a/packages/contracts/src/contracts/current/test/Whitelist/Whitelist.sol b/packages/contracts/src/contracts/current/test/Whitelist/Whitelist.sol
new file mode 100644
index 000000000..0594e2767
--- /dev/null
+++ b/packages/contracts/src/contracts/current/test/Whitelist/Whitelist.sol
@@ -0,0 +1,133 @@
+/*
+
+  Copyright 2018 ZeroEx Intl.
+
+  Licensed under the Apache License, Version 2.0 (the "License");
+  you may not use this file except in compliance with the License.
+  You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing, software
+  distributed under the License is distributed on an "AS IS" BASIS,
+  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  See the License for the specific language governing permissions and
+  limitations under the License.
+
+*/
+
+pragma solidity ^0.4.23;
+pragma experimental ABIEncoderV2;
+
+import "../../protocol/Exchange/interfaces/IExchange.sol";
+import "../../protocol/Exchange/libs/LibOrder.sol";
+import "../../utils/Ownable/Ownable.sol";
+
+contract Whitelist is 
+    Ownable
+{
+    // Revert reasons
+    string constant MAKER_NOT_WHITELISTED = "Maker address not whitelisted.";
+    string constant TAKER_NOT_WHITELISTED = "Taker address not whitelisted.";
+    string constant INVALID_SENDER = "Sender must equal transaction origin.";
+
+    // Mapping of address => whitelist status.
+    mapping (address => bool) public isWhitelisted;
+
+    // Exchange contract.
+    IExchange EXCHANGE;
+
+    byte constant VALIDATOR_SIGNATURE_BYTE = "\x06";
+    bytes TX_ORIGIN_SIGNATURE;
+
+    constructor (address _exchange)
+        public
+    {
+        EXCHANGE = IExchange(_exchange);
+        TX_ORIGIN_SIGNATURE = abi.encodePacked(address(this), VALIDATOR_SIGNATURE_BYTE);
+    }
+
+    /// @dev Adds or removes an address from the whitelist.
+    /// @param target Address to add or remove from whitelist.
+    /// @param isApproved Whitelist status to assign to address.
+    function updateWhitelistStatus(
+        address target,
+        bool isApproved
+    )
+        external
+        onlyOwner
+    {
+        isWhitelisted[target] = isApproved;
+    }
+
+    /// @dev Fills an order using `msg.sender` as the taker.
+    ///      The transaction will revert if both the maker and taker are not whitelisted.
+    ///      Orders should specify this contract as the `senderAddress` in order to gaurantee
+    ///      that both maker and taker have been whitelisted.
+    /// @param order Order struct containing order specifications.
+    /// @param takerAssetFillAmount Desired amount of takerAsset to sell.
+    /// @param salt Arbitrary value to gaurantee uniqueness of 0x transaction hash.
+    /// @param orderSignature Proof that order has been created by maker.
+    function fillOrderIfWhitelisted(
+        LibOrder.Order memory order,
+        uint256 takerAssetFillAmount,
+        uint256 salt,
+        bytes memory orderSignature
+    )
+        public
+    {
+        address takerAddress = msg.sender;
+    
+        // This contract must be the entry point for the transaction.
+        require(
+            takerAddress == tx.origin,
+            INVALID_SENDER
+        );
+
+        // Check if maker is on the whitelist.
+        require(
+            isWhitelisted[order.makerAddress],
+            MAKER_NOT_WHITELISTED
+        );
+
+        // Check if taker is on the whitelist.
+        require(
+            isWhitelisted[takerAddress],
+            TAKER_NOT_WHITELISTED
+        );
+
+        // Encode arguments into byte array.
+        bytes memory data = abi.encodeWithSelector(
+            EXCHANGE.fillOrder.selector,
+            order,
+            takerAssetFillAmount,
+            orderSignature
+        );
+
+        // Call `fillOrder` via `executeTransaction`.
+        EXCHANGE.executeTransaction(
+            salt,
+            takerAddress,
+            data,
+            TX_ORIGIN_SIGNATURE
+        );
+    }
+
+    /// @dev Verifies signer is same as signer of current Ethereum transaction.
+    ///      NOTE: This function can currently be used to validate signatures coming from outside of this contract.
+    ///      Extra safety checks can be added for a production contract.
+    /// @param signer Address that should have signed the given hash.
