Threshold bitfield on certificate (#81)

* Added threshold bitfield to certificate

* Short nodes_ids and public_keys

da/common.py

@@ -39,6 +39,10 @@ BLSPrivateKey = int
 BLSSignature = bytes
 
 
+class Bitfield(List[bool]):
+    pass
+
+
 @dataclass
 class Attestation:
     signature: BLSSignature
@@ -47,6 +51,7 @@ class Attestation:
 @dataclass
 class Certificate:
     aggregated_signatures: BLSSignature
+    signers: Bitfield
     aggregated_column_commitment: Commitment
     row_commitments: List[Commitment]
 

da/dispersal.py

@@ -4,7 +4,7 @@ from typing import List, Optional, Generator, Sequence
 
 from py_ecc.bls import G2ProofOfPossession as bls_pop
 
-from da.common import Certificate, NodeId, BLSPublickey
+from da.common import Certificate, NodeId, BLSPublickey, Bitfield
 from da.encoder import EncodedData
 from da.verifier import DABlob, Attestation
 
@@ -19,6 +19,10 @@ class DispersalSettings:
 class Dispersal:
     def __init__(self, settings: DispersalSettings):
         self.settings = settings
+        # sort nodes_ids and related public keys
+        self.settings.nodes_ids, self.settings.nodes_pubkey = zip(
+            *sorted(zip(self.settings.nodes_ids, self.settings.nodes_pubkey), key=lambda x: x[0])
+        )
 
     def _prepare_data(self, encoded_data: EncodedData) -> Generator[DABlob, None, None]:
         assert len(encoded_data.column_commitments) == len(self.settings.nodes_ids)
@@ -45,11 +49,18 @@ class Dispersal:
     def _send_and_await_response(self, node: NodeId, blob: DABlob) -> Optional[Attestation]:
         pass
 
-    def _build_certificate(self, encoded_data: EncodedData, attestations: Sequence[Attestation]) -> Certificate:
+    def _build_certificate(
+            self,
+            encoded_data: EncodedData,
+            attestations: Sequence[Attestation],
+            signers: Bitfield
+    ) -> Certificate:
         assert len(attestations) >= self.settings.threshold
+        assert len(attestations) == signers.count(True)
         aggregated = bls_pop.Aggregate([attestation.signature for attestation in attestations])
         return Certificate(
             aggregated_signatures=aggregated,
+            signers=signers,
             aggregated_column_commitment=encoded_data.aggregated_column_commitment,
             row_commitments=encoded_data.row_commitments
         )
@@ -69,9 +80,18 @@ class Dispersal:
     def disperse(self, encoded_data: EncodedData) -> Optional[Certificate]:
         attestations = []
         attested_message = self._build_attestation_message(encoded_data)
-        for node, pk, blob in zip(self.settings.nodes_ids, self.settings.nodes_pubkey,  self._prepare_data(encoded_data)):
+        signed = Bitfield(False for _ in range(len(self.settings.nodes_ids)))
+        blob_data = zip(
+            range(len(self.settings.nodes_ids)),
+            self.settings.nodes_ids,
+            self.settings.nodes_pubkey,
+            self._prepare_data(encoded_data)
+        )
+        for i, node, pk, blob in blob_data:
             if attestation := self._send_and_await_response(node, blob):
                 if self._verify_attestation(pk, attested_message, attestation):
+                    # mark as received
+                    signed[i] = True
                     attestations.append(attestation)
             if len(attestations) >= self.settings.threshold:
-                return self._build_certificate(encoded_data, attestations)
+                return self._build_certificate(encoded_data, attestations, signed)

da/test_dispersal.py

@@ -4,7 +4,7 @@ from unittest import TestCase
 from .encoder import DAEncoderParams, DAEncoder
 from .test_encoder import TestEncoder
 
-from da.common import NodeId, Attestation
+from da.common import NodeId, Attestation, Bitfield
 from da.dispersal import Dispersal, EncodedData, DispersalSettings
 from py_ecc.bls import G2ProofOfPossession as bls_pop
 
@@ -28,7 +28,7 @@ class TestDispersal(TestCase):
 
     def test_build_certificate_insufficient_attestations(self):
         with self.assertRaises(AssertionError):
-            self.dispersal._build_certificate(None, [])
+            self.dispersal._build_certificate(None, [], [])
 
     def test_build_certificate_enough_attestations(self):
         mock_encoded_data = EncodedData(
@@ -36,7 +36,11 @@ class TestDispersal(TestCase):
         )
         mock_message = sha3_256(mock_encoded_data.aggregated_column_commitment).digest()
         mock_attestations = [Attestation(bls_pop.Sign(sk, mock_message)) for sk in self.secret_keys]
-        certificate = self.dispersal._build_certificate(mock_encoded_data, mock_attestations)
+        certificate = self.dispersal._build_certificate(
+            mock_encoded_data,
+            mock_attestations,
+            Bitfield([True for _ in range(len(self.secret_keys))])
+        )
         self.assertIsNotNone(certificate)
         self.assertEqual(certificate.aggregated_column_commitment, mock_encoded_data.aggregated_column_commitment)
         self.assertEqual(certificate.row_commitments, [])
@@ -67,4 +71,8 @@ class TestDispersal(TestCase):
                 certificate.aggregated_signatures
             )
         )
+        self.assertEqual(
+            certificate.signers,
+            [True if i < self.dispersal.settings.threshold else False for i in range(self.n_nodes)]
+        )