diff --git a/da/common.py b/da/common.py
new file mode 100644
index 0000000..507e6b5
--- /dev/null
+++ b/da/common.py
@@ -0,0 +1,31 @@
+from dataclasses import dataclass
+from typing import List
+
+from eth2spec.eip7594.mainnet import Bytes32
+
+
+class Chunk(Bytes32):
+    pass
+
+
+class Column(List[Chunk]):
+    pass
+
+
+class Row(List[Chunk]):
+    pass
+
+
+class ChunksMatrix(List[Row]):
+    pass
+
+
+@dataclass
+class Attestation:
+    pass
+
+
+@dataclass
+class Certificate:
+    pass
+
diff --git a/da/dispersal.py b/da/dispersal.py
index b9cfd67..9c71751 100644
--- a/da/dispersal.py
+++ b/da/dispersal.py
@@ -1,14 +1,11 @@
 from typing import List, Optional, Generator
 
+from da.common import Certificate
 from da.encoder import EncodedData
 from da.verifier import DABlob, Attestation
 from mixnet.node import NodeId
 
 
-class Certificate:
-    pass
-
-
 class Dispersal:
     def __init__(self, nodes: List[NodeId], threshold: int):
         self.nodes = nodes
diff --git a/da/encoder.py b/da/encoder.py
index fe32245..97380e9 100644
--- a/da/encoder.py
+++ b/da/encoder.py
@@ -2,9 +2,7 @@ from dataclasses import dataclass
 from typing import List
 from eth2spec.eip7594.mainnet import KZGCommitment as Commitment, KZGProof as Proof
 
-
-class ChunksMatrix(List[bytearray]):
-    pass
+from da.common import ChunksMatrix
 
 
 @dataclass
diff --git a/da/verifier.py b/da/verifier.py
index 58ad5ea..12f9727 100644
--- a/da/verifier.py
+++ b/da/verifier.py
@@ -7,6 +7,8 @@ from eth2spec.eip7594.mainnet import (
 )
 from itertools import batched
 
+from da.common import Column, Chunk, Attestation
+
 
 @dataclass
 class DABlob:
@@ -20,18 +22,13 @@ class DABlob:
     rows_proofs: List[Proof]
 
 
-@dataclass
-class Attestation:
-    pass
-
-
 class DAVerifier:
     def __init__(self):
         pass
 
     @staticmethod
     def _verify_column(
-            column: bytearray,
+            column: Column,
             column_commitment: Commitment,
             aggregated_column_commitment: Commitment,
             aggregated_column_proof: Proof,
@@ -44,15 +41,15 @@ class DAVerifier:
         # 3. compute column hash
         column_hash: bytearray = bytearray(hash(column))
         # 4. Check proof with commitment and proof over the aggregated column commitment
-        pass
+        return False
 
     @staticmethod
-    def _verify_chunk(chunk: bytearray, commitment: Commitment, proof: Proof) -> bool:
+    def _verify_chunk(chunk: Chunk, commitment: Commitment, proof: Proof) -> bool:
         pass
 
     @staticmethod
     def _verify_chunks(
-            chunks: List[bytearray],
+            chunks: List[Chunk],
             commitments: List[Commitment],
             proofs: List[Proof]
     ) -> bool: