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myarbrough@oreilly.com 2014-11-18 08:37:37 -08:00
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@ -53,7 +53,7 @@ The nonce, difficulty target, and timestamp are used in the mining process and w
[[block_hash]]
=== Block Identifiers: Block Header Hash and Block Height
((("blocks","header hash")))((("blocks","height")))((("blocks","identifiers")))The primary identifier of a block is its cryptographic hash, a digital fingerprint, made by hashing the block header twice through the SHA256 algorithm. The resulting 32-byte hash, is called the((("block hash")))((("block header hash"))) _block hash_ but is more accurately the _block header hash_, because only the block header is used to compute it. For example, the block hash of the first bitcoin block ever created is the following: +000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f+. The block hash identifies a block uniquely and unambiguously and can be independently derived by any node by simply hashing the block header.
((("blocks","header hash")))((("blocks","height")))((("blocks","identifiers")))The primary identifier of a block is its cryptographic hash, a digital fingerprint, made by hashing the block header twice through the SHA256 algorithm. The resulting 32-byte hash is called the((("block hash")))((("block header hash"))) _block hash_ but is more accurately the _block header hash_, because only the block header is used to compute it. For example, +000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f+ is the block hash of the first bitcoin block ever created. The block hash identifies a block uniquely and unambiguously and can be independently derived by any node by simply hashing the block header.
Note that the block hash is not actually included inside the block's data structure, neither when the block is transmitted on the network, nor when it is stored on a node's persistence storage as part of the blockchain. Instead, the block's hash is computed by each node as the block is received from the network. The block hash may be stored in a separate database table as part of the block's metadata, to facilitate indexing and faster retrieval of blocks from disk.