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light: expand on errors and docs (#5443)

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Callum Waters
2020-10-02 20:05:15 +02:00
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parent bf9e36d02d
commit a4b7018732
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docs/tendermint-core/light-client.md
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@@ -13,9 +13,10 @@ package](https://pkg.go.dev/github.com/tendermint/tendermint/light?tab=doc).
## Overview
The objective of the light client protocol is to get a commit for a recent
block hash where the commit includes a majority of signatures from the last
known validator set. From there, all the application state is verifiable with
The light client protocol verifies headers by retrieving a chain of headers,
commits and validator sets from a trusted height to the target height, verifying
the signatures of each of these intermediary signed headers till it reaches the
target height. From there, all the application state is verifiable with
[merkle proofs](https://github.com/tendermint/spec/blob/953523c3cb99fdb8c8f7a2d21e3a99094279e9de/spec/blockchain/encoding.md#iavl-tree).
## Properties
@@ -30,11 +31,29 @@ known validator set. From there, all the application state is verifiable with
name-registry without worrying about fork censorship attacks, without posting
a commit and waiting for confirmations. It's fast, secure, and free!
## Security
A light client is initialized from a point of trust using [Trust Options](https://pkg.go.dev/github.com/tendermint/tendermint/light?tab=doc#TrustOptions),
a provider and a set of witnesses. This sets the trust period: the period that
full nodes should be accountable for faulty behavior and a trust level: the
fraction of validators in a validator set with which we trust that at least one
is correct. As Tendermint consensus can withstand 1/3 byzantine faults, this is
the default trust level, however, for greater security you can increase it (max:
1).
Similar to a full node, light clients can also be subject to byzantine attacks.
A light client also runs a detector process which cross verifies headers from a
primary with witnesses. Therefore light clients should be set with enough witnesses.
If the light client observes a faulty provider it will report it to another provider
and return an error.
In summary, the light client is not safe when a) more than the trust level of
validators are malicious and b) all witnesses are malicious.
## Where to obtain trusted height & hash
[Trust Options](https://pkg.go.dev/github.com/tendermint/tendermint/light?tab=doc#TrustOptions)
One way to obtain semi-trusted hash & height is to query multiple full nodes
One way to obtain a semi-trusted hash & height is to query multiple full nodes
and compare their hashes:
```bash