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pragma solidity ^0.4.11;
import "../Oracles/Oracle.sol";
/// @title Signed message oracle contract - Allows to set an outcome with a signed message
/// @author Stefan George - <stefan@gnosis.pm>
contract SignedMessageOracle is Oracle {
/*
* Events
*/
event SignerReplacement(address indexed newSigner);
event OutcomeAssignment(int outcome);
/*
* Storage
*/
address public signer;
bytes32 public descriptionHash;
uint nonce;
bool public isSet;
int public outcome;
/*
* Modifiers
*/
modifier isSigner () {
// Only signer is allowed to proceed
require(msg.sender == signer);
_;
}
/*
* Public functions
*/
/// @dev Constructor sets signer address based on signature
/// @param _descriptionHash Hash identifying off chain event description
/// @param v Signature parameter
/// @param r Signature parameter
/// @param s Signature parameter
constructor(bytes32 _descriptionHash, uint8 v, bytes32 r, bytes32 s)
public
{
signer = ecrecover(_descriptionHash, v, r, s);
descriptionHash = _descriptionHash;
}
/// @dev Replaces signer
/// @param newSigner New signer
/// @param _nonce Unique nonce to prevent replay attacks
/// @param v Signature parameter
/// @param r Signature parameter
/// @param s Signature parameter
function replaceSigner(address newSigner, uint _nonce, uint8 v, bytes32 r, bytes32 s)
public
isSigner
{
// Result is not set yet and nonce and signer are valid
require( !isSet
&& _nonce > nonce
&& signer == ecrecover(keccak256(abi.encodePacked(descriptionHash, newSigner, _nonce)), v, r, s));
nonce = _nonce;
signer = newSigner;
emit SignerReplacement(newSigner);
}
/// @dev Sets outcome based on signed message
/// @param _outcome Signed event outcome
/// @param v Signature parameter
/// @param r Signature parameter
/// @param s Signature parameter
function setOutcome(int _outcome, uint8 v, bytes32 r, bytes32 s)
public
{
// Result is not set yet and signer is valid
require( !isSet
&& signer == ecrecover(keccak256(abi.encodePacked(descriptionHash, _outcome)), v, r, s));
isSet = true;
outcome = _outcome;
emit OutcomeAssignment(_outcome);
}
/// @dev Returns if winning outcome
/// @return Is outcome set?
function isOutcomeSet()
public
constant
returns (bool)
{
return isSet;
}
/// @dev Returns winning outcome
/// @return Outcome
function getOutcome()
public
constant
returns (int)
{
return outcome;
}
}
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