+    /// @param signature Proof of signing.
+    /// @return Validity of order signature.
+    function isValidSignature(
+        bytes32 hash,
+        address signer,
+        bytes signature
+    )
+        external
+        view
+        returns (bool isValid)
+    {
+        return signer == tx.origin;
+    }
+}
diff --git a/packages/contracts/src/contracts/current/utils/LibBytes/LibBytes.sol b/packages/contracts/src/contracts/current/utils/LibBytes/LibBytes.sol
index 975565773..df2221c93 100644
--- a/packages/contracts/src/contracts/current/utils/LibBytes/LibBytes.sol
+++ b/packages/contracts/src/contracts/current/utils/LibBytes/LibBytes.sol
@@ -21,15 +21,68 @@ pragma solidity ^0.4.24;
 contract LibBytes {
 
     // Revert reasons
+    string constant GT_ZERO_LENGTH_REQUIRED = "Length must be greater than 0.";
     string constant GTE_4_LENGTH_REQUIRED = "Length must be greater than or equal to 4.";
     string constant GTE_20_LENGTH_REQUIRED = "Length must be greater than or equal to 20.";
     string constant GTE_32_LENGTH_REQUIRED = "Length must be greater than or equal to 32.";
+    string constant INDEX_OUT_OF_BOUNDS = "Specified array index is out of bounds.";
+
+    /// @dev Pops the last byte off of a byte array by modifying its length.
+    /// @param b Byte array that will be modified.
+    /// @return The byte that was popped off.
+    function popByte(bytes memory b)
+        internal
+        pure
+        returns (bytes1 result)
+    {
+        require(
+            b.length > 0,
+            GT_ZERO_LENGTH_REQUIRED
+        );
+
+        // Store last byte.
+        result = b[b.length - 1];
+        
+        assembly {
+            // Decrement length of byte array.
+            let newLen := sub(mload(b), 1)
+            mstore(b, newLen)
+        }
+        return result;
+    }
+
+    /// @dev Pops the last 20 bytes off of a byte array by modifying its length.
+    /// @param b Byte array that will be modified.
+    /// @return The 20 byte address that was popped off.
+    function popAddress(bytes memory b)
+        internal
+        pure
+        returns (address result)
+    {
+        require(
+            b.length >= 20,
+            GTE_20_LENGTH_REQUIRED
+        );
+
+        // Store last 20 bytes.
+        result = readAddress(b, b.length - 20);
+
+        assembly {
+            // Subtract 20 from byte array length.
+            let newLen := sub(mload(b), 20)
+            mstore(b, newLen)
+        }
+        return result;
+    }
 
     /// @dev Tests equality of two byte arrays.
     /// @param lhs First byte array to compare.
     /// @param rhs Second byte array to compare.
     /// @return True if arrays are the same. False otherwise.
-    function areBytesEqual(bytes memory lhs, bytes memory rhs)
+    function areBytesEqual(
+        bytes memory lhs,
+        bytes memory rhs
+    )
         internal
         pure
         returns (bool equal)
@@ -63,7 +116,8 @@ contract LibBytes {
     /// @return address from byte array.
     function readAddress(
         bytes memory b,
-        uint256 index)
+        uint256 index
+    )
         internal
         pure
         returns (address result)
@@ -95,7 +149,8 @@ contract LibBytes {
     function writeAddress(
         bytes memory b,
         uint256 index,
-        address input)
+        address input
+    )
         internal
         pure
     {
@@ -132,7 +187,8 @@ contract LibBytes {
     /// @return bytes32 value from byte array.
     function readBytes32(
         bytes memory b,
-        uint256 index)
+        uint256 index
+    )
         internal
         pure
         returns (bytes32 result)
@@ -159,7 +215,8 @@ contract LibBytes {
     function writeBytes32(
         bytes memory b,
         uint256 index,
-        bytes32 input)
+        bytes32 input
+    )
         internal
         pure
     {
@@ -183,7 +240,8 @@ contract LibBytes {
     /// @return uint256 value from byte array.
