Rename `recover_cells` to `recover_polynomial` and fix function signature. Add basic test case.

presets/mainnet/peerdas.yaml

@@ -0,0 +1,6 @@
+# Mainnet preset - PeerDAS
+
+# Misc
+# ---------------------------------------------------------------
+# `uint64(2**6)` (= 64)
+FIELD_ELEMENTS_PER_CELL: 64

presets/minimal/peerdas.yaml

@@ -0,0 +1,6 @@
+# Minimal preset - PeerDAS
+
+# Misc
+# ---------------------------------------------------------------
+# `uint64(2**6)` (= 64)
+FIELD_ELEMENTS_PER_CELL: 64

pysetup/spec_builders/peerdas.py

@@ -12,3 +12,9 @@ class PeerDASSpecBuilder(BaseSpecBuilder):
         return f'''
 from eth2spec.deneb import {preset_name} as deneb
 '''
+
+    @classmethod
+    def hardcoded_custom_type_dep_constants(cls, spec_object) -> Dict[str, str]:
+        return {
+            'FIELD_ELEMENTS_PER_CELL': spec_object.preset_vars['FIELD_ELEMENTS_PER_CELL'].value,
+        }

specs/_features/peerdas/polynomial-commitments-sampling.md

@@ -42,7 +42,7 @@
     - [`verify_cell_proof`](#verify_cell_proof)
     - [`verify_cell_proof_batch`](#verify_cell_proof_batch)
 - [Reconstruction](#reconstruction)
-  - [`recover_cells`](#recover_cells)
+  - [`recover_polynomial`](#recover_polynomial)
 
 <!-- END doctoc generated TOC please keep comment here to allow auto update -->
 <!-- /TOC -->
@@ -60,6 +60,8 @@ Public functions MUST accept raw bytes as input and perform the required cryptog
 | Name | SSZ equivalent | Description |
 | - | - | - |
 | `PolynomialCoeff` | `Vector[BLSFieldElement, FIELD_ELEMENTS_PER_BLOB]` | A polynomial in coefficient form |
+| `Cell` | `Vector[BLSFieldElement, FIELD_ELEMENTS_PER_CELL]` | The unit of blob data that can come with their own KZG proofs |
+| `CellID` | `uint64` | Cell identifier |
 
 ## Constants
 
@@ -334,15 +336,13 @@ def verify_kzg_proof_multi_impl(commitment: KZGCommitment,
 #### `coset_for_cell`
 
 ```python
-def coset_for_cell(cell_id: int) -> Vector[BLSFieldElement, FIELD_ELEMENTS_PER_CELL]:
+def coset_for_cell(cell_id: int) -> Cell:
     """
     Get the coset for a given ``cell_id``
     """
     assert cell_id < CELLS_PER_BLOB
     roots_of_unity_brp = bit_reversal_permutation(ROOTS_OF_UNITY_EXTENDED)
-    return Vector[BLSFieldElement, FIELD_ELEMENTS_PER_CELL](
+    return Cell(roots_of_unity_brp[FIELD_ELEMENTS_PER_CELL * cell_id:FIELD_ELEMENTS_PER_CELL * (cell_id + 1)])
-        roots_of_unity_brp[FIELD_ELEMENTS_PER_CELL * cell_id:FIELD_ELEMENTS_PER_CELL * (cell_id + 1)]
-    )
 ```
 
 ## Cells
@@ -353,7 +353,7 @@ def coset_for_cell(cell_id: int) -> Vector[BLSFieldElement, FIELD_ELEMENTS_PER_C
 
 ```python
 def compute_cells_and_proofs(blob: Blob) -> Tuple[
-        Vector[Vector[BLSFieldElement, FIELD_ELEMENTS_PER_CELL], CELLS_PER_BLOB],
+        Vector[Cell, CELLS_PER_BLOB],
         Vector[KZGProof, CELLS_PER_BLOB]]:
     """
     Compute all the cell proofs for one blob. This is an inefficient O(n^2) algorithm,
@@ -380,7 +380,7 @@ def compute_cells_and_proofs(blob: Blob) -> Tuple[
 #### `compute_cells`
 
 ```python
-def compute_cells(blob: Blob) -> Vector[Vector[BLSFieldElement, FIELD_ELEMENTS_PER_CELL], CELLS_PER_BLOB]:
+def compute_cells(blob: Blob) -> Vector[Cell, CELLS_PER_BLOB]:
     """
     Compute the cell data for a blob (without computing the proofs).
 
@@ -402,7 +402,7 @@ def compute_cells(blob: Blob) -> Vector[Vector[BLSFieldElement, FIELD_ELEMENTS_P
 ```python
 def verify_cell_proof(commitment: KZGCommitment,
                       cell_id: int,
-                      data: Vector[BLSFieldElement, FIELD_ELEMENTS_PER_CELL],
+                      cell: Cell,
                       proof: KZGProof) -> bool:
     """
     Check a cell proof
@@ -411,7 +411,7 @@ def verify_cell_proof(commitment: KZGCommitment,
     """
     coset = coset_for_cell(cell_id)
 
-    return verify_kzg_proof_multi_impl(commitment, coset, data, proof)
+    return verify_kzg_proof_multi_impl(commitment, coset, cell, proof)
 ```
 
