Adopt EIP-7688: Forward compatible consensus data structures

EIP-4788 exposes the beacon root to smart contracts, but smart contracts
using it need to be redeployed / upgraded whenever the indexing changes
during a fork, even if that fork does not touch any used functionality.

This problem expands further to bridges on other blockchains, or even
into wallet apps on a phone that verify data from the beacon chain
instead of trusting the server. It is quite unrealistic to expect such
projects to all align their release cadence with Ethereum's forks.

EIP-7688 fixes this by defining forward compatibility for beacon chain
data structures. Electra `Profile` retain their Merkleization even when
rebased to `StableContainer` definitions from future forks, enabling
decentralized protocols to drop the requirement for trusted parties to
periodically upgrade beacon state proof verifiers.

Author: etan-status

presets/mainnet/electra.yaml

@@ -48,3 +48,8 @@ MAX_PENDING_PARTIALS_PER_WITHDRAWALS_SWEEP: 8
 # ---------------------------------------------------------------
 # 2**4 ( = 4) pending deposits
 MAX_PENDING_DEPOSITS_PER_EPOCH: 16
+
+# Misc
+# ---------------------------------------------------------------
+# `floorlog2(get_generalized_index(BeaconBlockBody, 'blob_kzg_commitments')) + 1 + ceillog2(MAX_BLOB_COMMITMENTS_PER_BLOCK)` = 7 + 1 + 12 = 20
+KZG_COMMITMENT_INCLUSION_PROOF_DEPTH_ELECTRA: 20

presets/minimal/electra.yaml

@@ -48,3 +48,8 @@ MAX_PENDING_PARTIALS_PER_WITHDRAWALS_SWEEP: 2
 # ---------------------------------------------------------------
 # 2**4 ( = 4) pending deposits
 MAX_PENDING_DEPOSITS_PER_EPOCH: 16
+
+# Misc
+# ---------------------------------------------------------------
+# [customized] `floorlog2(get_generalized_index(BeaconBlockBody, 'blob_kzg_commitments')) + 1 + ceillog2(MAX_BLOB_COMMITMENTS_PER_BLOCK)` = 7 + 1 + 4 = 12
+KZG_COMMITMENT_INCLUSION_PROOF_DEPTH_ELECTRA: 12

pysetup/spec_builders/deneb.py

@@ -87,10 +87,5 @@ def hardcoded_custom_type_dep_constants(cls, spec_object) -> Dict[str, str]:
             'FIELD_ELEMENTS_PER_BLOB': spec_object.preset_vars['FIELD_ELEMENTS_PER_BLOB'].value,
             'MAX_BLOBS_PER_BLOCK': spec_object.config_vars['MAX_BLOBS_PER_BLOCK'].value,
             'MAX_BLOB_COMMITMENTS_PER_BLOCK': spec_object.preset_vars['MAX_BLOB_COMMITMENTS_PER_BLOCK'].value,
-        }
-
-    @classmethod
-    def hardcoded_func_dep_presets(cls, spec_object) -> Dict[str, str]:
-        return {
             'KZG_COMMITMENT_INCLUSION_PROOF_DEPTH': spec_object.preset_vars['KZG_COMMITMENT_INCLUSION_PROOF_DEPTH'].value,
         }

pysetup/spec_builders/electra.py

@@ -11,14 +11,22 @@ def imports(cls, preset_name: str):
         return f'''
 from eth2spec.deneb import {preset_name} as deneb
 from eth2spec.utils.ssz.ssz_impl import serialize
+from eth2spec.utils.ssz.ssz_typing import StableContainer, Profile
 '''
 