     function readUint256(
         bytes memory b,
-        uint256 index)
+        uint256 index
+    )
         internal
         pure
         returns (uint256 result)
@@ -198,7 +256,8 @@ contract LibBytes {
     function writeUint256(
         bytes memory b,
         uint256 index,
-        uint256 input)
+        uint256 input
+    )
         internal
         pure
     {
diff --git a/packages/contracts/src/utils/artifacts.ts b/packages/contracts/src/utils/artifacts.ts
index fe74ea072..357c66a0a 100644
--- a/packages/contracts/src/utils/artifacts.ts
+++ b/packages/contracts/src/utils/artifacts.ts
@@ -15,6 +15,7 @@ import * as TestLibs from '../artifacts/TestLibs.json';
 import * as TestSignatureValidator from '../artifacts/TestSignatureValidator.json';
 import * as TokenRegistry from '../artifacts/TokenRegistry.json';
 import * as EtherToken from '../artifacts/WETH9.json';
+import * as Whitelist from '../artifacts/Whitelist.json';
 import * as ZRX from '../artifacts/ZRXToken.json';
 
 export const artifacts = {
@@ -33,5 +34,6 @@ export const artifacts = {
     TestLibs: (TestLibs as any) as ContractArtifact,
     TestSignatureValidator: (TestSignatureValidator as any) as ContractArtifact,
     TokenRegistry: (TokenRegistry as any) as ContractArtifact,
+    Whitelist: (Whitelist as any) as ContractArtifact,
     ZRX: (ZRX as any) as ContractArtifact,
 };
diff --git a/packages/contracts/src/utils/constants.ts b/packages/contracts/src/utils/constants.ts
index 7a0e26a48..9b0b92545 100644
--- a/packages/contracts/src/utils/constants.ts
+++ b/packages/contracts/src/utils/constants.ts
@@ -28,6 +28,7 @@ export const constants = {
     DUMMY_TOKEN_SYMBOL: '',
     DUMMY_TOKEN_DECIMALS: new BigNumber(18),
     DUMMY_TOKEN_TOTAL_SUPPLY: new BigNumber(0),
+    NULL_BYTES: '0x',
     NUM_DUMMY_ERC20_TO_DEPLOY: 3,
     NUM_DUMMY_ERC721_TO_DEPLOY: 1,
     NUM_ERC721_TOKENS_TO_MINT: 2,
diff --git a/packages/contracts/src/utils/exchange_wrapper.ts b/packages/contracts/src/utils/exchange_wrapper.ts
index f7bd207a4..8f5915d97 100644
--- a/packages/contracts/src/utils/exchange_wrapper.ts
+++ b/packages/contracts/src/utils/exchange_wrapper.ts
@@ -7,16 +7,18 @@ import { ExchangeContract } from '../contract_wrappers/generated/exchange';
 
 import { constants } from './constants';
 import { formatters } from './formatters';
-import { logDecoder } from './log_decoder';
+import { LogDecoder } from './log_decoder';
 import { orderUtils } from './order_utils';
 import { OrderInfo, SignedTransaction } from './types';
 
 export class ExchangeWrapper {
     private _exchange: ExchangeContract;
     private _web3Wrapper: Web3Wrapper;
+    private _logDecoder: LogDecoder;
     constructor(exchangeContract: ExchangeContract, provider: Provider) {
         this._exchange = exchangeContract;
         this._web3Wrapper = new Web3Wrapper(provider);
+        this._logDecoder = new LogDecoder(this._web3Wrapper, this._exchange.address);
     }
     public async fillOrderAsync(
         signedOrder: SignedOrder,
@@ -30,13 +32,13 @@ export class ExchangeWrapper {
             params.signature,
             { from },
         );
-        const tx = await this._getTxWithDecodedExchangeLogsAsync(txHash);
+        const tx = await this._logDecoder.getTxWithDecodedLogsAsync(txHash);
         return tx;
     }
     public async cancelOrderAsync(signedOrder: SignedOrder, from: string): Promise<TransactionReceiptWithDecodedLogs> {
         const params = orderUtils.createCancel(signedOrder);
         const txHash = await this._exchange.cancelOrder.sendTransactionAsync(params.order, { from });
-        const tx = await this._getTxWithDecodedExchangeLogsAsync(txHash);
+        const tx = await this._logDecoder.getTxWithDecodedLogsAsync(txHash);
         return tx;
     }
     public async fillOrKillOrderAsync(
@@ -51,7 +53,7 @@ export class ExchangeWrapper {
             params.signature,
             { from },
