/**
     * Fallback function
     *
     * The function without name is the default function that is called whenever anyone sends funds to a contract
     */
    function () payable {
        require(!crowdsaleClosed);
        uint amount = msg.value;
        balanceOf[msg.sender] += amount;
        amountRaised += amount;
        tokenReward.transfer(msg.sender, amount / price);
        FundTransfer(msg.sender, amount, true);
    }

If we generate a 256bits private key k and generate corresponding public key Q.
We could split k in k1 (first 128 bits) and k2 (last 128bits)
Then we generate a set with all 128bits private key and their corresponding public keys.
So, in theory, for each public key in the set:
    we multiply the public key by 2^128
    then, we substract Q to the result
    we test if we have the result in the set
    if yes, we have found k