From 6600ee5ccf12c8591299bb3ffdf4355ac54dae21 Mon Sep 17 00:00:00 2001
From: Ricardo Guilherme Schmidt <3esmit@gmail.com>
Date: Thu, 26 Apr 2018 01:03:55 -0300
Subject: [PATCH] add basic ethereum signing message methods

---
 contracts/common/MessageSigned.sol | 77 ++++++++++++++++++++++++++++++
 1 file changed, 77 insertions(+)
 create mode 100644 contracts/common/MessageSigned.sol

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