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In cryptography and computer science, a hash tree or Merkle tree is a tree in which every non-leaf node is labelled with the hash of the labels or values (in case of leaves) of its children nodes. Hash trees are useful because they allow efficient and secure verification of the contents of large data structures. Hash trees are a generalization of hash lists and hash chains. Demonstrating that a leaf node is a part of the given hash tree requires processing an amount of data proportional to the logarithm of the number of nodes of the tree; this contrasts with hash lists, where the amount is proportional to the number of nodes. The concept of hash trees is named after Ralph Merkle who patented it in 1979. ==Uses== Hash trees can be used to verify any kind of data stored, handled and transferred in and between computers. Currently the main use of hash trees is to make sure 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. Suggestions have been made to use hash trees in trusted computing systems.〔J. Kilian. Improved efficient arguments (preliminary version). In CRYPTO, 1995.〕 Hash trees are used in the IPFS and ZFS file systems,〔Jeff Bonwick's Blog ''(ZFS End-to-End Data Integrity )''〕 BitTorrent protocol, Apache Wave protocol,〔Google Wave Federation Protocol ''(Wave Protocol Verification Paper'' )〕 Git distributed revision control system, the Tahoe-LAFS backup system, the Bitcoin peer-to-peer network, the Certificate Transparency framework, and a number of NoSQL systems like Apache Cassandra and Riak. The original purpose of hash trees was to make it possible to efficiently handle many Lamport one-time signatures. Each Lamport key can only be used to sign a single message, but combined with hash trees they can be used for many messages, becoming a fairly efficient digital signature scheme known as a Merkle signature scheme. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Merkle tree」の詳細全文を読む スポンサード リンク
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