diff --git a/contracts/common/Controlled.sol b/contracts/common/Controlled.sol
index d2773f3..7b615b6 100644
--- a/contracts/common/Controlled.sol
+++ b/contracts/common/Controlled.sol
@@ -10,7 +10,7 @@ contract Controlled {
 
     address public controller;
 
-    constructor() public { 
+    constructor() internal { 
         controller = msg.sender; 
     }
 
diff --git a/contracts/common/MessageSigned.sol b/contracts/common/MessageSigned.sol
new file mode 100644
index 0000000..5a5a262
--- /dev/null
+++ b/contracts/common/MessageSigned.sol
@@ -0,0 +1,77 @@
+pragma solidity ^0.4.21;
+
+/** 
+ * @notice Uses ethereum signed messages
+ */
+contract MessageSigned {
+    
+    constructor() internal {
+
+    }
+
+    /**
+     * @notice recovers address who signed the message
+     * @param _signHash operation ethereum signed message hash
+     * @param _messageSignature message `_signHash` signature
+     */
+    function recoverAddress(
+        bytes32 _signHash, 
+        bytes _messageSignature
+    )
+        pure
+        internal
+        returns(address) 
+    {
+        uint8 v;
+        bytes32 r;
+        bytes32 s;
+        (v,r,s) = signatureSplit(_messageSignature);
+        return ecrecover(
+            _signHash,
+            v,
+            r,
+            s
+        );
+    }
+
+    /**
+     * @notice Hash a hash with `"\x19Ethereum Signed Message:\n32"`
+     * @param _hash Sign to hash.
+     * @return signHash Hash to be signed.
+     */
+    function getSignHash(
+        bytes32 _hash
+    )
+        pure
+        internal
+        returns (bytes32 signHash)
+    {
+        signHash = keccak256("\x19Ethereum Signed Message:\n32", _hash);
+    }
+
+    /**
+     * @dev divides bytes signature into `uint8 v, bytes32 r, bytes32 s` 
+     */
+    function signatureSplit(bytes _signature)
+        pure
+        internal
+        returns (uint8 v, bytes32 r, bytes32 s)
+    {
+        // The signature format is a compact form of:
+        //   {bytes32 r}{bytes32 s}{uint8 v}
+        // Compact means, uint8 is not padded to 32 bytes.
+        assembly {
+            r := mload(add(_signature, 32))
+            s := mload(add(_signature, 64))
+            // Here we are loading the last 32 bytes, including 31 bytes
+            // of 's'. There is no 'mload8' to do this.
+            //
+            // 'byte' is not working due to the Solidity parser, so lets
+            // use the second best option, 'and'
+            v := and(mload(add(_signature, 65)), 0xff)
+        }
+
+        require(v == 27 || v == 28);
+    }
+    
+}
\ No newline at end of file
diff --git a/contracts/common/Owned.sol b/contracts/common/Owned.sol
index 177bf0f..18f03e7 100644
--- a/contracts/common/Owned.sol
+++ b/contracts/common/Owned.sol
@@ -14,7 +14,7 @@ contract Owned {
     address public owner;
 
     /// @notice The Constructor assigns the message sender to be `owner`
-    constructor() public {
+    constructor() internal {
         owner = msg.sender;
     }
 
diff --git a/contracts/token/ERC20Token.sol b/contracts/token/ERC20Token.sol
index c210342..ff8de15 100644
--- a/contracts/token/ERC20Token.sol
+++ b/contracts/token/ERC20Token.sol
@@ -1,48 +1,52 @@
-pragma solidity ^0.4.17;
+pragma solidity ^0.4.23;
 
 // Abstract contract for the full ERC 20 Token standard
 // https://github.com/ethereum/EIPs/issues/20
 
-contract ERC20Token {
-    /* This is a slight change to the ERC20 base standard.
-    function totalSupply() constant returns (uint256 supply);
-    is replaced with:
-    uint256 public totalSupply;
-    This automatically creates a getter function for the totalSupply.
-    This is moved to the base contract since public getter functions are not
-    currently recognised as an implementation of the matching abstract
-    function by the compiler.
-    */
-    /// total amount of tokens
-    uint256 public totalSupply;
+interface ERC20Token {
 
-    /// @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
-    function transfer(address _to, uint256 _value) public returns (bool success);
+    /**
+     * @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
+     */
+    function transfer(address _to, uint256 _value) external returns (bool success);
 
