Here is an alternate algorithm, based on mcherm's suggestion. Choose a publicly available number, such as NYSE closing price, that is not revealed until after the lottery closes. The hash of this is the target. The exact format of what is hashed is announced in advance.
All purchasers' bitcoin addresses are posted publicly, in the order they come in. They are salted with the ticket number, i.e. mybitcoinaddress-001 represents the first ticket I bought. All of these addresses (including salt) are hashed. The one that is closest to the target is the winner. Closeness can be measured as integers (absolute value) with ties possible but extremely unlikely.
All purchasers' bitcoin addresses are posted publicly, in the order they come in. They are salted with the ticket number, i.e. mybitcoinaddress-001 represents the first ticket I bought. All of these addresses (including salt) are hashed. The one that is closest to the target is the winner. Closeness can be measured as integers (absolute value) with ties possible but extremely unlikely.