     @classmethod
     def hardcoded_ssz_dep_constants(cls) -> Dict[str, str]:
         return {
-            'FINALIZED_ROOT_GINDEX_ELECTRA': 'GeneralizedIndex(169)',
-            'CURRENT_SYNC_COMMITTEE_GINDEX_ELECTRA': 'GeneralizedIndex(86)',
-            'NEXT_SYNC_COMMITTEE_GINDEX_ELECTRA': 'GeneralizedIndex(87)',
+            'FINALIZED_ROOT_GINDEX_ELECTRA': 'GeneralizedIndex(553)',
+            'CURRENT_SYNC_COMMITTEE_GINDEX_ELECTRA': 'GeneralizedIndex(278)',
+            'NEXT_SYNC_COMMITTEE_GINDEX_ELECTRA': 'GeneralizedIndex(279)',
+            'EXECUTION_PAYLOAD_GINDEX_ELECTRA': 'GeneralizedIndex(137)',
+        }
+
+    @classmethod
+    def hardcoded_custom_type_dep_constants(cls, spec_object) -> Dict[str, str]:
+        return {
+            'KZG_COMMITMENT_INCLUSION_PROOF_DEPTH_ELECTRA': spec_object.preset_vars['KZG_COMMITMENT_INCLUSION_PROOF_DEPTH_ELECTRA'].value,
         }
 
 
@@ -57,4 +65,4 @@ def verify_and_notify_new_payload(self: ExecutionEngine,
         return True
 
 
-EXECUTION_ENGINE = NoopExecutionEngine()"""
+EXECUTION_ENGINE = NoopExecutionEngine()"""

setup.py

@@ -571,7 +571,7 @@ def run(self):
         "pycryptodome>=3.19.1",
         "py_ecc==6.0.0",
         "milagro_bls_binding==1.9.0",
-        "remerkleable==0.1.28",
+        "remerkleable @ git+https://github.com/etan-status/remerkleable@dev/etan/sc-default",
         "trie==2.0.2",
         RUAMEL_YAML_VERSION,
         "lru-dict==1.2.0",

specs/capella/light-client/full-node.md

@@ -47,7 +47,7 @@ def block_to_light_client_header(block: SignedBeaconBlock) -> LightClientHeader:
             withdrawals_root=hash_tree_root(payload.withdrawals),
         )
         execution_branch = ExecutionBranch(
-            compute_merkle_proof(block.message.body, EXECUTION_PAYLOAD_GINDEX))
+            compute_merkle_proof(block.message.body, execution_payload_gindex_at_slot(block.message.slot)))
     else:
         # Note that during fork transitions, `finalized_header` may still point to earlier forks.
         # While Bellatrix blocks also contain an `ExecutionPayload` (minus `withdrawals_root`),

specs/capella/light-client/sync-protocol.md

@@ -14,6 +14,7 @@
 - [Containers](#containers)
   - [Modified `LightClientHeader`](#modified-lightclientheader)
 - [Helper functions](#helper-functions)
+  - [`execution_payload_gindex_at_slot`](#execution_payload_gindex_at_slot)
   - [`get_lc_execution_root`](#get_lc_execution_root)
   - [Modified `is_valid_light_client_header`](#modified-is_valid_light_client_header)
 
@@ -55,6 +56,16 @@ class LightClientHeader(Container):
 
 ## Helper functions
 
+### `execution_payload_gindex_at_slot`
+
+```python
+def execution_payload_gindex_at_slot(slot: Slot) -> GeneralizedIndex:
+    epoch = compute_epoch_at_slot(slot)
+    assert epoch >= CAPELLA_FORK_EPOCH
+
+    return EXECUTION_PAYLOAD_GINDEX
+```
+
 ### `get_lc_execution_root`
 
 ```python
@@ -79,11 +90,10 @@ def is_valid_light_client_header(header: LightClientHeader) -> bool:
             and header.execution_branch == ExecutionBranch()
         )
 
-    return is_valid_merkle_branch(
+    return is_valid_normalized_merkle_branch(
         leaf=get_lc_execution_root(header),
         branch=header.execution_branch,
-        depth=floorlog2(EXECUTION_PAYLOAD_GINDEX),
-        index=get_subtree_index(EXECUTION_PAYLOAD_GINDEX),
+        gindex=execution_payload_gindex_at_slot(header.beacon.slot),
         root=header.beacon.body_root,
     )
 ```

