Update contracts with revert reasons and constructor keyword

41 files changed, 409 insertions, 180 deletions

diff --git a/packages/contracts/src/contracts/current/protocol/AssetProxy/IAssetProxy.sol b/packages/contracts/src/contracts/current/protocol/AssetProxy/IAssetProxy.sol
index df993a0ab..7675d684b 100644
--- a/packages/contracts/src/contracts/current/protocol/AssetProxy/IAssetProxy.sol
+++ b/packages/contracts/src/contracts/current/protocol/AssetProxy/IAssetProxy.sol
@@ -16,12 +16,14 @@
 
 */
 
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
 pragma experimental ABIEncoderV2;
 
 import "../../utils/Authorizable/IAuthorizable.sol";
 
-contract IAssetProxy is IAuthorizable {
+contract IAssetProxy is
+    IAuthorizable
+{
 
     /// @dev Transfers assets. Either succeeds or throws.
     /// @param assetMetadata Byte array encoded for the respective asset proxy.
diff --git a/packages/contracts/src/contracts/current/protocol/AssetProxy/MixinAssetProxy.sol b/packages/contracts/src/contracts/current/protocol/AssetProxy/MixinAssetProxy.sol
index 23dce6a8b..b96c84582 100644
--- a/packages/contracts/src/contracts/current/protocol/AssetProxy/MixinAssetProxy.sol
+++ b/packages/contracts/src/contracts/current/protocol/AssetProxy/MixinAssetProxy.sol
@@ -16,7 +16,7 @@
 
 */
 
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
 pragma experimental ABIEncoderV2;
 
 import "./mixins/MAssetProxy.sol";
@@ -25,8 +25,8 @@ import "../../utils/Authorizable/Authorizable.sol";
 
 contract MixinAssetProxy is 
     IAssetProxy,
-    MAssetProxy,
-    Authorizable
+    Authorizable,
+    MAssetProxy
 {
 
     /// @dev Transfers assets. Either succeeds or throws.
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 8e9b3bc65..d1276a61c 100644
--- a/packages/contracts/src/contracts/current/protocol/AssetProxy/mixins/MAssetProxy.sol
+++ b/packages/contracts/src/contracts/current/protocol/AssetProxy/mixins/MAssetProxy.sol
@@ -16,7 +16,7 @@
 
 */
 
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
 pragma experimental ABIEncoderV2;
 
 contract MAssetProxy {
diff --git a/packages/contracts/src/contracts/current/protocol/AssetProxy/proxies/ERC20Proxy.sol b/packages/contracts/src/contracts/current/protocol/AssetProxy/proxies/ERC20Proxy.sol
index 713e8a6e6..7e9b41f33 100644
--- a/packages/contracts/src/contracts/current/protocol/AssetProxy/proxies/ERC20Proxy.sol
+++ b/packages/contracts/src/contracts/current/protocol/AssetProxy/proxies/ERC20Proxy.sol
@@ -16,10 +16,9 @@
 
 */
 
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
 pragma experimental ABIEncoderV2;
 
-
 import "../../../utils/LibBytes/LibBytes.sol";
 import "../../../tokens/ERC20Token/IERC20Token.sol";
 import "../MixinAssetProxy.sol";
@@ -29,8 +28,14 @@ contract ERC20Proxy is
     MixinAssetProxy
 {
 
+    // Id of this proxy.
     uint8 constant PROXY_ID = 1;
 
+    // Revert reasons
+    string constant INVALID_METADATA_LENGTH = "Metadata must have a length of 21.";
+    string constant TRANSFER_FAILED = "Transfer failed.";
+    string constant PROXY_ID_MISMATCH = "Proxy id in metadata does not match this proxy id.";
+
     /// @dev Internal version of `transferFrom`.
     /// @param assetMetadata Encoded byte array.
     /// @param from Address to transfer asset from.
@@ -44,15 +49,24 @@ contract ERC20Proxy is
         internal
     {
         // Data must be intended for this proxy.
-        require(uint8(assetMetadata[0]) == PROXY_ID);
+        require(
+            uint8(assetMetadata[0]) == PROXY_ID,
+            PROXY_ID_MISMATCH
+        );
 
         // Decode metadata.
-        require(assetMetadata.length == 21);
+        require(
+            assetMetadata.length == 21,
+            INVALID_METADATA_LENGTH
+        );
         address token = readAddress(assetMetadata, 1);
 
         // Transfer tokens.
         bool success = IERC20Token(token).transferFrom(from, to, amount);
-        require(success == true);
+        require(
+            success == true,
+            TRANSFER_FAILED
+        );
     }
 
     /// @dev Gets the proxy id associated with the proxy address.
diff --git a/packages/contracts/src/contracts/current/protocol/AssetProxy/proxies/ERC721Proxy.sol b/packages/contracts/src/contracts/current/protocol/AssetProxy/proxies/ERC721Proxy.sol
index 6a4475d48..4d52893b0 100644
--- a/packages/contracts/src/contracts/current/protocol/AssetProxy/proxies/ERC721Proxy.sol
+++ b/packages/contracts/src/contracts/current/protocol/AssetProxy/proxies/ERC721Proxy.sol
@@ -16,7 +16,7 @@
 
 */
 
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
 pragma experimental ABIEncoderV2;
 
 import "../../../utils/LibBytes/LibBytes.sol";
@@ -28,8 +28,14 @@ contract ERC721Proxy is
     MixinAssetProxy
 {
 
+    // Id of this proxy.
     uint8 constant PROXY_ID = 2;
 
+    // Revert reasons
+    string constant INVALID_TRANSFER_AMOUNT = "Transfer amount must equal 1.";
+    string constant INVALID_METADATA_LENGTH = "Metadata must have a length of 53.";
+    string constant PROXY_ID_MISMATCH = "Proxy id in metadata does not match this proxy id.";
+
     /// @dev Internal version of `transferFrom`.
     /// @param assetMetadata Encoded byte array.
     /// @param from Address to transfer asset from.
@@ -43,13 +49,22 @@ contract ERC721Proxy is
         internal
     {
         // Data must be intended for this proxy.
-        require(uint8(assetMetadata[0]) == PROXY_ID);
+        require(
+            uint8(assetMetadata[0]) == PROXY_ID,
+            PROXY_ID_MISMATCH
+        );
 
         // There exists only 1 of each token.
-        require(amount == 1);
+        require(
+            amount == 1,
+            INVALID_TRANSFER_AMOUNT
+        );
 
-        // Decode metadata.
-        require(assetMetadata.length == 53);
+        // Decode metadata
+        require(
+            assetMetadata.length == 53,
+            INVALID_METADATA_LENGTH
+        );
         address token = readAddress(assetMetadata, 1);
         uint256 tokenId = readUint256(assetMetadata, 21);
 
diff --git a/packages/contracts/src/contracts/current/protocol/Exchange/Exchange.sol b/packages/contracts/src/contracts/current/protocol/Exchange/Exchange.sol
index e78446b99..85e2bc47e 100644
--- a/packages/contracts/src/contracts/current/protocol/Exchange/Exchange.sol
+++ b/packages/contracts/src/contracts/current/protocol/Exchange/Exchange.sol
@@ -16,7 +16,7 @@
 
