diff --git a/da/api/__init__.py b/da/api/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/da/api/common.py b/da/api/common.py
new file mode 100644
index 0000000..0d8afc9
--- /dev/null
+++ b/da/api/common.py
@@ -0,0 +1,50 @@
+from abc import ABC, abstractmethod
+from dataclasses import dataclass
+from typing import Optional, List, Sequence
+
+from da.common import Certificate
+from da.verifier import DABlob
+
+
+@dataclass
+class Metadata:
+    # index of VID certificate blob
+    index: int
+    # app identifier
+    app_id: bytes
+
+
+class BlobStore(ABC):
+    @abstractmethod
+    def add(self, certificate: Certificate, metadata: Metadata):
+        """
+        Raises: ValueError if there is already a registered certificate fot the given metadata
+        """
+        pass
+
+    @abstractmethod
+    def get_multiple(self, app_id: bytes, indexes: Sequence[int]) -> List[Optional[DABlob]]:
+        pass
+
+
+class DAApi:
+    def __init__(self, bs: BlobStore):
+        self.store = bs
+
+    def write(self, certificate: Certificate, metadata: Metadata):
+        """
+        Write method should be used by a service that is able to retrieve verified certificates
+        from the latest Block. Once a certificate is retrieved, api creates a relation between
+        the blob of an original data, certificate and index for the app_id of the certificate.
+        Raises: ValueError if there is already a registered certificate for a given metadata
+        """
+        self.store.add(certificate, metadata)
+
+    def read(self, app_id, indexes) -> List[Optional[DABlob]]:
+        """
+        Read method should accept only `app_id` and a list of indexes. The returned list of
+        blobs should be ordered in the same sequence as `indexes` in a request.
+        If node does not have the blob for some indexes, then it should add None object as an
+        item.
+        """
+        return self.store.get_multiple(app_id, indexes)
diff --git a/da/api/test_flow.py b/da/api/test_flow.py
new file mode 100644
index 0000000..bf88fc1
--- /dev/null
+++ b/da/api/test_flow.py
@@ -0,0 +1,72 @@
+from unittest import TestCase
+from collections import defaultdict
+
+from da.api.common import *
+
+
+@dataclass
+class MockCertificate:
+    cert_id: int
+
+
+class MockStore(BlobStore):
+    def __init__(self):
+        self.blob_store = {}
+        self.app_id_store = defaultdict(dict)
+
+    def populate(self, blob, cert_id: bytes):
+        self.blob_store[cert_id] = blob
+
+    # Implements `add` method from BlobStore abstract class.
+    def add(self, cert_id: bytes, metadata: Metadata):
+        if metadata.index in self.app_id_store[metadata.app_id]:
+            raise ValueError("index already written")
+
+        blob = self.blob_store.pop(cert_id)
+        self.app_id_store[metadata.app_id][metadata.index] = blob 
+
+    # Implements `get_multiple` method from BlobStore abstract class.
+    def get_multiple(self, app_id, indexes) -> List[Optional[DABlob]]:
+        return [
+                self.app_id_store[app_id].get(i) for i in indexes
+        ]
+
+
+class TestFlow(TestCase):
+    def test_api_write_read(self):
+        expected_blob = "hello"
+        cert_id = b"11"*32
+        app_id = 1
+        idx = 1
+        mock_meta = Metadata(1, 1)
+
+        mock_store = MockStore()
+        mock_store.populate(expected_blob, cert_id)
+
+        api = DAApi(mock_store)
+
+        api.write(cert_id, mock_meta)
+        blobs = api.read(app_id, [idx])
+
+        self.assertEqual([expected_blob], blobs)
+
+    def test_same_index(self):
+        expected_blob = "hello"
+        cert_id = b"11"*32
+        app_id = 1
+        idx = 1
+        mock_meta = Metadata(1, 1)
+
+        mock_store = MockStore()
+        mock_store.populate(expected_blob, cert_id)
+
+        api = DAApi(mock_store)
+
+        api.write(cert_id, mock_meta)
+        with self.assertRaises(ValueError):
+            api.write(cert_id, mock_meta)
+
+        blobs = api.read(app_id, [idx])
+
+        self.assertEqual([expected_blob], blobs)
+