The University of SydneyPage 23Constructing a block–Merkle tree–Pair transactions and calculate double-SHA hash until there is only one hash, or the merkelroot.•HA= SHA256(SHA256(Transaction A))–Can check if any transaction is included in the tree with at most 2log2(N) hash calculations.–This allows Wallet nodes to check whether transactions are included in a block without downloading the whole block.