 */
 
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
 pragma experimental ABIEncoderV2;
 
 import "./MixinExchangeCore.sol";
@@ -36,7 +36,7 @@ contract Exchange is
 {
     string constant public VERSION = "2.0.1-alpha";
 
-    function Exchange(bytes memory _zrxProxyData)
+    constructor (bytes memory _zrxProxyData)
         public
         MixinExchangeCore()
         MixinSignatureValidator()
diff --git a/packages/contracts/src/contracts/current/protocol/Exchange/ISigner.sol b/packages/contracts/src/contracts/current/protocol/Exchange/ISigner.sol
index d5641a09f..d604a1aec 100644
--- a/packages/contracts/src/contracts/current/protocol/Exchange/ISigner.sol
+++ b/packages/contracts/src/contracts/current/protocol/Exchange/ISigner.sol
@@ -16,7 +16,7 @@
 
 */
 
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
 pragma experimental ABIEncoderV2;
 
 contract ISigner {
diff --git a/packages/contracts/src/contracts/current/protocol/Exchange/LibErrors.sol b/packages/contracts/src/contracts/current/protocol/Exchange/LibErrors.sol
deleted file mode 100644
index 55160ad5b..000000000
--- a/packages/contracts/src/contracts/current/protocol/Exchange/LibErrors.sol
+++ /dev/null
@@ -1,35 +0,0 @@
-/*
-
-  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 ^0.4.21;
-pragma experimental ABIEncoderV2;
-
-contract LibErrors {
-
-    // Error Codes
-    enum Errors {
-        ORDER_EXPIRED,                    // Order has already expired
-        ORDER_FULLY_FILLED,               // Order has already been fully filled
-        ORDER_CANCELLED,                  // Order has already been cancelled
-        ROUNDING_ERROR_TOO_LARGE,         // Rounding error too large
-        INSUFFICIENT_BALANCE_OR_ALLOWANCE // Insufficient balance or allowance for token transfer
-    }
-
-    event ExchangeError(uint8 indexed errorId, bytes32 indexed orderHash);
-
-}
diff --git a/packages/contracts/src/contracts/current/protocol/Exchange/LibExchangeErrors.sol b/packages/contracts/src/contracts/current/protocol/Exchange/LibExchangeErrors.sol
new file mode 100644
index 000000000..cbd6cac29
--- /dev/null
+++ b/packages/contracts/src/contracts/current/protocol/Exchange/LibExchangeErrors.sol
@@ -0,0 +1,59 @@
+/*
+
+  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;
+
+contract LibExchangeErrors {
+
+    // Error Codes
+    enum Errors {
+        ORDER_EXPIRED,                     // Order has already expired
+        ORDER_FULLY_FILLED,                // Order has already been fully filled
+        ORDER_CANCELLED,                   // Order has already been cancelled
+        ROUNDING_ERROR_TOO_LARGE,          // Rounding error too large
+        INSUFFICIENT_BALANCE_OR_ALLOWANCE  // Insufficient balance or allowance for token transfer
+    }
+
+    event ExchangeError(uint8 indexed errorId, bytes32 indexed orderHash);
+
+    // Core revert reasons
+    string constant GREATER_THAN_ZERO_AMOUNT_REQUIRED = "Amount must be greater than 0.";
+    string constant SIGNATURE_VALIDATION_FAILED = "Signature validation failed.";
+    string constant INVALID_SENDER = "Invalid `msg.sender`.";
+    string constant INVALID_CONTEXT = "Function called in an invalid context.";
+    string constant INVALID_NEW_MAKER_EPOCH = "Specified salt must be greater than or equal to existing makerEpoch.";
+
+    // Transaction revert reasons
+    string constant DUPLICATE_TRANSACTION_HASH = "Transaction has already been executed.";
+    string constant TRANSACTION_EXECUTION_FAILED = "Transaction execution failed.";
+
+    // Wrapper revert reasons
+    string constant COMPLETE_FILL_FAILED = "Desired fill amount could not be completely filled.";
+    string constant ASSET_DATA_MISMATCH = "Asset data must be the same for each order.";
+
+    // Asset proxy dispatcher revert reasons
+    string constant GREATER_THAN_ZERO_LENGTH_REQUIRED = "Length must be greater than 0.";
+    string constant OLD_ASSET_PROXY_MISMATCH = "Old asset proxy does not match asset proxy at given id.";
+    string constant NEW_ASSET_PROXY_MISMATCH = "New asset proxy id does not match given id.";
+
+    // Signature validator revert reasons
+    string constant INVALID_SIGNATURE_LENGTH = "Invalid signature length.";
+    string constant ILLEGAL_SIGNATURE_TYPE = "Illegal signature type.";
+    string constant UNSUPPORTED_SIGNATURE_TYPE = "Unsupported signature type.";
+}
diff --git a/packages/contracts/src/contracts/current/protocol/Exchange/LibFillResults.sol b/packages/contracts/src/contracts/current/protocol/Exchange/LibFillResults.sol
index 41096f448..e26da2bce 100644
--- a/packages/contracts/src/contracts/current/protocol/Exchange/LibFillResults.sol
+++ b/packages/contracts/src/contracts/current/protocol/Exchange/LibFillResults.sol
@@ -16,12 +16,14 @@
 
 */
 
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
 pragma experimental ABIEncoderV2;
 
 import "../../utils/SafeMath/SafeMath.sol";
 
-contract LibFillResults is SafeMath {
+contract LibFillResults is
+    SafeMath
+{
 
     struct FillResults {
         uint256 makerAssetFilledAmount;
diff --git a/packages/contracts/src/contracts/current/protocol/Exchange/LibMath.sol b/packages/contracts/src/contracts/current/protocol/Exchange/LibMath.sol
index 3b553ebbc..761c300a1 100644
--- a/packages/contracts/src/contracts/current/protocol/Exchange/LibMath.sol
+++ b/packages/contracts/src/contracts/current/protocol/Exchange/LibMath.sol
@@ -16,12 +16,14 @@
 
 */
 
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
 pragma experimental ABIEncoderV2;
 
 import "../../utils/SafeMath/SafeMath.sol";
 
-contract LibMath is SafeMath {
+contract LibMath is
+    SafeMath
+{
 
     /// @dev Calculates partial value given a numerator and denominator.
     /// @param numerator Numerator.
diff --git a/packages/contracts/src/contracts/current/protocol/Exchange/LibOrder.sol b/packages/contracts/src/contracts/current/protocol/Exchange/LibOrder.sol
index df974e177..32554f45b 100644
--- a/packages/contracts/src/contracts/current/protocol/Exchange/LibOrder.sol
+++ b/packages/contracts/src/contracts/current/protocol/Exchange/LibOrder.sol
@@ -16,7 +16,7 @@
 
