While the light client sync protocol currently provides access to the
latest `BeaconBlockHeader`, obtaining the matching execution data needs
workarounds such as downloading the full block.
Having ready access to the EL state root simplifies use cases that need
a way to cross-check `eth_getProof` responses against LC data.
Access to `block_hash` unlocks scenarios where a CL light client drives
an EL without `engine_newPayload`. As of Altair, only the CL beacon
block root is available, but the EL block hash is needed for engine API.
Other fields in the `ExecutionPayloadHeader` such as `logs_bloom` may
allow light client applications to monitor blocks for local interest,
e.g. for transfers affecting a certain wallet. This enables to download
only the few relevant blocks instead of every single one.
A new `LightClientStore` is proposed into the Capella spec that may be
used to sync LC data that includes execution data. Existing pre-Capella
LC data will remain as is, but can be locally upgraded before feeding it
into the new `LightClientStore` so that light clients do not need to run
a potentially expensive fork transition at a specific time. This enables
the `LightClientStore` to be upgraded at a use case dependent timing at
any time before Capella hits. Smart contract and embedded deployments
benefit from reduced code size and do not need synchronization with the
beacon chain clock to perform the Capella fork.
This commit changes the public API of the KZG library to the following high-level API:
```
- verify_kzg_proof()
- compute_aggregate_kzg_proof()
- verify_aggregate_kzg_proof()
- blob_to_kzg_commitment()
```
compared to the previous much more low-level API:
```
- compute_powers()
- matrix_lincomb()
- lincomb()
- bytes_to_bls_field()
- evaluate_polynomial_in_evaluation_form()
- verify_kzg_proof()
- compute_kzg_proof()
```
This means that all the cryptographic logic (including Fiat-Shamir) is now isolated and hidden in the KZG library and the `validator.md` file ends up being significantly simplified, only calling high-level KZG functions.
Some additional things that this commit does:
- Moves all EIP4844 cryptography into polynomial-commitments.md
- Improves the Fiat-Shamir stack by removing the need for SSZ and by introducing simple domain separators
Co-authored-by: Kevaundray Wedderburn <kevtheappdev@gmail.com>
Co-authored-by: Hsiao-Wei Wang <hsiaowei.eth@gmail.com>
Co-authored-by: Dankrad Feist <mail@dankradfeist.de>
`remerkleable` was updated to address potentially incorrect computation
of `hash_tree_root` against default-initialized `Vector` objects.
Switching to the fixed version.
While the current Altair specs define structures to aid light client
development, one missing key aspect is the network protocol definition.
Certain implementations have started defining their own REST based APIs,
e.g., Lodestar at https://github.com/ChainSafe/lodestar/blob/master/packages/api/src/routes/lightclient.ts
While such APIs are useful, REST does not seem to be the ideomatic
choice as the sole API available at such a low level for Ethereum.
This patch introduces a libp2p based protocol to allow light clients to
sync to the latest `BeaconBlockHeader` in a trustless and decentralized
manner, building on top of prior work from:
- @hwwhww at https://github.com/ethereum/consensus-specs/pull/2267
- @jinfwhuang at https://github.com/ethereum/consensus-specs/pull/2786
- Lodestar's REST API (also has an endpoint to fetch merkle proofs!)
Adds `create_light_client_bootstrap` and `create_light_client_update`
functions as a reference implementation for serving light client data.
This also enables a new test harness to verify that light client data
gets applied to a `LightClientStore` as expected.
- Implement all the required glue code to make things executable
- Implement a dummy KZG trusted setup
Co-authored-by: Hsiao-Wei Wang <hsiaowei.eth@gmail.com>
Introduces a new `LightClientBootstrap` structure to allow setting up a
`LightClientStore` with the initial sync committee and block header from
a user-configured trusted block root.
This leads to new cases where the `LightClientStore` is only aware of
the current but not the next sync committee. As a side effect of these
new cases, the store's `finalized_header` may now advance into the next
sync committee period before a corresponding `LightClientUpdate` with
the new sync committee is obtained, improving responsiveness.
Note that so far, `LightClientUpdate.attested_header.slot` needed to be
newer than `LightClientStore.finalized_header.slot`. However, it is now
necessary to also consider certain older updates to try and backfill the
`next_sync_committee`. The `is_better_update` helper is also updated to
improve `best_valid_update` tracking.
Etan Kissling
Danny Ryan
Hsiao-Wei Wang
inphi
George Kadianakis
Alex Stokes
ChihChengLiang
Mikhail Kalinin