feat(cardano): add support for chunked embedded CBOR

core/src/apps/cardano/helpers/hash_builder_collection.py

@@ -120,3 +120,20 @@ class HashBuilderDict(HashBuilderCollection, Generic[K, V]):
 
     def _header_bytes(self) -> bytes:
         return cbor.create_map_header(self.size)
+
+
+class HashBuilderEmbeddedCBOR(HashBuilderCollection):
+    """
+    Accepts data chunks and serializes them as embedded CBOR.
+    Note that self.remaining holds the remaining data size in bytes (not chunks).
+    Child HashBuilders are not allowed.
+    """
+
+    def add(self, chunk: bytes) -> None:
+        assert self.hash_fn is not None
+        assert self.remaining >= len(chunk)
+        self.remaining -= len(chunk)
+        self.hash_fn.update(chunk)
+
+    def _header_bytes(self) -> bytes:
+        return cbor.create_embedded_cbor_bytes_header(self.size)

core/src/apps/common/cbor.py

@@ -320,6 +320,14 @@ def create_map_header(size: int) -> bytes:
     return _header(_CBOR_MAP, size)
 
 
+def create_embedded_cbor_bytes_header(size: int) -> bytes:
+    """
+    Bytes wrapped in Tag 24 (embedded CBOR).
+    https://datatracker.ietf.org/doc/html/rfc7049#section-2.4.4.1
+    """
+    return _header(_CBOR_TAG, _CBOR_RAW_TAG) + _header(_CBOR_BYTE_STRING, size)
+
+
 def precedes(prev: bytes, curr: bytes) -> bool:
     """
     Returns True if `prev` is smaller than `curr` with regards to

core/tests/test_apps.common.cbor.py

@@ -8,6 +8,7 @@ from apps.common.cbor import (
     Tagged,
     create_array_header,
     create_map_header,
+    create_embedded_cbor_bytes_header,
     decode,
     encode,
     encode_chunked,
@@ -48,6 +49,22 @@ class TestCardanoCbor(unittest.TestCase):
         with self.assertRaises(NotImplementedError):
             create_map_header(2 ** 64)
 
+    def test_create_embedded_cbor_bytes_header(self):
+        test_vectors = [
+            (0, 'd81840'),
+            (23, 'd81857'),
+            ((2 ** 8) - 1, 'd81858ff'),
+            ((2 ** 16) - 1, 'd81859ffff'),
+            ((2 ** 32) - 1, 'd8185affffffff'),
+            ((2 ** 64) - 1, 'd8185bffffffffffffffff'),
+        ]
+        for val, header_hex in test_vectors:
+            header = unhexlify(header_hex)
+            self.assertEqual(create_embedded_cbor_bytes_header(val), header)
+
+        with self.assertRaises(NotImplementedError):
+            create_embedded_cbor_bytes_header(2 ** 64)
+
     def test_cbor_encoding(self):
         test_vectors = [
             # unsigned integers