 */
 
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
 pragma experimental ABIEncoderV2;
 
 contract LibOrder {
diff --git a/packages/contracts/src/contracts/current/protocol/Exchange/MixinAssetProxyDispatcher.sol b/packages/contracts/src/contracts/current/protocol/Exchange/MixinAssetProxyDispatcher.sol
index b73c6ca90..eb423ad28 100644
--- a/packages/contracts/src/contracts/current/protocol/Exchange/MixinAssetProxyDispatcher.sol
+++ b/packages/contracts/src/contracts/current/protocol/Exchange/MixinAssetProxyDispatcher.sol
@@ -16,13 +16,16 @@
 
 */
 
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
+pragma experimental ABIEncoderV2;
 
 import "../../utils/Ownable/Ownable.sol";
 import "../AssetProxy/IAssetProxy.sol";
+import "./LibExchangeErrors.sol";
 import "./mixins/MAssetProxyDispatcher.sol";
 
 contract MixinAssetProxyDispatcher is
+    LibExchangeErrors,
     Ownable,
     MAssetProxyDispatcher
 {
@@ -43,8 +46,11 @@ contract MixinAssetProxyDispatcher is
     {
         // Do nothing if no amount should be transferred.
         if (amount > 0) {
-            // Lookup asset proxy.
-            require(assetMetadata.length >= 1);
+            // Lookup asset proxy
+            require(
+                assetMetadata.length >= 1,
+                GREATER_THAN_ZERO_LENGTH_REQUIRED
+            );
             uint8 assetProxyId = uint8(assetMetadata[0]);
             IAssetProxy assetProxy = assetProxies[assetProxyId];
 
@@ -65,15 +71,21 @@ contract MixinAssetProxyDispatcher is
         external
         onlyOwner
     {
-        // Ensure the existing asset proxy is not unintentionally overwritten.
-        require(oldAssetProxy == address(assetProxies[assetProxyId]));
+        // Ensure the existing asset proxy is not unintentionally overwritten
+        require(
+            oldAssetProxy == address(assetProxies[assetProxyId]),
+            OLD_ASSET_PROXY_MISMATCH
+        );
 
         IAssetProxy assetProxy = IAssetProxy(newAssetProxy);
 
         // Ensure that the id of newAssetProxy matches the passed in assetProxyId, unless it is being reset to 0.
         if (newAssetProxy != address(0)) {
             uint8 newAssetProxyId = assetProxy.getProxyId();
-            require(newAssetProxyId == assetProxyId);
+            require(
+                newAssetProxyId == assetProxyId,
+                NEW_ASSET_PROXY_MISMATCH
+            );
         }
 
         // Add asset proxy and log registration.
@@ -89,7 +101,7 @@ contract MixinAssetProxyDispatcher is
         view
         returns (address)
     {
-        IAssetProxy assetProxy = assetProxies[assetProxyId];
-        return address(assetProxy);
+        address assetProxy = address(assetProxies[assetProxyId]);
+        return assetProxy;
     }
 }
diff --git a/packages/contracts/src/contracts/current/protocol/Exchange/MixinExchangeCore.sol b/packages/contracts/src/contracts/current/protocol/Exchange/MixinExchangeCore.sol
index 4ca271b2a..d764d7a4f 100644
--- a/packages/contracts/src/contracts/current/protocol/Exchange/MixinExchangeCore.sol
+++ b/packages/contracts/src/contracts/current/protocol/Exchange/MixinExchangeCore.sol
@@ -16,13 +16,13 @@
 
 */
 
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
 pragma experimental ABIEncoderV2;
 
 import "./LibFillResults.sol";
 import "./LibOrder.sol";
-import "./LibErrors.sol";
 import "./LibMath.sol";
+import "./LibExchangeErrors.sol";
 import "./mixins/MExchangeCore.sol";
 import "./mixins/MSettlement.sol";
 import "./mixins/MSignatureValidator.sol";
@@ -34,8 +34,8 @@ import "./mixins/MTransactions.sol";
 contract MixinExchangeCore is
     LibOrder,
     LibFillResults,
-    LibErrors,
     LibMath,
+    LibExchangeErrors,
     MExchangeCore,
     MSettlement,
     MSignatureValidator,
@@ -111,22 +111,40 @@ contract MixinExchangeCore is
         // Validate order and maker only if first time seen
         // TODO: Read filled and cancelled only once
         if (filled[orderHash] == 0) {
-            require(order.makerAssetAmount > 0);
-            require(order.takerAssetAmount > 0);
-            require(isValidSignature(orderHash, order.makerAddress, signature));
+            require(
+                order.makerAssetAmount > 0,
+                GREATER_THAN_ZERO_AMOUNT_REQUIRED
+            );
+            require(
+                order.takerAssetAmount > 0,
+                GREATER_THAN_ZERO_AMOUNT_REQUIRED
+            );
+            require(
+                isValidSignature(orderHash, order.makerAddress, signature),
+                SIGNATURE_VALIDATION_FAILED
+            );
         }
         
         // Validate sender is allowed to fill this order
         if (order.senderAddress != address(0)) {
-            require(order.senderAddress == msg.sender);
+            require(
+                order.senderAddress == msg.sender,
+                INVALID_SENDER
+            );
         }
 
         // Validate taker is allowed to fill this order
         address takerAddress = getCurrentContextAddress();
         if (order.takerAddress != address(0)) {
-            require(order.takerAddress == takerAddress);
+            require(
+                order.takerAddress == takerAddress,
+                INVALID_CONTEXT
+            );
         }
-        require(takerAssetFillAmount > 0);
+        require(
+            takerAssetFillAmount > 0,
+            GREATER_THAN_ZERO_AMOUNT_REQUIRED
+        );
 
         // Validate order expiration
         if (block.timestamp >= order.expirationTimeSeconds) {
@@ -173,17 +191,29 @@ contract MixinExchangeCore is
         bytes32 orderHash = getOrderHash(order);
 
         // Validate the order
-        require(order.makerAssetAmount > 0);
-        require(order.takerAssetAmount > 0);
+        require(
+            order.makerAssetAmount > 0,
+            GREATER_THAN_ZERO_AMOUNT_REQUIRED
+        );
+        require(
+            order.takerAssetAmount > 0,
+            GREATER_THAN_ZERO_AMOUNT_REQUIRED
+        );
 
         // Validate sender is allowed to cancel this order
         if (order.senderAddress != address(0)) {
-            require(order.senderAddress == msg.sender);
+            require(
+                order.senderAddress == msg.sender,
+                INVALID_SENDER
+            );
         }
         
