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/token/ERC20Token.sol b/contracts/token/ERC20Token.sol
index 63678ea..ff8de15 100644
--- a/contracts/token/ERC20Token.sol
+++ b/contracts/token/ERC20Token.sol
@@ -4,36 +4,48 @@ pragma solidity ^0.4.23;
 // https://github.com/ethereum/EIPs/issues/20
 
 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
+
+    /**
+     * @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
+    /**
+     * @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
+    /**
+     * @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
+    /**
+     * @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
+    /**
+     * @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);
 
-    /// total amount of tokens
+    /**
+     * @notice return total supply of tokens
+     */
     function totalSupply() external view returns (uint256 supply);
 
     event Transfer(address indexed _from, address indexed _to, uint256 _value);