         );
-        const tx = await this._getTxWithDecodedExchangeLogsAsync(txHash);
+        const tx = await this._logDecoder.getTxWithDecodedLogsAsync(txHash);
         return tx;
     }
     public async fillOrderNoThrowAsync(
@@ -66,7 +68,7 @@ export class ExchangeWrapper {
             params.signature,
             { from },
         );
-        const tx = await this._getTxWithDecodedExchangeLogsAsync(txHash);
+        const tx = await this._logDecoder.getTxWithDecodedLogsAsync(txHash);
         return tx;
     }
     public async batchFillOrdersAsync(
@@ -81,7 +83,7 @@ export class ExchangeWrapper {
             params.signatures,
             { from },
         );
-        const tx = await this._getTxWithDecodedExchangeLogsAsync(txHash);
+        const tx = await this._logDecoder.getTxWithDecodedLogsAsync(txHash);
         return tx;
     }
     public async batchFillOrKillOrdersAsync(
@@ -96,7 +98,7 @@ export class ExchangeWrapper {
             params.signatures,
             { from },
         );
-        const tx = await this._getTxWithDecodedExchangeLogsAsync(txHash);
+        const tx = await this._logDecoder.getTxWithDecodedLogsAsync(txHash);
         return tx;
     }
     public async batchFillOrdersNoThrowAsync(
@@ -111,7 +113,7 @@ export class ExchangeWrapper {
             params.signatures,
             { from },
         );
-        const tx = await this._getTxWithDecodedExchangeLogsAsync(txHash);
+        const tx = await this._logDecoder.getTxWithDecodedLogsAsync(txHash);
         return tx;
     }
     public async marketSellOrdersAsync(
@@ -126,7 +128,7 @@ export class ExchangeWrapper {
             params.signatures,
             { from },
         );
-        const tx = await this._getTxWithDecodedExchangeLogsAsync(txHash);
+        const tx = await this._logDecoder.getTxWithDecodedLogsAsync(txHash);
         return tx;
     }
     public async marketSellOrdersNoThrowAsync(
@@ -141,7 +143,7 @@ export class ExchangeWrapper {
             params.signatures,
             { from },
         );
-        const tx = await this._getTxWithDecodedExchangeLogsAsync(txHash);
+        const tx = await this._logDecoder.getTxWithDecodedLogsAsync(txHash);
         return tx;
     }
     public async marketBuyOrdersAsync(
@@ -156,7 +158,7 @@ export class ExchangeWrapper {
             params.signatures,
             { from },
         );
-        const tx = await this._getTxWithDecodedExchangeLogsAsync(txHash);
+        const tx = await this._logDecoder.getTxWithDecodedLogsAsync(txHash);
         return tx;
     }
     public async marketBuyOrdersNoThrowAsync(
@@ -171,7 +173,7 @@ export class ExchangeWrapper {
             params.signatures,
             { from },
         );
-        const tx = await this._getTxWithDecodedExchangeLogsAsync(txHash);
+        const tx = await this._logDecoder.getTxWithDecodedLogsAsync(txHash);
         return tx;
     }
     public async batchCancelOrdersAsync(
@@ -180,12 +182,12 @@ export class ExchangeWrapper {
     ): Promise<TransactionReceiptWithDecodedLogs> {
         const params = formatters.createBatchCancel(orders);
         const txHash = await this._exchange.batchCancelOrders.sendTransactionAsync(params.orders, { from });
-        const tx = await this._getTxWithDecodedExchangeLogsAsync(txHash);
+        const tx = await this._logDecoder.getTxWithDecodedLogsAsync(txHash);
         return tx;
     }
     public async cancelOrdersUpToAsync(salt: BigNumber, from: string): Promise<TransactionReceiptWithDecodedLogs> {
         const txHash = await this._exchange.cancelOrdersUpTo.sendTransactionAsync(salt, { from });
-        const tx = await this._getTxWithDecodedExchangeLogsAsync(txHash);
+        const tx = await this._logDecoder.getTxWithDecodedLogsAsync(txHash);
         return tx;
     }
     public async registerAssetProxyAsync(
@@ -203,7 +205,7 @@ export class ExchangeWrapper {