 #### `verify_cell_proof_batch`
@@ -420,7 +420,7 @@ def verify_cell_proof(commitment: KZGCommitment,
 def verify_cell_proof_batch(row_commitments: Sequence[KZGCommitment],
                             row_ids: Sequence[int],
                             column_ids: Sequence[int],
-                            datas: Sequence[Vector[BLSFieldElement, FIELD_ELEMENTS_PER_CELL]],
+                            cells: Sequence[Cell],
                             proofs: Sequence[KZGProof]) -> bool:
     """
     Check multiple cell proofs. This function implements the naive algorithm of checking every cell
@@ -433,16 +433,18 @@ def verify_cell_proof_batch(row_commitments: Sequence[KZGCommitment],
     # Get commitments via row IDs
     commitments = [row_commitments[row_id] for row_id in row_ids]
     
-    return all(verify_kzg_proof_multi_impl(commitment, coset_for_cell(column_id), data, proof) 
+    return all(
-               for commitment, column_id, data, proof in zip(commitments, column_ids, datas, proofs))
+        verify_kzg_proof_multi_impl(commitment, coset_for_cell(column_id), cell, proof)
+        for commitment, column_id, cell, proof in zip(commitments, column_ids, cells, proofs)
+    )
 ```
 
 ## Reconstruction
 
-### `recover_cells`
+### `recover_polynomial`
 
 ```python
-def recover_cells(cells: Sequence[Tuple[int, ByteVector[BYTES_PER_CELL]]]) -> Polynomial:
+def recover_polynomial(cell_ids: Sequence[CellID], cells: Sequence[Cell]) -> Polynomial:
     """
     Recovers a polynomial from 2 * FIELD_ELEMENTS_PER_CELL evaluations, half of which can be missing.
 
@@ -452,8 +454,8 @@ def recover_cells(cells: Sequence[Tuple[int, ByteVector[BYTES_PER_CELL]]]) -> Po
 
     Public method.
     """
+    assert len(cell_ids) == len(cells)
     assert len(cells) >= CELLS_PER_BLOB // 2
-    cell_ids = [cell_id for cell_id, _ in cells]
     missing_cell_ids = [cell_id for cell_id in range(CELLS_PER_BLOB) if cell_id not in cell_ids]
     short_zero_poly = vanishing_polynomialcoeff([
         ROOTS_OF_UNITY_REDUCED[reverse_bits(cell_id, CELLS_PER_BLOB)]
@@ -477,10 +479,11 @@ def recover_cells(cells: Sequence[Tuple[int, ByteVector[BYTES_PER_CELL]]]) -> Po
         end = (cell_id + 1) * FIELD_ELEMENTS_PER_CELL
         assert all(a != 0 for a in zero_poly_eval_brp[start:end])
 
-    extended_evaluation_rbo = [0] * FIELD_ELEMENTS_PER_BLOB * 2
+    extended_evaluation_rbo = [0] * (FIELD_ELEMENTS_PER_BLOB * 2)
-    for cell_id, cell_data in cells:
+    for cell_id, cell in zip(cell_ids, cells):
-        extended_evaluation_rbo[cell_id * FIELD_ELEMENTS_PER_CELL:(cell_id + 1) * FIELD_ELEMENTS_PER_CELL] = \
+        start = cell_id * FIELD_ELEMENTS_PER_CELL
-            cell_data
+        end = (cell_id + 1) * FIELD_ELEMENTS_PER_CELL
+        extended_evaluation_rbo[start:end] = cell
     extended_evaluation = bit_reversal_permutation(extended_evaluation_rbo)
 
     extended_evaluation_times_zero = [a * b % BLS_MODULUS for a, b in zip(zero_poly_eval, extended_evaluation)]
@@ -507,9 +510,10 @@ def recover_cells(cells: Sequence[Tuple[int, ByteVector[BYTES_PER_CELL]]]) -> Po
 
     reconstructed_data = bit_reversal_permutation(fft_field(reconstructed_poly, ROOTS_OF_UNITY_EXTENDED))
 
-    for cell_id, cell_data in cells:
+    for cell_id, cell in zip(cell_ids, cells):
-        assert reconstructed_data[cell_id * FIELD_ELEMENTS_PER_CELL:(cell_id + 1) * FIELD_ELEMENTS_PER_CELL] == \
+        start = cell_id * FIELD_ELEMENTS_PER_CELL
-            cell_data
+        end = (cell_id + 1) * FIELD_ELEMENTS_PER_CELL
-    
+        assert reconstructed_data[start:end] == cell
+
     return reconstructed_data
 ```

specs/deneb/polynomial-commitments.md

@@ -602,4 +602,3 @@ def verify_blob_kzg_proof_batch(blobs: Sequence[Blob],
 
     return verify_kzg_proof_batch(commitments, evaluation_challenges, ys, proofs)
 ```
-

tests/core/pyspec/eth2spec/test/peerdas/unittests/polynomial_commitments/test_polynomial_commitments.py

@@ -41,9 +41,23 @@ def test_verify_cell_proof_batch(spec):
     cells, proofs = spec.compute_cells_and_proofs(blob)
 
     assert spec.verify_cell_proof_batch(
-        row_commitments = [commitment],
+        row_commitments=[commitment],
-        row_ids = [0],
+        row_ids=[0],
-        column_ids = [0, 1],
+        column_ids=[0, 1],
-        datas = [cells[0], cells[1]],
+        cells=cells[0:1],
-        proofs = proofs,
+        proofs=proofs,
     )
+
+
+@with_peerdas_and_later
+@spec_test
+@single_phase
+def test_recover_polynomial(spec):
+    blob = get_sample_blob(spec)
+    original_polynomial = spec.blob_to_polynomial(blob)
+    cells = spec.compute_cells(blob)
+    cell_ids = list(range(spec.CELLS_PER_BLOB // 2))
+    known_cells = [cells[cell_id] for cell_id in cell_ids]
+    result = spec.recover_polynomial(cell_ids, known_cells)
+
+    assert original_polynomial == result[0:len(result) // 2]