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44 lines
2.0 KiB
Go
44 lines
2.0 KiB
Go
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// Package slasher defines an optimized implementation of Ethereum proof-of-stake slashing
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// detection, namely focused on catching "surround vote" slashable
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// offenses as explained here: https://blog.ethereum.org/2020/01/13/validated-staking-on-eth2-1-incentives/.
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//
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// Surround vote detection is a difficult problem if done naively, as slasher
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// needs to keep track of every single attestation by every single validator
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// in the network and be ready to efficiently detect whether incoming attestations
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// are slashable with respect to older ones. To do this, the Sigma Prime team
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// created an elaborate design document: https://hackmd.io/@sproul/min-max-slasher
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// offering an optimal solution.
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//
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// Attesting histories are kept for each validator in two separate arrays known
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// as min and max spans, which are explained in our design document:
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// https://hackmd.io/@prysmaticlabs/slasher.
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//
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// A regular pair of min and max spans for a validator look as follows
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// with length = H where H is the amount of epochs worth of history
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// we want to persist for slashing detection.
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//
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// validator_1_min_span = [2, 2, 2, ..., 2]
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// validator_1_max_span = [0, 0, 0, ..., 0]
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//
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// Instead of always dealing with length H arrays, which can be prohibitively
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// expensive to handle in memory, we split these arrays into chunks of length C.
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// For C = 3, for example, the 0th chunk of validator 1's min and max spans would look
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// as follows:
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//
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// validator_1_min_span_chunk_0 = [2, 2, 2]
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// validator_1_max_span_chunk_0 = [2, 2, 2]
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//
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// Next, on disk, we take chunks for K validators, and store them as flat slices.
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// For example, if H = 3, C = 3, and K = 3, then we can store 3 validators' chunks as a flat
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// slice as follows:
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//
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// val0 val1 val2
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// | | |
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// { } { } { }
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// [2, 2, 2, 2, 2, 2, 2, 2, 2]
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//
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// This is known as 2D chunking, pioneered by the Sigma Prime team here:
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// https://hackmd.io/@sproul/min-max-slasher. The parameters H, C, and K will be
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// used extensively throughout this package.
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package slasher
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