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Edited ch08.asciidoc with Atlas code editor

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nadams 2017-05-18 08:17:41 -07:00
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@ -194,12 +194,12 @@ A full blockchain node verifies a transaction by checking the entire chain of th
To get the block headers, SPV nodes use a +getheaders+ message instead of +getblocks+. The responding peer will send up to 2,000 block headers using a single +headers+ message. The process is otherwise the same as that used by a full node to retrieve full blocks. SPV nodes also set a filter on the connection to peers, to filter the stream of future blocks and transactions sent by the peers. Any transactions of interest are retrieved using a +getdata+ request. The peer generates a +tx+ message containing the transactions, in response. <<spv_synchronization>> shows the synchronization of block headers.
Because SPV nodes need to retrieve specific transactions in order to selectively verify them, they also create a privacy risk. Unlike full blockchain nodes, which collect all transactions within each block, the SPV node's requests for specific data can inadvertently reveal the addresses in their wallet. For example, a third party monitoring a network could keep track of all the transactions requested by a wallet on an SPV node and use those to associate bitcoin addresses with the user of that wallet, destroying the user's privacy.
[[spv_synchronization]]
.SPV node synchronizing the block headers
image::images/mbc2_0807.png["SPVSynchronization"]
Because SPV nodes need to retrieve specific transactions in order to selectively verify them, they also create a privacy risk. Unlike full blockchain nodes, which collect all transactions within each block, the SPV node's requests for specific data can inadvertently reveal the addresses in their wallet. For example, a third party monitoring a network could keep track of all the transactions requested by a wallet on an SPV node and use those to associate bitcoin addresses with the user of that wallet, destroying the user's privacy.
Shortly after the introduction of SPV/lightweight nodes, bitcoin developers added a feature called _bloom filters_ to address the privacy risks of SPV nodes. Bloom filters allow SPV nodes to receive a subset of the transactions without revealing precisely which addresses they are interested in, through a filtering mechanism that uses probabilities rather than fixed patterns.((("", startref="BNspvnodes08")))((("", startref="simple08")))
[[bloom_filters]]