BlockLocator

An array of block hashes, starting at the current block, and ending at the genesis block. The creator can skip blocks, populating whatever hashes he feels is most likely to identify a specific chain, closest to the splitoff point. Typically, some kind of exponential backoff is used. For example: The next 10 hashes are the previous 10 blocks (gap 1). After these, the gap is multiplied by 2 for each hash, until the genesis block is added