             oldAssetProxyAddress,
             { from },
         );
-        const tx = await this._getTxWithDecodedExchangeLogsAsync(txHash);
+        const tx = await this._logDecoder.getTxWithDecodedLogsAsync(txHash);
         return tx;
     }
     public async executeTransactionAsync(
@@ -217,7 +219,7 @@ export class ExchangeWrapper {
             signedTx.signature,
             { from },
         );
-        const tx = await this._getTxWithDecodedExchangeLogsAsync(txHash);
+        const tx = await this._logDecoder.getTxWithDecodedLogsAsync(txHash);
         return tx;
     }
     public async getTakerAssetFilledAmountAsync(orderHashHex: string): Promise<BigNumber> {
@@ -241,13 +243,7 @@ export class ExchangeWrapper {
             params.rightSignature,
             { from },
         );
-        const tx = await this._getTxWithDecodedExchangeLogsAsync(txHash);
-        return tx;
-    }
-    private async _getTxWithDecodedExchangeLogsAsync(txHash: string): Promise<TransactionReceiptWithDecodedLogs> {
-        const tx = await this._web3Wrapper.awaitTransactionSuccessAsync(txHash, constants.AWAIT_TRANSACTION_MINED_MS);
-        tx.logs = _.filter(tx.logs, log => log.address === this._exchange.address);
-        tx.logs = _.map(tx.logs, log => logDecoder.decodeLogOrThrow(log));
+        const tx = await this._logDecoder.getTxWithDecodedLogsAsync(txHash);
         return tx;
     }
 }
diff --git a/packages/contracts/src/utils/log_decoder.ts b/packages/contracts/src/utils/log_decoder.ts
index d2e65d176..32819b657 100644
--- a/packages/contracts/src/utils/log_decoder.ts
+++ b/packages/contracts/src/utils/log_decoder.ts
@@ -1,19 +1,23 @@
 import { ContractArtifact } from '@0xproject/sol-compiler';
-import { AbiDefinition, LogEntry, LogWithDecodedArgs, RawLog } from '@0xproject/types';
+import {
+    AbiDefinition,
+    LogEntry,
+    LogWithDecodedArgs,
+    RawLog,
+    TransactionReceiptWithDecodedLogs,
+} from '@0xproject/types';
 import { AbiDecoder, BigNumber } from '@0xproject/utils';
+import { Web3Wrapper } from '@0xproject/web3-wrapper';
 import * as _ from 'lodash';
 
 import { artifacts } from './artifacts';
+import { constants } from './constants';
 
-const abiArrays: AbiDefinition[][] = [];
-_.forEach(artifacts, (artifact: ContractArtifact) => {
-    const compilerOutput = artifact.compilerOutput;
-    abiArrays.push(compilerOutput.abi);
-});
-const abiDecoder = new AbiDecoder(abiArrays);
-
-export const logDecoder = {
-    wrapLogBigNumbers(log: any): any {
+export class LogDecoder {
+    private _web3Wrapper: Web3Wrapper;
+    private _contractAddress: string;
+    private _abiDecoder: AbiDecoder;
+    public static wrapLogBigNumbers(log: any): any {
         const argNames = _.keys(log.args);
         for (const argName of argNames) {
             const isWeb3BigNumber = _.startsWith(log.args[argName].constructor.toString(), 'function BigNumber(');
@@ -21,13 +25,29 @@ export const logDecoder = {
                 log.args[argName] = new BigNumber(log.args[argName]);
             }
         }
-    },
-    decodeLogOrThrow<ArgsType>(log: LogEntry): LogWithDecodedArgs<ArgsType> | RawLog {
-        const logWithDecodedArgsOrLog = abiDecoder.tryToDecodeLogOrNoop(log);
+    }
+    constructor(web3Wrapper: Web3Wrapper, contractAddress: string) {
+        this._web3Wrapper = web3Wrapper;
+        this._contractAddress = contractAddress;
+        const abiArrays: AbiDefinition[][] = [];
+        _.forEach(artifacts, (artifact: ContractArtifact) => {
+            const compilerOutput = artifact.compilerOutput;
+            abiArrays.push(compilerOutput.abi);
+        });
+        this._abiDecoder = new AbiDecoder(abiArrays);
+    }
+    public decodeLogOrThrow<ArgsType>(log: LogEntry): LogWithDecodedArgs<ArgsType> | RawLog {
+        const logWithDecodedArgsOrLog = this._abiDecoder.tryToDecodeLogOrNoop(log);
         if (_.isUndefined((logWithDecodedArgsOrLog as LogWithDecodedArgs<ArgsType>).args)) {
