ether-poe.sol

pragma solidity ^0.4.20;

contract poe {
    mapping(string => uint) proof;
    event Exists(string data, uint blockNumber);

    function prove(string data) constant public returns (uint) {
        return proof[data];
    }

    function upload(string data) public{
        require (proof[data] == 0);
        proof[data] = block.number;
        emit Exists(data, block.number);
    }
}