         // Validate transaction signed by maker
         address makerAddress = getCurrentContextAddress();
-        require(order.makerAddress == makerAddress);
+        require(
+            order.makerAddress == makerAddress,
+            INVALID_CONTEXT
+        );
         
         if (block.timestamp >= order.expirationTimeSeconds) {
             emit ExchangeError(uint8(Errors.ORDER_EXPIRED), orderHash);
@@ -211,8 +241,11 @@ contract MixinExchangeCore is
     function cancelOrdersUpTo(uint256 salt)
         external
     {
-        uint256 newMakerEpoch = salt + 1;                // makerEpoch is initialized to 0, so to cancelUpTo we need salt+1
-        require(newMakerEpoch > makerEpoch[msg.sender]); // epoch must be monotonically increasing
+        uint256 newMakerEpoch = salt + 1;  // makerEpoch is initialized to 0, so to cancelUpTo we need salt + 1
+        require(
+            newMakerEpoch > makerEpoch[msg.sender],  // epoch must be monotonically increasing
+            INVALID_NEW_MAKER_EPOCH
+        );
         makerEpoch[msg.sender] = newMakerEpoch;
         emit CancelUpTo(msg.sender, newMakerEpoch);
     }
diff --git a/packages/contracts/src/contracts/current/protocol/Exchange/MixinSettlement.sol b/packages/contracts/src/contracts/current/protocol/Exchange/MixinSettlement.sol
index cab2ccfb6..3e805aa8e 100644
--- a/packages/contracts/src/contracts/current/protocol/Exchange/MixinSettlement.sol
+++ b/packages/contracts/src/contracts/current/protocol/Exchange/MixinSettlement.sol
@@ -16,7 +16,7 @@
 
 */
 
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
 pragma experimental ABIEncoderV2;
 
 import "./mixins/MSettlement.sol";
@@ -41,7 +41,7 @@ contract MixinSettlement is
         return ZRX_PROXY_DATA;
     }
 
-    function MixinSettlement(bytes memory _zrxProxyData)
+    constructor (bytes memory _zrxProxyData)
         public
     {
         ZRX_PROXY_DATA = _zrxProxyData;
diff --git a/packages/contracts/src/contracts/current/protocol/Exchange/MixinSignatureValidator.sol b/packages/contracts/src/contracts/current/protocol/Exchange/MixinSignatureValidator.sol
index 690a70820..3091adcaf 100644
--- a/packages/contracts/src/contracts/current/protocol/Exchange/MixinSignatureValidator.sol
+++ b/packages/contracts/src/contracts/current/protocol/Exchange/MixinSignatureValidator.sol
@@ -16,15 +16,20 @@
 
 */
 
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
 pragma experimental ABIEncoderV2;
 
 import "./mixins/MSignatureValidator.sol";
 import "./ISigner.sol";
+import "./LibExchangeErrors.sol";
+import "../../utils/LibBytes/LibBytes.sol";
 
 /// @dev Provides MSignatureValidator
-contract MixinSignatureValidator is MSignatureValidator {
-
+contract MixinSignatureValidator is
+    LibBytes,
+    LibExchangeErrors,
+    MSignatureValidator
+{
     enum SignatureType {
         Illegal, // Default value
         Invalid,
@@ -54,7 +59,10 @@ contract MixinSignatureValidator is MSignatureValidator {
     {
         // TODO: Domain separation: make hash depend on role. (Taker sig should not be valid as maker sig, etc.)
 
-        require(signature.length >= 1);
+        require(
+            signature.length >= 1,
+            INVALID_SIGNATURE_LENGTH
+        );
         SignatureType signatureType = SignatureType(uint8(signature[0]));
 
         // Variables are not scoped in Solidity
@@ -69,14 +77,18 @@ contract MixinSignatureValidator is MSignatureValidator {
         // it an explicit option. This aids testing and analysis. It is
         // also the initialization value for the enum type.
         if (signatureType == SignatureType.Illegal) {
-            revert();
+            // NOTE: Reason cannot be assigned to a variable because of https://github.com/ethereum/solidity/issues/4051
+            revert("Illegal signature type.");
 
         // 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);
+            require(
+                signature.length == 1,
+                INVALID_SIGNATURE_LENGTH
+            );
             isValid = false;
             return isValid;
 
@@ -89,16 +101,22 @@ contract MixinSignatureValidator is MSignatureValidator {
         // `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 == 1);
+            require(
+                signature.length == 1,
+                INVALID_SIGNATURE_LENGTH
+            );
             isValid = signer == msg.sender;
             return isValid;
 
         // Signed using web3.eth_sign
         } else if (signatureType == SignatureType.Ecrecover) {
-            require(signature.length == 66);
+            require(
+                signature.length == 66,
+                INVALID_SIGNATURE_LENGTH
+            );
             v = uint8(signature[1]);
-            r = get32(signature, 2);
-            s = get32(signature, 34);
+            r = readBytes32(signature, 2);
+            s = readBytes32(signature, 34);
             recovered = ecrecover(
                 keccak256("\x19Ethereum Signed Message:\n32", hash),
                 v,
@@ -110,10 +128,13 @@ contract MixinSignatureValidator is MSignatureValidator {
 
         // Signature using EIP712
         } else if (signatureType == SignatureType.EIP712) {
-            require(signature.length == 66);
+            require(
+                signature.length == 66,
+                INVALID_SIGNATURE_LENGTH
+            );
             v = uint8(signature[1]);
-            r = get32(signature, 2);
-            s = get32(signature, 34);
+            r = readBytes32(signature, 2);
+            s = readBytes32(signature, 34);
             recovered = ecrecover(hash, v, r, s);
             isValid = signer == recovered;
             return isValid;
@@ -127,10 +148,13 @@ contract MixinSignatureValidator is MSignatureValidator {
         // https://github.com/trezor/trezor-mcu/blob/master/firmware/ethereum.c#L602
         // https://github.com/trezor/trezor-mcu/blob/master/firmware/crypto.c#L36
         } else if (signatureType == SignatureType.Trezor) {
-            require(signature.length == 66);
+            require(
+                signature.length == 66,
+                INVALID_SIGNATURE_LENGTH
+            );
             v = uint8(signature[1]);
-            r = get32(signature, 2);
-            s = get32(signature, 34);
+            r = readBytes32(signature, 2);
+            s = readBytes32(signature, 34);
             recovered = ecrecover(
                 keccak256("\x19Ethereum Signed Message:\n\x41", hash),
                 v,
@@ -156,7 +180,8 @@ contract MixinSignatureValidator is MSignatureValidator {
         // that we currently support. In this case returning false
         // may lead the caller to incorrectly believe that the
         // signature was invalid.)
-        revert();
+        // NOTE: Reason cannot be assigned to a variable because of https://github.com/ethereum/solidity/issues/4051
+        revert("Unsupported signature type.");
     }
 
     /// @dev Approves a hash on-chain using any valid signature type.
@@ -169,24 +194,10 @@ contract MixinSignatureValidator is MSignatureValidator {
         bytes signature)
         external
     {
-        require(isValidSignature(hash, signer, signature));
+        require(
+            isValidSignature(hash, signer, signature),
+            SIGNATURE_VALIDATION_FAILED
+        );
         preSigned[hash][signer] = true;
     }
-
-    function get32(bytes memory b, uint256 index)
-        private pure
-        returns (bytes32 result)
-    {
-        require(b.length >= index + 32);
-
-        // Arrays are prefixed by a 256 bit length parameter
-        index += 32;
-
-        // Read the bytes32 from array memory
-        assembly {
-            result := mload(add(b, index))
-        }
-        return result;
-    }
-
 }
diff --git a/packages/contracts/src/contracts/current/protocol/Exchange/MixinTransactions.sol b/packages/contracts/src/contracts/current/protocol/Exchange/MixinTransactions.sol
index 9edb1694f..670d454d6 100644
--- a/packages/contracts/src/contracts/current/protocol/Exchange/MixinTransactions.sol
+++ b/packages/contracts/src/contracts/current/protocol/Exchange/MixinTransactions.sol
@@ -20,8 +20,10 @@ pragma experimental ABIEncoderV2;
 
 import "./mixins/MSignatureValidator.sol";
 import "./mixins/MTransactions.sol";
+import "./LibExchangeErrors.sol";
 
 contract MixinTransactions is
+    LibExchangeErrors,
     MSignatureValidator,
     MTransactions
 {
@@ -56,12 +58,18 @@ contract MixinTransactions is
         );
 