specs/deneb/light-client/full-node.md

@@ -53,7 +53,7 @@ def block_to_light_client_header(block: SignedBeaconBlock) -> LightClientHeader:
             execution_header.excess_blob_gas = payload.excess_blob_gas
 
         execution_branch = ExecutionBranch(
-            compute_merkle_proof(block.message.body, EXECUTION_PAYLOAD_GINDEX))
+            compute_merkle_proof(block.message.body, execution_payload_gindex_at_slot(block.message.slot)))
     else:
         # Note that during fork transitions, `finalized_header` may still point to earlier forks.
         # While Bellatrix blocks also contain an `ExecutionPayload` (minus `withdrawals_root`),

specs/deneb/light-client/sync-protocol.md

@@ -77,11 +77,10 @@ def is_valid_light_client_header(header: LightClientHeader) -> bool:
             and header.execution_branch == ExecutionBranch()
         )
 
-    return is_valid_merkle_branch(
+    return is_valid_normalized_merkle_branch(
         leaf=get_lc_execution_root(header),
         branch=header.execution_branch,
-        depth=floorlog2(EXECUTION_PAYLOAD_GINDEX),
-        index=get_subtree_index(EXECUTION_PAYLOAD_GINDEX),
+        gindex=execution_payload_gindex_at_slot(header.beacon.slot),
         root=header.beacon.body_root,
     )
 ```

specs/deneb/p2p-interface.md

@@ -14,6 +14,7 @@ The specification of these changes continues in the same format as the network s
   - [Constant](#constant)
   - [Preset](#preset)
   - [Configuration](#configuration)
+  - [Custom types](#custom-types)
   - [Containers](#containers)
     - [`BlobSidecar`](#blobsidecar)
     - [`BlobIdentifier`](#blobidentifier)
@@ -66,6 +67,12 @@ The specification of these changes continues in the same format as the network s
 | `MIN_EPOCHS_FOR_BLOB_SIDECARS_REQUESTS`  | `2**12` (= 4096 epochs, ~18 days) | The minimum epoch range over which a node must serve blob sidecars  |
 | `BLOB_SIDECAR_SUBNET_COUNT`              | `6`                               | The number of blob sidecar subnets used in the gossipsub protocol.  |
 
+### Custom types
+
+| Name | SSZ equivalent | Description |
+| - | - | - |
+| `KZGCommitmentInclusionProof` | `Vector[Bytes32, KZG_COMMITMENT_INCLUSION_PROOF_DEPTH]` | Merkle branch of a single `blob_kzg_commitments` list item within `BeaconBlockBody` |
+
 ### Containers
 
 #### `BlobSidecar`
@@ -79,7 +86,7 @@ class BlobSidecar(Container):
     kzg_commitment: KZGCommitment
     kzg_proof: KZGProof  # Allows for quick verification of kzg_commitment
     signed_block_header: SignedBeaconBlockHeader
-    kzg_commitment_inclusion_proof: Vector[Bytes32, KZG_COMMITMENT_INCLUSION_PROOF_DEPTH]
+    kzg_commitment_inclusion_proof: KZGCommitmentInclusionProof
 ```
 
 #### `BlobIdentifier`
@@ -98,12 +105,12 @@ class BlobIdentifier(Container):
 
 ```python
 def verify_blob_sidecar_inclusion_proof(blob_sidecar: BlobSidecar) -> bool:
-    gindex = get_subtree_index(get_generalized_index(BeaconBlockBody, 'blob_kzg_commitments', blob_sidecar.index))
+    gindex = get_generalized_index(BeaconBlockBody, 'blob_kzg_commitments', blob_sidecar.index)
     return is_valid_merkle_branch(
         leaf=blob_sidecar.kzg_commitment.hash_tree_root(),
         branch=blob_sidecar.kzg_commitment_inclusion_proof,
-        depth=KZG_COMMITMENT_INCLUSION_PROOF_DEPTH,
-        index=gindex,
+        depth=floorlog2(gindex),
+        index=get_subtree_index(gindex),
         root=blob_sidecar.signed_block_header.message.body_root,
     )
 ```