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This change begins the work of bringing committed filters to the network consensus daemon. Committed filters are designed to enable light wallets without many of the privacy issues associated with server-side bloom filtering. The new gcs package provides the primitives for creating and matching against Golomb-coded sets (GCS) filters while the blockcf package provides creation of filters and filter entries for data structures found in blocks. The wire package has been updated to define a new protocol version and service flag for advertising CF support and includes types for the following new messages: cfheaders, cfilter, cftypes, getcfheaders, getcfilter, getcftypes. The peer package and server implementation have been updated to include support for the new protocol version and messages. Filters are created using a collision probability of 2^-20 and are saved to a new optional database index when running with committed filter support enabled (the default). At first startup, if support is not disabled, the index will be created and populated with filters and filter headers for all preexisting blocks, and new filters will be recorded for processed blocks. Multiple filter types are supported. The regular filter commits to output scripts and previous outpoints that any non-voting wallet will require access to. Scripts and previous outpoints that can only be spent by votes and revocations are not committed to the filter. The extended filter is a supplementary filter which commits to all transaction hashes and script data pushes from the input scripts of non-coinbase regular and ticket purchase transactions. Creating these filters is based on the algorithm defined by BIP0158 but is modified to only commit "regular" data in stake transactions to prevent committed filters from being used to create SPV voting wallets.
27 lines
1.0 KiB
Go
27 lines
1.0 KiB
Go
// Copyright (c) 2016-2017 The btcsuite developers
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// Copyright (c) 2016-2017 The Lightning Network Developers
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// Copyright (c) 2018 The Decred developers
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// Use of this source code is governed by an ISC
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// license that can be found in the LICENSE file.
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/*
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Package gcs provides an API for building and using a Golomb-coded set filter.
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Golomb-Coded Set
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A Golomb-coded set is a probabilistic data structure used similarly to a Bloom
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filter. A filter uses constant-size overhead plus on average n+2 bits per item
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added to the filter, where 2^-n is the desired false positive (collision)
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probability.
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GCS use in Decred
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GCS filters are a mechanism for storing and transmitting per-block filters. The
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usage is intended to be the inverse of Bloom filters: a consensus-validating
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full node commits to a single filter for every block and serves the filter to
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SPV clients that match against the filter locally to determine if the block is
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potentially relevant. The suggested collision probability for Decred use is
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2^-20.
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*/
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package gcs
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