         // Validate transaction has not been executed
-        require(!transactions[transactionHash]);
+        require(
+            !transactions[transactionHash],
+            DUPLICATE_TRANSACTION_HASH
+        );
 
         // TODO: is SignatureType.Caller necessary if we make this check?
         if (signer != msg.sender) {
             // Validate signature
-            require(isValidSignature(transactionHash, signer, signature));
+            require(
+                isValidSignature(transactionHash, signer, signature),
+                SIGNATURE_VALIDATION_FAILED
+            );
 
             // Set the current transaction signer
             currentContextAddress = signer;
@@ -69,7 +77,10 @@ contract MixinTransactions is
 
         // Execute transaction
         transactions[transactionHash] = true;
-        require(address(this).delegatecall(data));
+        require(
+            address(this).delegatecall(data),
+            TRANSACTION_EXECUTION_FAILED
+        );
 
         // Reset current transaction signer
         // TODO: Check if gas is paid when currentContextAddress is already 0.
diff --git a/packages/contracts/src/contracts/current/protocol/Exchange/MixinWrapperFunctions.sol b/packages/contracts/src/contracts/current/protocol/Exchange/MixinWrapperFunctions.sol
index 105c0f0a0..0cfcf0c25 100644
--- a/packages/contracts/src/contracts/current/protocol/Exchange/MixinWrapperFunctions.sol
+++ b/packages/contracts/src/contracts/current/protocol/Exchange/MixinWrapperFunctions.sol
@@ -16,7 +16,7 @@
 
 */
 
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
 pragma experimental ABIEncoderV2;
 
 import "../../utils/LibBytes/LibBytes.sol";
@@ -24,6 +24,7 @@ import "./mixins/MExchangeCore.sol";
 import "./LibMath.sol";
 import "./LibOrder.sol";
 import "./LibFillResults.sol";
+import "./LibExchangeErrors.sol";
 
 /// @dev Consumes MExchangeCore
 contract MixinWrapperFunctions is
@@ -31,6 +32,7 @@ contract MixinWrapperFunctions is
     LibFillResults,
     LibMath,
     LibBytes,
+    LibExchangeErrors,
     MExchangeCore
 {
     /// @dev Fills the input order. Reverts if exact takerAssetFillAmount not filled.
@@ -49,7 +51,10 @@ contract MixinWrapperFunctions is
             takerAssetFillAmount,
             signature
         );
-        require(fillResults.takerAssetFilledAmount == takerAssetFillAmount);
+        require(
+            fillResults.takerAssetFilledAmount == takerAssetFillAmount,
+            COMPLETE_FILL_FAILED
+        );
         return fillResults;
     }
 
@@ -327,7 +332,11 @@ contract MixinWrapperFunctions is
         for (uint256 i = 0; i < orders.length; i++) {
 
             // Token being sold by taker must be the same for each order
-            require(areBytesEqual(orders[i].takerAssetData, orders[0].takerAssetData));
+            // TODO: optimize by only using takerAssetData for first order.
+            require(
+                areBytesEqual(orders[i].takerAssetData, orders[0].takerAssetData),
+                ASSET_DATA_MISMATCH
+            );
 
             // Calculate the remaining amount of takerAsset to sell
             uint256 remainingTakerAssetFillAmount = safeSub(takerAssetFillAmount, totalFillResults.takerAssetFilledAmount);
@@ -366,7 +375,11 @@ contract MixinWrapperFunctions is
         for (uint256 i = 0; i < orders.length; i++) {
 
             // Token being sold by taker must be the same for each order
-            require(areBytesEqual(orders[i].takerAssetData, orders[0].takerAssetData));
+            // TODO: optimize by only using takerAssetData for first order.
+            require(
+                areBytesEqual(orders[i].takerAssetData, orders[0].takerAssetData),
+                ASSET_DATA_MISMATCH
+            );
 
             // Calculate the remaining amount of takerAsset to sell
             uint256 remainingTakerAssetFillAmount = safeSub(takerAssetFillAmount, totalFillResults.takerAssetFilledAmount);
@@ -404,7 +417,11 @@ contract MixinWrapperFunctions is
         for (uint256 i = 0; i < orders.length; i++) {
 
             // Token being bought by taker must be the same for each order
-            require(areBytesEqual(orders[i].makerAssetData, orders[0].makerAssetData));
+            // TODO: optimize by only using makerAssetData for first order.
+            require(
+                areBytesEqual(orders[i].makerAssetData, orders[0].makerAssetData),
+                ASSET_DATA_MISMATCH
+            );
 
             // Calculate the remaining amount of makerAsset to buy
             uint256 remainingMakerAssetFillAmount = safeSub(makerAssetFillAmount, totalFillResults.makerAssetFilledAmount);
@@ -451,7 +468,11 @@ contract MixinWrapperFunctions is
         for (uint256 i = 0; i < orders.length; i++) {
 
             // Token being bought by taker must be the same for each order
-            require(areBytesEqual(orders[i].makerAssetData, orders[0].makerAssetData));
+            // TODO: optimize by only using makerAssetData for first order.
+            require(
+                areBytesEqual(orders[i].makerAssetData, orders[0].makerAssetData),
+                ASSET_DATA_MISMATCH
+            );
 
             // Calculate the remaining amount of makerAsset to buy
             uint256 remainingMakerAssetFillAmount = safeSub(makerAssetFillAmount, totalFillResults.makerAssetFilledAmount);
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 0cf750d7d..df2250cd9 100644
--- a/packages/contracts/src/contracts/current/protocol/Exchange/mixins/MAssetProxyDispatcher.sol
+++ b/packages/contracts/src/contracts/current/protocol/Exchange/mixins/MAssetProxyDispatcher.sol
@@ -16,7 +16,8 @@
 
 */
 
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
+pragma experimental ABIEncoderV2;
 
 contract MAssetProxyDispatcher {
 
diff --git a/packages/contracts/src/contracts/current/protocol/Exchange/mixins/MExchangeCore.sol b/packages/contracts/src/contracts/current/protocol/Exchange/mixins/MExchangeCore.sol
index 656df079e..6bd8fd9b6 100644
--- a/packages/contracts/src/contracts/current/protocol/Exchange/mixins/MExchangeCore.sol
+++ b/packages/contracts/src/contracts/current/protocol/Exchange/mixins/MExchangeCore.sol
@@ -16,7 +16,7 @@
 