-    /// @notice `msg.sender` approves `_spender` to spend `_value` tokens
-    /// @param _spender The address of the account able to transfer the tokens
-    /// @param _value The amount of tokens to be approved for transfer
-    /// @return Whether the approval was successful or not
-    function approve(address _spender, uint256 _value) public returns (bool success);
+    /**
+     * @notice `msg.sender` approves `_spender` to spend `_value` tokens
+     * @param _spender The address of the account able to transfer the tokens
+     * @param _value The amount of tokens to be approved for transfer
+     * @return Whether the approval was successful or not
+     */
+    function approve(address _spender, uint256 _value) external returns (bool success);
 
-    /// @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
-    /// @return Whether the transfer was successful or not
-    function transferFrom(address _from, address _to, uint256 _value) public returns (bool success);
+    /**
+     * @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
+     * @return Whether the transfer was successful or not
+     */
+    function transferFrom(address _from, address _to, uint256 _value) external returns (bool success);
 
-    /// @param _owner The address from which the balance will be retrieved
-    /// @return The balance
-    function balanceOf(address _owner) public view returns (uint256 balance);
+    /**
+     * @param _owner The address from which the balance will be retrieved
+     * @return The balance
+     */
+    function balanceOf(address _owner) external view returns (uint256 balance);
 
-    /// @param _owner The address of the account owning tokens
-    /// @param _spender The address of the account able to transfer the tokens
-    /// @return Amount of remaining tokens allowed to spent
-    function allowance(address _owner, address _spender) public view returns (uint256 remaining);
+    /**
+     * @param _owner The address of the account owning tokens
+     * @param _spender The address of the account able to transfer the tokens
+     * @return Amount of remaining tokens allowed to spent
+     */
+    function allowance(address _owner, address _spender) external view returns (uint256 remaining);
+
+    /**
+     * @notice return total supply of tokens
+     */
+    function totalSupply() external view returns (uint256 supply);
 
     event Transfer(address indexed _from, address indexed _to, uint256 _value);
     event Approval(address indexed _owner, address indexed _spender, uint256 _value);
diff --git a/contracts/token/StandardToken.sol b/contracts/token/StandardToken.sol
index 10ca74a..d42852c 100644
--- a/contracts/token/StandardToken.sol
+++ b/contracts/token/StandardToken.sol
@@ -4,23 +4,24 @@ import "./ERC20Token.sol";
 
 contract StandardToken is ERC20Token {
 
+    uint256 private supply;
     mapping (address => uint256) balances;
     mapping (address => mapping (address => uint256)) allowed;
 
     constructor() internal { }
-
+    
     function transfer(
         address _to,
         uint256 _value
     ) 
-        public 
+        external 
         returns (bool success)
     {
         return transfer(msg.sender, _to, _value);    
     }
 
     function approve(address _spender, uint256 _value) 
-        public
+        external
         returns (bool success) 
     {
         allowed[msg.sender][_spender] = _value;
@@ -33,7 +34,7 @@ contract StandardToken is ERC20Token {
         address _to,
         uint256 _value
     )
-        public
+        external
         returns (bool success)
     {
         if (balances[_from] >= _value &&
@@ -47,7 +48,7 @@ contract StandardToken is ERC20Token {
     }
 
     function allowance(address _owner, address _spender) 
-        public 
+        external 
         view 
         returns (uint256 remaining)
     {
@@ -55,12 +56,31 @@ contract StandardToken is ERC20Token {
     }
 
     function balanceOf(address _owner) 
-        public 
+        external 
         view 
         returns (uint256 balance) 
     {
         return balances[_owner];
     }
+    
+    function totalSupply() 
+        external 
+        view 
+        returns(uint256 supply) 
+    {
+        return supply;
+    }
+
+    function mint(
+        address _to,
+        uint256 _amount
+    ) 
+        internal
+    {
+        balances[_to] += _amount;
+        supply += _amount;
+        emit Transfer(0x0, _to, _amount);
+    }
 
     function transfer(
         address _from, 
diff --git a/contracts/token/TestToken.sol b/contracts/token/TestToken.sol
new file mode 100644
index 0000000..2afff21
--- /dev/null
+++ b/contracts/token/TestToken.sol
@@ -0,0 +1,19 @@
+pragma solidity ^0.4.23;
+
+import "./StandardToken.sol";
+
+/**
+ * @notice ERC20Token for test scripts, can be minted by anyone.
+ */
+contract TestToken is StandardToken {
+    
+    constructor() public { }
+
+    /**
+     * @notice any caller can mint any `_amount` 
+     * @param _amount how much to be minted
+     */
+    function mint(uint256 _amount) public {
+        mint(msg.sender, _amount);
+    }
+}