From 9274a661993d315a40f0e5ec3b3cac3a80e78825 Mon Sep 17 00:00:00 2001
From: Potuz <potuz@prysmaticlabs.com>
Date: Mon, 8 Jul 2024 13:32:33 -0300
Subject: [PATCH] fix Merkle proof generator

---
 presets/mainnet/eip-7732.yaml            |  1 -
 presets/minimal/eip-7732.yaml            |  1 -
 pysetup/spec_builders/eip7732.py         | 12 ++++++++++--
 specs/_features/eip7732/builder.md       |  8 ++++----
 specs/_features/eip7732/p2p-interface.md | 14 +++++++++++---
 5 files changed, 25 insertions(+), 11 deletions(-)

diff --git a/presets/mainnet/eip-7732.yaml b/presets/mainnet/eip-7732.yaml
index eca2dd705..eb43c981a 100644
--- a/presets/mainnet/eip-7732.yaml
+++ b/presets/mainnet/eip-7732.yaml
@@ -7,4 +7,3 @@ PTC_SIZE: 512
 # 2**2 (= 4)
 MAX_PAYLOAD_ATTESTATIONS: 4
 KZG_COMMITMENT_INCLUSION_PROOF_DEPTH_EIP7732: 13
-KZG_GENERALIZED_INDEX_PREFIX: 486
diff --git a/presets/minimal/eip-7732.yaml b/presets/minimal/eip-7732.yaml
index efbfdfad9..751c1325a 100644
--- a/presets/minimal/eip-7732.yaml
+++ b/presets/minimal/eip-7732.yaml
@@ -7,4 +7,3 @@ PTC_SIZE: 2
 # 2**2 (= 4)
 MAX_PAYLOAD_ATTESTATIONS: 4
 KZG_COMMITMENT_INCLUSION_PROOF_DEPTH_EIP7732: 13
-KZG_GENERALIZED_INDEX_PREFIX: 486
diff --git a/pysetup/spec_builders/eip7732.py b/pysetup/spec_builders/eip7732.py
index 2117f9633..0c335fe1d 100644
--- a/pysetup/spec_builders/eip7732.py
+++ b/pysetup/spec_builders/eip7732.py
@@ -13,6 +13,16 @@ class EIP7732SpecBuilder(BaseSpecBuilder):
 from eth2spec.electra import {preset_name} as electra
 '''
 
+    @classmethod
+    def sundry_functions(cls) -> str:
+        return '''
+def concat_generalized_indices(*indices: GeneralizedIndex) -> GeneralizedIndex:
+    o = GeneralizedIndex(1)
+    for i in indices:
+        o = GeneralizedIndex(o * bit_floor(i) + (i - bit_floor(i)))
+    return o'''
+
+
     @classmethod
     def hardcoded_custom_type_dep_constants(cls, spec_object) -> Dict[str, str]:
         return {
@@ -20,8 +30,6 @@ from eth2spec.electra import {preset_name} as electra
             'MAX_PAYLOAD_ATTESTATIONS': spec_object.preset_vars['MAX_PAYLOAD_ATTESTATIONS'].value,
             'KZG_COMMITMENT_INCLUSION_PROOF_DEPTH_EIP7732':
                 spec_object.preset_vars['KZG_COMMITMENT_INCLUSION_PROOF_DEPTH_EIP7732'].value,
-            'KZG_GENERALIZED_INDEX_PREFIX':
-                spec_object.preset_vars['KZG_GENERALIZED_INDEX_PREFIX'].value,
         }
 
     @classmethod
diff --git a/specs/_features/eip7732/builder.md b/specs/_features/eip7732/builder.md
index 9d28e2e6c..491f625d8 100644
--- a/specs/_features/eip7732/builder.md
+++ b/specs/_features/eip7732/builder.md
@@ -73,6 +73,10 @@ def get_blob_sidecars(signed_block: SignedBeaconBlock,
     sidecars: List[BlobSidecar] = []
     for index, blob in enumerate(blobs):
         proof = compute_merkle_proof(
+            blob_kzg_commitments,
+            get_generalized_index(List[KZGCommitment, MAX_BLOB_COMMITMENTS_PER_BLOCK], index),
+        )
+        proof += compute_merkle_proof(
             block.body,
             get_generalized_index(
                 BeaconBlockBody,
@@ -81,10 +85,6 @@ def get_blob_sidecars(signed_block: SignedBeaconBlock,
                 "blob_kzg_commitments_root",
             ),
         )
-        proof += compute_merkle_proof(
-            blob_kzg_commitments,
-            get_generalized_index(List[KZGCommitment, MAX_BLOB_COMMITMENTS_PER_BLOCK], index),
-        )
         sidecars.append(
             BlobSidecar(
                 index=index,
diff --git a/specs/_features/eip7732/p2p-interface.md b/specs/_features/eip7732/p2p-interface.md
index dd4e7a827..52546070f 100644
--- a/specs/_features/eip7732/p2p-interface.md
+++ b/specs/_features/eip7732/p2p-interface.md
@@ -36,7 +36,6 @@ This document contains the consensus-layer networking specification for EIP7732.
 | Name                                     | Value                             | Description                                                         |
 |------------------------------------------|-----------------------------------|---------------------------------------------------------------------|
 | `KZG_COMMITMENT_INCLUSION_PROOF_DEPTH_EIP7732`   | `13` # TODO: Compute it when the spec stabilizes | Merkle proof depth for the `blob_kzg_commitments` list item |
-| `KZG_GENERALIZED_INDEX_PREFIX`           | `486` # TODO: Compute it when the spec stabilizes | Generalized index for the first item in the `blob_kzg_commitments` list |
 
 
 ### Containers
@@ -63,8 +62,17 @@ class BlobSidecar(Container):
 
 ```python
 def verify_blob_sidecar_inclusion_proof(blob_sidecar: BlobSidecar) -> bool:
-    # hardcoded here because the block does not include the commitments but only their root. 
-    gindex = GeneralizedIndex(KZG_GENERALIZED_INDEX_PREFIX + blob_sidecar.index)
+    inner_gindex = get_generalized_index(
+        List[KZGCommitment, MAX_BLOB_COMMITMENTS_PER_BLOCK],
+        blob_sidecar.index
+    )
+    outer_gindex = get_generalized_index(
+        BeaconBlockBody,
+        "signed_execution_payload_header",
+        "message",
+        "blob_kzg_commitments_root",
+    )
+    gindex = get_subtree_index(concat_generalized_indices(outer_gindex, inner_gindex))
 
     return is_valid_merkle_branch(
         leaf=blob_sidecar.kzg_commitment.hash_tree_root(),