 */
 
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
 pragma experimental ABIEncoderV2;
 
 import "../LibOrder.sol";
diff --git a/packages/contracts/src/contracts/current/protocol/Exchange/mixins/MSettlement.sol b/packages/contracts/src/contracts/current/protocol/Exchange/mixins/MSettlement.sol
index 0d7e59a9a..9cb2afeb0 100644
--- a/packages/contracts/src/contracts/current/protocol/Exchange/mixins/MSettlement.sol
+++ b/packages/contracts/src/contracts/current/protocol/Exchange/mixins/MSettlement.sol
@@ -16,7 +16,7 @@
 
 */
 
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
 pragma experimental ABIEncoderV2;
 
 import "../LibOrder.sol";
@@ -33,5 +33,5 @@ contract MSettlement {
             uint256 makerFeePaid,
             uint256 takerFeePaid
         );
-
 }
+
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 043a7da9c..2b8ae78dd 100644
--- a/packages/contracts/src/contracts/current/protocol/Exchange/mixins/MSignatureValidator.sol
+++ b/packages/contracts/src/contracts/current/protocol/Exchange/mixins/MSignatureValidator.sol
@@ -16,7 +16,7 @@
 
 */
 
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
 pragma experimental ABIEncoderV2;
 
 contract MSignatureValidator {
diff --git a/packages/contracts/src/contracts/current/protocol/Exchange/mixins/MTransactions.sol b/packages/contracts/src/contracts/current/protocol/Exchange/mixins/MTransactions.sol
index 10bfcb035..3d167c0bc 100644
--- a/packages/contracts/src/contracts/current/protocol/Exchange/mixins/MTransactions.sol
+++ b/packages/contracts/src/contracts/current/protocol/Exchange/mixins/MTransactions.sol
@@ -15,12 +15,10 @@
   limitations under the License.
 
 */
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
 pragma experimental ABIEncoderV2;
 
-import "./MSignatureValidator.sol";
-
-contract MTransactions is MSignatureValidator {
+contract MTransactions {
 
     /// @dev Executes an exchange method call in the context of signer.
     /// @param salt Arbitrary number to ensure uniqueness of transaction hash.
diff --git a/packages/contracts/src/contracts/current/test/DummyERC20Token/DummyERC20Token.sol b/packages/contracts/src/contracts/current/test/DummyERC20Token/DummyERC20Token.sol
index 2626399c2..ab5311e0c 100644
--- a/packages/contracts/src/contracts/current/test/DummyERC20Token/DummyERC20Token.sol
+++ b/packages/contracts/src/contracts/current/test/DummyERC20Token/DummyERC20Token.sol
@@ -16,7 +16,8 @@
 
 */
 
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
+pragma experimental ABIEncoderV2;
 
 import "../Mintable/Mintable.sol";
 import "../../utils/Ownable/Ownable.sol";
@@ -26,7 +27,7 @@ contract DummyERC20Token is Mintable, Ownable {
     string public symbol;
     uint256 public decimals;
 
-    function DummyERC20Token(
+    constructor (
         string _name,
         string _symbol,
         uint256 _decimals,
diff --git a/packages/contracts/src/contracts/current/test/DummyERC721Token/DummyERC721Token.sol b/packages/contracts/src/contracts/current/test/DummyERC721Token/DummyERC721Token.sol
index 4fbaa6b74..22ebbd3c1 100644
--- a/packages/contracts/src/contracts/current/test/DummyERC721Token/DummyERC721Token.sol
+++ b/packages/contracts/src/contracts/current/test/DummyERC721Token/DummyERC721Token.sol
@@ -16,7 +16,9 @@
 
 */
 
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
+pragma experimental ABIEncoderV2;
+
 import "../../tokens/ERC721Token/ERC721Token.sol";
 import "../../utils/Ownable/Ownable.sol";
 
@@ -30,7 +32,7 @@ contract DummyERC721Token is
     * @param name of token
     * @param symbol of token
     */
-    function DummyERC721Token(
+    constructor (
         string name,
         string symbol)
         public
@@ -47,7 +49,10 @@ contract DummyERC721Token is
         public
         onlyOwner
     {
-        require(!exists(tokenId));
+        require(
+            !exists(tokenId),
+            "Token with tokenId already exists."
+        );
         _mint(to, tokenId);
     }
 }
diff --git a/packages/contracts/src/contracts/current/test/Mintable/Mintable.sol b/packages/contracts/src/contracts/current/test/Mintable/Mintable.sol
index 305737b72..fd944f244 100644
--- a/packages/contracts/src/contracts/current/test/Mintable/Mintable.sol
+++ b/packages/contracts/src/contracts/current/test/Mintable/Mintable.sol
@@ -16,7 +16,8 @@
 
 */
 
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
+pragma experimental ABIEncoderV2;
 
 import "../../tokens/UnlimitedAllowanceToken/UnlimitedAllowanceToken.sol";
 import "../../utils/SafeMath/SafeMath.sol";
@@ -29,7 +30,10 @@ contract Mintable is UnlimitedAllowanceToken, SafeMath {
     function mint(uint256 _value)
         public
     {
-        require(_value <= 100000000000000000000);
+        require(
+            _value <= 100000000000000000000,
+            "Minting more than 100000000000000000000 is not allowed."
+        );
         balances[msg.sender] = safeAdd(_value, balances[msg.sender]);
         totalSupply = safeAdd(totalSupply, _value);
     }
diff --git a/packages/contracts/src/contracts/current/test/TestAssetProxyDispatcher/TestAssetProxyDispatcher.sol b/packages/contracts/src/contracts/current/test/TestAssetProxyDispatcher/TestAssetProxyDispatcher.sol
index 8206b84bd..93ec3cef3 100644
--- a/packages/contracts/src/contracts/current/test/TestAssetProxyDispatcher/TestAssetProxyDispatcher.sol
+++ b/packages/contracts/src/contracts/current/test/TestAssetProxyDispatcher/TestAssetProxyDispatcher.sol
@@ -16,7 +16,8 @@
 
 */
 
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
+pragma experimental ABIEncoderV2;
 
 import "../../protocol/Exchange/MixinAssetProxyDispatcher.sol";
 
diff --git a/packages/contracts/src/contracts/current/test/TestLibs/TestLibs.sol b/packages/contracts/src/contracts/current/test/TestLibs/TestLibs.sol
index a5b327a90..5a16ae947 100644
--- a/packages/contracts/src/contracts/current/test/TestLibs/TestLibs.sol
+++ b/packages/contracts/src/contracts/current/test/TestLibs/TestLibs.sol
@@ -16,7 +16,7 @@
 
 */
 
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
 pragma experimental ABIEncoderV2;
 
 import "../../protocol/Exchange/LibMath.sol";
diff --git a/packages/contracts/src/contracts/current/test/TestSignatureValidator/TestSignatureValidator.sol b/packages/contracts/src/contracts/current/test/TestSignatureValidator/TestSignatureValidator.sol
index 4ba04b64e..20202cd7b 100644
--- a/packages/contracts/src/contracts/current/test/TestSignatureValidator/TestSignatureValidator.sol
+++ b/packages/contracts/src/contracts/current/test/TestSignatureValidator/TestSignatureValidator.sol
@@ -16,7 +16,7 @@
 