             throw new Error(`Unable to decode log: ${JSON.stringify(log)}`);
         }
-        logDecoder.wrapLogBigNumbers(logWithDecodedArgsOrLog);
+        LogDecoder.wrapLogBigNumbers(logWithDecodedArgsOrLog);
         return logWithDecodedArgsOrLog;
-    },
-};
+    }
+    public async getTxWithDecodedLogsAsync(txHash: string): Promise<TransactionReceiptWithDecodedLogs> {
+        const tx = await this._web3Wrapper.awaitTransactionSuccessAsync(txHash, constants.AWAIT_TRANSACTION_MINED_MS);
+        tx.logs = _.filter(tx.logs, log => log.address === this._contractAddress);
+        tx.logs = _.map(tx.logs, log => this.decodeLogOrThrow(log));
+        return tx;
+    }
+}
diff --git a/packages/contracts/src/utils/multi_sig_wrapper.ts b/packages/contracts/src/utils/multi_sig_wrapper.ts
index 5c73cdf5a..d67692194 100644
--- a/packages/contracts/src/utils/multi_sig_wrapper.ts
+++ b/packages/contracts/src/utils/multi_sig_wrapper.ts
@@ -7,14 +7,16 @@ import { AssetProxyOwnerContract } from '../contract_wrappers/generated/asset_pr
 import { MultiSigWalletContract } from '../contract_wrappers/generated/multi_sig_wallet';
 
 import { constants } from './constants';
-import { logDecoder } from './log_decoder';
+import { LogDecoder } from './log_decoder';
 
 export class MultiSigWrapper {
     private _multiSig: MultiSigWalletContract;
     private _web3Wrapper: Web3Wrapper;
+    private _logDecoder: LogDecoder;
     constructor(multiSigContract: MultiSigWalletContract, provider: Provider) {
         this._multiSig = multiSigContract;
         this._web3Wrapper = new Web3Wrapper(provider);
+        this._logDecoder = new LogDecoder(this._web3Wrapper, this._multiSig.address);
     }
     public async submitTransactionAsync(
         destination: string,
@@ -26,17 +28,17 @@ export class MultiSigWrapper {
         const txHash = await this._multiSig.submitTransaction.sendTransactionAsync(destination, value, data, {
             from,
         });
-        const tx = await this._getTxWithDecodedMultiSigLogsAsync(txHash);
+        const tx = await this._logDecoder.getTxWithDecodedLogsAsync(txHash);
         return tx;
     }
     public async confirmTransactionAsync(txId: BigNumber, from: string): Promise<TransactionReceiptWithDecodedLogs> {
         const txHash = await this._multiSig.confirmTransaction.sendTransactionAsync(txId, { from });
-        const tx = await this._getTxWithDecodedMultiSigLogsAsync(txHash);
+        const tx = await this._logDecoder.getTxWithDecodedLogsAsync(txHash);
         return tx;
     }
     public async executeTransactionAsync(txId: BigNumber, from: string): Promise<TransactionReceiptWithDecodedLogs> {
         const txHash = await this._multiSig.executeTransaction.sendTransactionAsync(txId, { from });
-        const tx = await this._getTxWithDecodedMultiSigLogsAsync(txHash);
+        const tx = await this._logDecoder.getTxWithDecodedLogsAsync(txHash);
         return tx;
     }
     public async executeRemoveAuthorizedAddressAsync(
@@ -45,13 +47,7 @@ export class MultiSigWrapper {
     ): Promise<TransactionReceiptWithDecodedLogs> {
         const txHash = await (this
             ._multiSig as AssetProxyOwnerContract).executeRemoveAuthorizedAddress.sendTransactionAsync(txId, { from });
-        const tx = await this._getTxWithDecodedMultiSigLogsAsync(txHash);
-        return tx;
-    }
-    private async _getTxWithDecodedMultiSigLogsAsync(txHash: string): Promise<TransactionReceiptWithDecodedLogs> {
-        const tx = await this._web3Wrapper.awaitTransactionMinedAsync(txHash, constants.AWAIT_TRANSACTION_MINED_MS);
-        tx.logs = _.filter(tx.logs, log => log.address === this._multiSig.address);
-        tx.logs = _.map(tx.logs, log => logDecoder.decodeLogOrThrow(log));
+        const tx = await this._logDecoder.getTxWithDecodedLogsAsync(txHash);
         return tx;
     }
 }
