Add HistoricalRootsBlockProof for merge till capella blocks

history-network.md

@@ -160,13 +160,25 @@ each receipt/transaction and re-rlp-encode it, but only if it is a legacy transa
 
 #### Block Header
 
-
 ```
 # Content types
 
 AccumulatorProof = Vector[Bytes32, 15]
 
-BlockHeaderProof = Union[None, AccumulatorProof]
+BeaconBlockBodyProof = Vector[Bytes32, 8] # Proof that EL block_hash in ExecutionPayload is part of BeaconBlockBody
+BeaconBlockHeaderProof = Vector[Bytes32, 3] # Proof that BeaconBlockBody root is part of BeaconBlockHeader
+HistoricalRootsProof = Vector[Bytes32, 14] # Proof that BeaconBlockHeader root is part of HistoricalRoots
+
+HistoricalRootsBlockProof = Container[
+    beaconBlockBodyProof: BeaconBlockBodyProof,
+    beaconBlockBodyRoot: Bytes32,
+    beaconBlockHeaderProof: BeaconBlockHeaderProof,
+    beaconBlockHeaderRoot: Bytes32,
+    historicalRootsProof: HistoricalRootsProof,
+    slot: Slot
+]
+
+BlockHeaderProof = Union[None, AccumulatorProof, HistoricalRootsBlockProof]
 
 BlockHeaderWithProof = Container[
   header: ByteList, # RLP encoded header in SSZ ByteList
@@ -333,5 +345,14 @@ Merkle proof with the `BlockHeader`'s block hash as leave and the
 `EpochAccumulator` digest as root. This digest is available in the
 `MasterAccumulator`.
 
-As the `MasterAccumulator` only accounts for blocks pre-merge, this proof can
-only be used to verify blocks pre-merge.
+As the `MasterAccumulator` 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 three 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 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 The Merge 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 so choose.