 */
 
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
 pragma experimental ABIEncoderV2;
 
 import "../../protocol/Exchange/MixinSignatureValidator.sol";
diff --git a/packages/contracts/src/contracts/current/tokens/ERC20Token/ERC20Token.sol b/packages/contracts/src/contracts/current/tokens/ERC20Token/ERC20Token.sol
index 13ceeb2c6..27e7fa355 100644
--- a/packages/contracts/src/contracts/current/tokens/ERC20Token/ERC20Token.sol
+++ b/packages/contracts/src/contracts/current/tokens/ERC20Token/ERC20Token.sol
@@ -16,7 +16,8 @@
 
 */
 
-pragma solidity ^0.4.18;
+pragma solidity ^0.4.23;
+pragma experimental ABIEncoderV2;
 
 import "./IERC20Token.sol";
 
@@ -26,7 +27,14 @@ contract ERC20Token is IERC20Token {
         public
         returns (bool)
     {
-        require(balances[msg.sender] >= _value && balances[_to] + _value >= balances[_to]);
+        require(
+            balances[msg.sender] >= _value,
+            "Insufficient balance to complete transfer."
+        );
+        require(
+            balances[_to] + _value >= balances[_to],
+            "Transfer would result in an overflow."
+        );
         balances[msg.sender] -= _value;
         balances[_to] += _value;
         emit Transfer(msg.sender, _to, _value);
@@ -37,7 +45,18 @@ contract ERC20Token is IERC20Token {
         public
         returns (bool)
     {
-        require(balances[_from] >= _value && allowed[_from][msg.sender] >= _value && balances[_to] + _value >= balances[_to]);
+        require(
+            balances[_from] >= _value,
+            "Insufficient balance to complete transfer."
+        );
+        require(
+            allowed[_from][msg.sender] >= _value,
+            "Insufficient allowance to complete transfer."
+        );
+        require(
+            balances[_to] + _value >= balances[_to],
+            "Transfer would result in an overflow."
+        );
         balances[_to] += _value;
         balances[_from] -= _value;
         allowed[_from][msg.sender] -= _value;
diff --git a/packages/contracts/src/contracts/current/tokens/ERC20Token/IERC20Token.sol b/packages/contracts/src/contracts/current/tokens/ERC20Token/IERC20Token.sol
index 0159b31e8..537f5a83d 100644
--- a/packages/contracts/src/contracts/current/tokens/ERC20Token/IERC20Token.sol
+++ b/packages/contracts/src/contracts/current/tokens/ERC20Token/IERC20Token.sol
@@ -16,11 +16,12 @@
 
 */
 
-pragma solidity ^0.4.18;
+pragma solidity ^0.4.23;
+pragma experimental ABIEncoderV2;
 
 contract IERC20Token {
 
-    /// @notice send `_value` token to `_to` from `msg.sender`
+    /// @notice send `value` token to `to` from `msg.sender`
     /// @param _to The address of the recipient
     /// @param _value The amount of token to be transferred
     /// @return Whether the transfer was successful or not
@@ -28,7 +29,7 @@ contract IERC20Token {
         public
         returns (bool);
 
-    /// @notice send `_value` token to `_to` from `_from` on the condition it is approved by `_from`
+    /// @notice send `value` token to `to` from `from` on the condition it is approved by `from`
     /// @param _from The address of the sender
     /// @param _to The address of the recipient
     /// @param _value The amount of token to be transferred
@@ -61,10 +62,12 @@ contract IERC20Token {
     event Transfer(
         address indexed _from,
         address indexed _to,
-        uint256 _value);
+        uint256 _value
+    );
     
     event Approval(
         address indexed _owner,
         address indexed _spender,
-        uint256 _value);
+        uint256 _value
+    );
 }
diff --git a/packages/contracts/src/contracts/current/tokens/ERC721Token/ERC721Token.sol b/packages/contracts/src/contracts/current/tokens/ERC721Token/ERC721Token.sol
index 3bf064c3f..b3493bc99 100644
--- a/packages/contracts/src/contracts/current/tokens/ERC721Token/ERC721Token.sol
+++ b/packages/contracts/src/contracts/current/tokens/ERC721Token/ERC721Token.sol
@@ -23,7 +23,7 @@ TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */
 
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
 
 import "./IERC721Token.sol";
 import "./IERC721Receiver.sol";
diff --git a/packages/contracts/src/contracts/current/tokens/ERC721Token/IERC721Receiver.sol b/packages/contracts/src/contracts/current/tokens/ERC721Token/IERC721Receiver.sol
index 26871cc89..3484bf824 100644
--- a/packages/contracts/src/contracts/current/tokens/ERC721Token/IERC721Receiver.sol
+++ b/packages/contracts/src/contracts/current/tokens/ERC721Token/IERC721Receiver.sol
@@ -23,7 +23,7 @@ TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */
 
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
 
 /**
  * @title ERC721 token receiver interface
diff --git a/packages/contracts/src/contracts/current/tokens/ERC721Token/IERC721Token.sol b/packages/contracts/src/contracts/current/tokens/ERC721Token/IERC721Token.sol
index 73741ed53..81e1b97af 100644
--- a/packages/contracts/src/contracts/current/tokens/ERC721Token/IERC721Token.sol
+++ b/packages/contracts/src/contracts/current/tokens/ERC721Token/IERC721Token.sol
@@ -23,7 +23,7 @@ TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */
 
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
 
 /**
  * @title ERC721 Non-Fungible Token Standard basic interface
diff --git a/packages/contracts/src/contracts/current/tokens/UnlimitedAllowanceToken/UnlimitedAllowanceToken.sol b/packages/contracts/src/contracts/current/tokens/UnlimitedAllowanceToken/UnlimitedAllowanceToken.sol
index be774e374..4aedced49 100644
--- a/packages/contracts/src/contracts/current/tokens/UnlimitedAllowanceToken/UnlimitedAllowanceToken.sol
+++ b/packages/contracts/src/contracts/current/tokens/UnlimitedAllowanceToken/UnlimitedAllowanceToken.sol
@@ -16,9 +16,10 @@
 
 */
 
-pragma solidity ^0.4.18;
+pragma solidity ^0.4.23;
+pragma experimental ABIEncoderV2;
 
-import { ERC20Token } from "../ERC20Token/ERC20Token.sol";
+import "../ERC20Token/ERC20Token.sol";
 
 contract UnlimitedAllowanceToken is ERC20Token {
 
@@ -34,7 +35,18 @@ contract UnlimitedAllowanceToken is ERC20Token {
         returns (bool)
     {
         uint256 allowance = allowed[_from][msg.sender];
-        require(balances[_from] >= _value && allowance >= _value && balances[_to] + _value >= balances[_to]);
+        require(
+            balances[_from] >= _value,
+            "Insufficient balance to complete transfer."
+        );
+        require(
+            allowance >= _value,
+            "Insufficient allowance to complete transfer."
+        );
+        require(
+            balances[_to] + _value >= balances[_to],
+            "Transfer would result in an overflow."
+        );
         balances[_to] += _value;
         balances[_from] -= _value;
         if (allowance < MAX_UINT) {
diff --git a/packages/contracts/src/contracts/current/utils/Authorizable/Authorizable.sol b/packages/contracts/src/contracts/current/utils/Authorizable/Authorizable.sol
index f6032f889..6b84d7aca 100644
--- a/packages/contracts/src/contracts/current/utils/Authorizable/Authorizable.sol
+++ b/packages/contracts/src/contracts/current/utils/Authorizable/Authorizable.sol
@@ -16,7 +16,8 @@
 