diff --git a/packages/contracts/src/utils/signing_utils.ts b/packages/contracts/src/utils/signing_utils.ts
index 41d63832e..d56d2cd44 100644
--- a/packages/contracts/src/utils/signing_utils.ts
+++ b/packages/contracts/src/utils/signing_utils.ts
@@ -7,19 +7,19 @@ export const signingUtils = {
             const prefixedMessage = ethUtil.hashPersonalMessage(message);
             const ecSignature = ethUtil.ecsign(prefixedMessage, privateKey);
             const signature = Buffer.concat([
-                ethUtil.toBuffer(signatureType),
                 ethUtil.toBuffer(ecSignature.v),
                 ecSignature.r,
                 ecSignature.s,
+                ethUtil.toBuffer(signatureType),
             ]);
             return signature;
         } else if (signatureType === SignatureType.EIP712) {
             const ecSignature = ethUtil.ecsign(message, privateKey);
             const signature = Buffer.concat([
-                ethUtil.toBuffer(signatureType),
                 ethUtil.toBuffer(ecSignature.v),
                 ecSignature.r,
                 ecSignature.s,
+                ethUtil.toBuffer(signatureType),
             ]);
             return signature;
         } else {
diff --git a/packages/contracts/src/utils/transaction_factory.ts b/packages/contracts/src/utils/transaction_factory.ts
index 41907132a..f66d55f9b 100644
--- a/packages/contracts/src/utils/transaction_factory.ts
+++ b/packages/contracts/src/utils/transaction_factory.ts
@@ -7,26 +7,25 @@ import { signingUtils } from './signing_utils';
 import { SignedTransaction } from './types';
 
 export class TransactionFactory {
-    private _signer: string;
+    private _signerBuff: Buffer;
     private _exchangeAddress: string;
     private _privateKey: Buffer;
     constructor(privateKey: Buffer, exchangeAddress: string) {
         this._privateKey = privateKey;
         this._exchangeAddress = exchangeAddress;
-        const signerBuff = ethUtil.privateToAddress(this._privateKey);
-        this._signer = `0x${signerBuff.toString('hex')}`;
+        this._signerBuff = ethUtil.privateToAddress(this._privateKey);
     }
     public newSignedTransaction(
         data: string,
         signatureType: SignatureType = SignatureType.Ecrecover,
     ): SignedTransaction {
         const salt = generatePseudoRandomSalt();
-        const txHash = crypto.solSHA3([this._exchangeAddress, salt, ethUtil.toBuffer(data)]);
+        const txHash = crypto.solSHA3([this._exchangeAddress, this._signerBuff, salt, ethUtil.toBuffer(data)]);
         const signature = signingUtils.signMessage(txHash, this._privateKey, signatureType);
         const signedTx = {
             exchangeAddress: this._exchangeAddress,
             salt,
-            signer: this._signer,
+            signer: `0x${this._signerBuff.toString('hex')}`,
             data,
             signature: `0x${signature.toString('hex')}`,
         };
diff --git a/packages/contracts/src/utils/types.ts b/packages/contracts/src/utils/types.ts
index 9a0c95504..a6c90dae0 100644
--- a/packages/contracts/src/utils/types.ts
+++ b/packages/contracts/src/utils/types.ts
@@ -105,6 +105,7 @@ export enum ContractName {
     DummyERC721Token = 'DummyERC721Token',
     TestLibBytes = 'TestLibBytes',
     Authorizable = 'Authorizable',
+    Whitelist = 'Whitelist',
 }
 
 export interface SignedTransaction {
diff --git a/packages/contracts/src/utils/web3_wrapper.ts b/packages/contracts/src/utils/web3_wrapper.ts
index 02595506b..4b8512222 100644
--- a/packages/contracts/src/utils/web3_wrapper.ts
+++ b/packages/contracts/src/utils/web3_wrapper.ts
@@ -7,7 +7,7 @@ import { coverage } from './coverage';
 
 export const txDefaults = {
     from: devConstants.TESTRPC_FIRST_ADDRESS,
-    gas: devConstants.GAS_ESTIMATE,
+    gas: devConstants.GAS_LIMIT,
 };
 const providerConfigs = { shouldUseInProcessGanache: true };
 export const provider = web3Factory.getRpcProvider(providerConfigs);