Merkle tree

In the cryptography used in a blockchain, there is a fourth capability that ensures that the data is still valid, and that is a Merkle tree. The Merkle tree, or hash tree, is a tree of data blocks in which every leaf node is labeled by a hash or digital signature, and every non-leaf node (for example, the top of the tree) is labelled with the cryptographic hash of all of the digital signatures of its child nodes as its input. The hash tree is used by the blockchain to verify all data that is stored, processed, and transferred between nodes in the network. It can ensure that the blocks received from other nodes (peers) in the network are undamaged and unaltered, and it can verify that other peers do not send malicious data blocks and lie about their content. More details about these capabilities will be presented in Chapter 3, Blockchain 101 - Assets, Transactions, and Hashes.