 */
 
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
+pragma experimental ABIEncoderV2;
 
 import "./IAuthorizable.sol";
 import "../Ownable/Ownable.sol";
@@ -28,17 +29,26 @@ contract Authorizable is
 
     /// @dev Only authorized addresses can invoke functions with this modifier.
     modifier onlyAuthorized {
-        require(authorized[msg.sender]);
+        require(
+            authorized[msg.sender],
+            "Sender not authorized to call this method."
+        );
         _;
     }
 
     modifier targetAuthorized(address target) {
-        require(authorized[target]);
+        require(
+            authorized[target],
+            "Target address not authorized to call this method."
+        );
         _;
     }
 
     modifier targetNotAuthorized(address target) {
-        require(!authorized[target]);
+        require(
+            !authorized[target],
+            "Target must not already be authorized to call this method."
+        );
         _;
     }
 
@@ -85,8 +95,14 @@ contract Authorizable is
     function removeAuthorizedAddressAtIndex(address target, uint256 index)
         public
     {
-        require(index < authorities.length);
-        require(authorities[index] == target);
+        require(
+            index < authorities.length,
+            "Specified index is out of bounds."
+        );
+        require(
+            authorities[index] == target,
+            "Address found at index does not match target address."
+        );
         delete authorized[target];
         authorities[index] = authorities[authorities.length - 1];
         authorities.length -= 1;
diff --git a/packages/contracts/src/contracts/current/utils/Authorizable/IAuthorizable.sol b/packages/contracts/src/contracts/current/utils/Authorizable/IAuthorizable.sol
index 10c01c6fe..b14cfba22 100644
--- a/packages/contracts/src/contracts/current/utils/Authorizable/IAuthorizable.sol
+++ b/packages/contracts/src/contracts/current/utils/Authorizable/IAuthorizable.sol
@@ -16,7 +16,8 @@
 
 */
 
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
+pragma experimental ABIEncoderV2;
 
 contract IAuthorizable {
 
@@ -44,9 +45,11 @@ contract IAuthorizable {
 
     event AuthorizedAddressAdded(
         address indexed target,
-        address indexed caller);
+        address indexed caller
+    );
 
     event AuthorizedAddressRemoved(
         address indexed target,
-        address indexed caller);
+        address indexed caller
+    );
 }
diff --git a/packages/contracts/src/contracts/current/utils/LibBytes/LibBytes.sol b/packages/contracts/src/contracts/current/utils/LibBytes/LibBytes.sol
index ce107f306..cff780ba4 100644
--- a/packages/contracts/src/contracts/current/utils/LibBytes/LibBytes.sol
+++ b/packages/contracts/src/contracts/current/utils/LibBytes/LibBytes.sol
@@ -16,7 +16,8 @@
 
 */
 
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
+pragma experimental ABIEncoderV2;
 
 contract LibBytes {
 
@@ -61,7 +62,10 @@ contract LibBytes {
         public pure
         returns (address result)
     {
-        require(b.length >= index + 20); // 20 is length of address
+        require(
+            b.length >= index + 20,  // 20 is length of address
+            "Cannot read address from byte array shorter than 20 bytes."
+        ); 
 
         // Add offset to index:
         // 1. Arrays are prefixed by 32-byte length parameter (add 32 to index)
@@ -88,7 +92,10 @@ contract LibBytes {
         address input)
         public pure
     {
-        require(b.length >= index + 20); // 20 is length of address
+        require(
+            b.length >= index + 20,  // 20 is length of address
+            "Cannot write address to byte array shorter than 20 bytes."
+        ); 
 
         // Add offset to index:
         // 1. Arrays are prefixed by 32-byte length parameter (add 32 to index)
@@ -122,7 +129,10 @@ contract LibBytes {
         public pure
         returns (bytes32 result)
     {
-        require(b.length >= index + 32);
+        require(
+            b.length >= index + 32,
+            "Cannot read 32 bytes from byte array shorter than 32 bytes."
+        );
 
         // Arrays are prefixed by a 256 bit length parameter
         index += 32;
@@ -144,7 +154,10 @@ contract LibBytes {
         bytes32 input)
         public pure
     {
-        require(b.length >= index + 32);
+        require(
+            b.length >= index + 32,
+            "Cannot write 32 bytes to byte array shorter than 32 bytes."
+        );
 
         // Arrays are prefixed by a 256 bit length parameter
         index += 32;
diff --git a/packages/contracts/src/contracts/current/utils/Ownable/IOwnable.sol b/packages/contracts/src/contracts/current/utils/Ownable/IOwnable.sol
index 7784a7ba9..63b04945f 100644
--- a/packages/contracts/src/contracts/current/utils/Ownable/IOwnable.sol
+++ b/packages/contracts/src/contracts/current/utils/Ownable/IOwnable.sol
@@ -1,4 +1,5 @@
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
+pragma experimental ABIEncoderV2;
 
 /*
  * Ownable
diff --git a/packages/contracts/src/contracts/current/utils/Ownable/Ownable.sol b/packages/contracts/src/contracts/current/utils/Ownable/Ownable.sol
index 91a5cb7ae..e9b4d6a3b 100644
--- a/packages/contracts/src/contracts/current/utils/Ownable/Ownable.sol
+++ b/packages/contracts/src/contracts/current/utils/Ownable/Ownable.sol
@@ -1,4 +1,5 @@
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
+pragma experimental ABIEncoderV2;
 
 /*
  * Ownable
@@ -12,14 +13,17 @@ import "../Ownable/IOwnable.sol";
 contract Ownable is IOwnable {
     address public owner;
 
-    function Ownable()
+    constructor ()
         public
     {
         owner = msg.sender;
     }
 
     modifier onlyOwner() {
-        require(msg.sender == owner);
+        require(
+            msg.sender == owner,
+            "Only contract owner is allowed to call this method."
+        );
         _;
     }
 
diff --git a/packages/contracts/src/contracts/current/utils/SafeMath/SafeMath.sol b/packages/contracts/src/contracts/current/utils/SafeMath/SafeMath.sol
index 7bd9c2122..1ab27eebc 100644
--- a/packages/contracts/src/contracts/current/utils/SafeMath/SafeMath.sol
+++ b/packages/contracts/src/contracts/current/utils/SafeMath/SafeMath.sol
@@ -1,4 +1,5 @@
-pragma solidity ^0.4.21;
+pragma solidity ^0.4.23;
+pragma experimental ABIEncoderV2;
 
 contract SafeMath {
     function safeMul(uint a, uint b)