Add HistoricalRootsBlockProof for merge till capella blocks

history/history-network.md

@@ -155,9 +155,25 @@ each receipt/transaction and re-rlp-encode it, but only if it is a legacy transa
 ```python
 # Content types
 
+# Proof for EL BlockHeader before TheMerge / Paris
 HistoricalHashesAccumulatorProof = Vector[Bytes32, 15]
 
-BlockHeaderProof = Union[None, HistoricalHashesAccumulatorProof]
+# Proof that EL block_hash is in  BeaconBlock -> BeaconBlockBody -> ExecutionPayload
+BeaconBlockProof = Vector[Bytes32, 11]
+
+# Proof that BeaconBlock root is part of HistoricalRoots and thus canonical
+# For after TheMerge until Capella -> Bellatrix fork.
+HistoricalRootsProof = Vector[Bytes32, 14]
+
+# Proof for EL BlockHeader after TheMerge until Capella
+HistoricalRootsBlockProof = Container[
+    beaconBlockProof: BeaconBlockProof,
+    beaconBlocRoot: Bytes32,
+    historicalRootsProof: HistoricalRootsProof,
+    slot: Slot
+]
+
+BlockHeaderProof = Union[None, HistoricalHashesAccumulatorProof, HistoricalRootsBlockProof]
 
 BlockHeaderWithProof = Container(
   header: ByteList[MAX_HEADER_LENGTH], # RLP encoded header in SSZ ByteList
@@ -168,7 +184,9 @@ BlockHeaderWithProof = Container(
 > **_Note:_** The `BlockHeaderProof` allows to provide headers without a proof (`None`).
 For pre-merge headers, clients SHOULD NOT accept headers without a proof
 as there is the `HistoricalHashesAccumulatorProof` solution available.
-For post-merge headers, there is currently no proof solution and clients MAY
+For post-merge until Capella headers, clients SHOULD NOT accept headers without a proof as there is the `HistoricalRootsBlockProof` solution available.
+
+For post Capella headers, there is currently no proof solution and clients SHOULD
 accept headers without a proof.
 
 ##### Block Header by Hash
@@ -347,5 +365,13 @@ Merkle proof with the `BlockHeader`'s block hash as leave and the
 `EpochRecord` digest as root. This digest is available in the
 `HistoricalHashesAccumulator`.
 
-As the `HistoricalHashesAccumulator` only accounts for blocks pre-merge, this proof can
-only be used to verify blocks pre-merge.
+As the `HistoricalHashesAccumulator` only accounts for blocks pre-merge, this proof MUST be used to verify blocks pre-merge (pre Paris fork).
+
+#### HistoricalRootsBlockProof
+
+The `HistoricalRootsBlockProof` is an SSZ container which holds two Merkle proofs as specified in the [SSZ Merke proofs specification](https://github.com/ethereum/consensus-specs/blob/dev/ssz/merkle-proofs.md#merkle-multiproofs).
+
+The container holds a chain of 2 proofs. This chain of proofs allows for verifying that an EL `BlockHeader` is part of the canonical chain. The only requirement is having access to the beacon chain `historical_roots`.
+The `historical_roots` is a [`BeaconState` field](https://github.com/ethereum/consensus-specs/blob/dev/specs/capella/beacon-chain.md#beaconstate) that is frozen since the Capella fork. The `HistoricalRootsBlockProof` MUST be used to verify blocks from TheMerge/Paris until the Capella fork.
+
+The Portal network does not provide a mechanism to acquire the `historical_roots` over the network. Clients are encouraged to solve this however they choose, with the suggestion that they can include a frozen copy of the `historical_roots` within their client code, and provide a mechanism for users to override this value if they choose so.