signing prefix added

contracts/ECRecovery.sol

@@ -0,0 +1,54 @@
+pragma solidity ^0.4.18;
+
+
+/**
+ * @title Eliptic curve signature operations
+ *
+ * @dev Based on https://gist.github.com/axic/5b33912c6f61ae6fd96d6c4a47afde6d
+ */
+
+library ECRecovery {
+
+  /**
+   * @dev Recover signer address from a message by using his signature
+   * @param hash bytes32 message, the hash is the signed message. What is recovered is the signer address.
+   * @param sig bytes signature, the signature is generated using web3.eth.sign()
+   */
+  function recover(bytes32 hash, bytes sig) public pure returns (address) {
+    bytes32 r;
+    bytes32 s;
+    uint8 v;
+
+    //Check the signature length
+    if (sig.length != 65) {
+      return (address(0));
+    }
+
+    // Divide the signature in r, s and v variables
+    assembly {
+      r := mload(add(sig, 32))
+      s := mload(add(sig, 64))
+      v := byte(0, mload(add(sig, 96)))
+    }
+
+    // Version of signature should be 27 or 28, but 0 and 1 are also possible versions
+    if (v < 27) {
+      v += 27;
+    }
+
+    // If the version is correct return the signer address
+    if (v != 27 && v != 28) {
+      return (address(0));
+    } else {
+	   
+	   /* 
+        * https://github.com/ethereum/go-ethereum/issues/3731
+        */
+		
+      bytes memory prefix = "\x19Ethereum Signed Message:\n32";
+      hash = keccak256(prefix, hash);
+      return ecrecover(hash, v, r, s);
+    }
+  }
+
+}