diff --git a/suit_generator/cmd_convert.py b/suit_generator/cmd_convert.py
index 144a5ff4..27415e2f 100644
--- a/suit_generator/cmd_convert.py
+++ b/suit_generator/cmd_convert.py
@@ -93,6 +93,8 @@ def add_arguments(parser):
 class KeyConverter:
     """Creates a C file with public key data in form of an array from a private key stored in PEM format."""
 
+    DEFAULT_ENCODING = "utf-8"
+
     default_array_type = "uint8_t"
     default_array_name = "key_buf"
     default_length_type = "size_t"
@@ -187,7 +189,7 @@ def _validate_input_file(self):
 
     def _prepare_header(self) -> str:
         if self._header_file:
-            with open(self._header_file, "r") as fd:
+            with open(self._header_file, "r", encoding=self.DEFAULT_ENCODING) as fd:
                 contents = fd.read()
             if len(contents) > 0:
                 contents += KeyConverter.newline * 2
@@ -236,7 +238,7 @@ def _prepare_length_variable(self) -> str:
 
     def _prepare_footer(self) -> str:
         if self._footer_file:
-            with open(self._footer_file, "r") as fd:
+            with open(self._footer_file, "r", encoding=self.DEFAULT_ENCODING) as fd:
                 contents = fd.read()
             if len(contents) > 0:
                 contents = KeyConverter.newline + contents
@@ -300,7 +302,7 @@ def prepare_file_contents(self):
 
     def generate_c_file(self):
         """Create a C file containing public key data stored as an array."""
-        with open(self._output_file, "w") as fd:
+        with open(self._output_file, "w", encoding=self.DEFAULT_ENCODING) as fd:
             fd.write(self.prepare_file_contents())
 
 
diff --git a/suit_generator/input_output.py b/suit_generator/input_output.py
index c6a2373a..93117271 100644
--- a/suit_generator/input_output.py
+++ b/suit_generator/input_output.py
@@ -40,10 +40,12 @@ class InputOutputMixin:
         "suit_simplified": "from_suit_file_simplified",
     }
 
+    DEFAULT_ENCODING = "utf-8"
+
     @classmethod
     def from_json_file(cls, file_name: str) -> dict:
         """Read json file and return dict."""
-        with open(file_name, "r") as fh:
+        with open(file_name, "r", encoding=cls.DEFAULT_ENCODING) as fh:
             data = json.load(fh)
         return data
 
@@ -61,13 +63,13 @@ def parse_json_submanifests(cls, data):
     @classmethod
     def to_json_file(cls, file_name: str, data: dict, parse_hierarchy: bool, *args) -> None:
         """Write dict content into json file."""
-        with open(file_name, "w") as fh:
+        with open(file_name, "w", encoding=cls.DEFAULT_ENCODING) as fh:
             json.dump(cls.parse_json_submanifests(data) if parse_hierarchy is True else data, fh, sort_keys=False)
 
     @classmethod
     def from_yaml_file(cls, file_name) -> dict:
         """Read yaml file and return dict."""
-        with open(file_name, "r") as fh:
+        with open(file_name, "r", encoding=cls.DEFAULT_ENCODING) as fh:
             data = yaml.load(fh, Loader=yaml.SafeLoader)
         return data
 
@@ -92,7 +94,7 @@ def parse_yaml_submanifests(cls, data):
     @classmethod
     def to_yaml_file(cls, file_name, data, parse_hierarchy: bool, *args) -> None:
         """Write dict content into yaml file."""
-        with open(file_name, "w") as fh:
+        with open(file_name, "w", encoding=cls.DEFAULT_ENCODING) as fh:
             yaml.dump(cls.parse_yaml_submanifests(data) if parse_hierarchy is True else data, fh, sort_keys=False)
 
     @classmethod
diff --git a/suit_generator/suit/types/common.py b/suit_generator/suit/types/common.py
index 47c8f008..8a4d0188 100644
--- a/suit_generator/suit/types/common.py
+++ b/suit_generator/suit/types/common.py
@@ -93,7 +93,7 @@ def __init__(self, value):
         setattr(self, self.__class__.__name__, value)
 
     @staticmethod
-    def decode_cbor_length(subtype: int, data, allow_indefinite: bool = False) -> int | None:
+    def decode_cbor_length(subtype: int, data: bytes, allow_indefinite: bool = False) -> int | None:
         """Decode cbor object length.
 
         https://github.com/agronholm/cbor2/blob/master/cbor2/_decoder.py#L258-L272
@@ -102,7 +102,7 @@ def decode_cbor_length(subtype: int, data, allow_indefinite: bool = False) -> in
             if subtype < 24:
                 return subtype
             elif subtype == 24:
-                return data[0][0]
+                return data[0]
             elif subtype == 25:
                 return cast(int, struct.unpack(">H", data[:2])[0])
             elif subtype == 26: