![]() Similarly, the integrity of data block 元 can be verified if the tree already has hash 1-1 and hash 0. For example, in the picture, the integrity of data block L2 can be verified immediately if the tree already contains hash 0-0 and hash 1 by hashing the data block and iteratively combining the result with hash 0-0 and then hash 1 and finally comparing the result with the top hash. The main difference from a hash list is that one branch of the hash tree can be downloaded at a time and the integrity of each branch can be checked immediately, even though the whole tree is not available yet. Then, the received hash tree is checked against the trusted top hash, and if the hash tree is damaged or fake, another hash tree from another source will be tried until the program finds one that matches the top hash. When the top hash is available, the hash tree can be received from any non-trusted source, like any peer in the p2p network. Before downloading a file on a p2p network, in most cases the top hash is acquired from a trusted source, for instance a friend or a web site that is known to have good recommendations of files to download. In the top of a hash tree there is a top hash (or root hash or master hash). If the hash tree only needs to protect against unintentional damage, unsecured checksums such as CRCs can be used. Usually, a cryptographic hash function such as SHA-2 is used for the hashing. Most hash tree implementations are binary (two child nodes under each node) but they can just as well use many more child nodes under each node. That is, hash 0 = hash( hash(0-0) + hash(0-1) ) where + denotes concatenation. For example, in the above picture hash 0 is the result of hashing the concatenation of hash 0-0 and hash 0-1. Nodes farther up in the tree are the hashes of their respective children. Overview Ī hash tree is a tree of hashes in which the leaves (i.e., leaf nodes, sometimes also called "leafs") are hashes of data blocks in, for instance, a file or set of files. The initial Bitcoin implementation of Merkle trees by Satoshi Nakamoto applies the compression step of the hash function to an excessive degree, which is mitigated by using Fast Merkle Trees. Suggestions have been made to use hash trees in trusted computing systems. Hash trees are also used in the IPFS, Btrfs and ZFS file systems (to counter data degradation ) Dat protocol Apache Wave protocol Git and Mercurial distributed revision control systems the Tahoe-LAFS backup system Zeronet the Bitcoin and Ethereum peer-to-peer networks the Certificate Transparency framework the Nix package manager and descendants like GNU Guix and a number of NoSQL systems such as Apache Cassandra, Riak, and Dynamo. Hash trees are used in hash-based cryptography. They can help ensure that data blocks received from other peers in a peer-to-peer network are received undamaged and unaltered, and even to check that the other peers do not lie and send fake blocks. Hash trees can be used to verify any kind of data stored, handled and transferred in and between computers. The concept of a hash tree is named after Ralph Merkle, who patented it in 1979. A Merkle tree is therefore an efficient example of a cryptographic commitment scheme, in which the root of the tree is seen as a commitment and leaf nodes may be revealed and proven to be part of the original commitment. ![]() Conversely, in a hash list, the number is proportional to the number of leaf nodes itself. A hash tree is a generalization of a hash list and a hash chain.ĭemonstrating that a leaf node is a part of a given binary hash tree requires computing a number of hashes proportional to the logarithm of the number of leaf nodes in the tree. A hash tree allows efficient and secure verification of the contents of a large data structure. In cryptography and computer science, a hash tree or Merkle tree is a tree in which every "leaf" ( node) is labelled with the cryptographic hash of a data block, and every node that is not a leaf (called a branch, inner node, or inode) is labelled with the cryptographic hash of the labels of its child nodes. Hashes 0-0 and 0-1 are the hash values of data blocks L1 and L2, respectively, and hash 0 is the hash of the concatenation of hashes 0-0 and 0–1.
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