diff --git a/src/aleph/sdk/chains/common.py b/src/aleph/sdk/chains/common.py
index 9f6b45f4..3c7e634e 100644
--- a/src/aleph/sdk/chains/common.py
+++ b/src/aleph/sdk/chains/common.py
@@ -27,9 +27,9 @@ def get_verification_buffer(message: Dict) -> bytes:
     # Convert Enum values to strings
     return "\n".join(
         (
-            enum_as_str(message["chain"]),
+            enum_as_str(message["chain"]) or "",
             message["sender"],
-            enum_as_str(message["type"]),
+            enum_as_str(message["type"]) or "",
             message["item_hash"],
         )
     ).encode()
diff --git a/src/aleph/sdk/query/filters.py b/src/aleph/sdk/query/filters.py
index 17c4a8cd..4caee5f5 100644
--- a/src/aleph/sdk/query/filters.py
+++ b/src/aleph/sdk/query/filters.py
@@ -1,9 +1,24 @@
 from datetime import datetime
+from enum import Enum
 from typing import Dict, Iterable, Optional, Union
 
 from aleph_message.models import MessageType
 
-from ..utils import _date_field_to_timestamp, serialize_list
+from ..utils import _date_field_to_timestamp, enum_as_str, serialize_list
+
+
+class SortBy(str, Enum):
+    """Supported SortBy types"""
+
+    TIME = "time"
+    TX_TIME = "tx-time"
+
+
+class SortOrder(str, Enum):
+    """Supported SortOrder types"""
+
+    ASCENDING = "1"
+    DESCENDING = "-1"
 
 
 class MessageFilter:
@@ -20,6 +35,8 @@ class MessageFilter:
     :param chains: Filter by sender address chain
     :param start_date: Earliest date to fetch messages from
     :param end_date: Latest date to fetch messages from
+    :param sort_by: Sort by time or tx-time
+    :param sort_order: Sort by ascending or descending order
     """
 
     message_types: Optional[Iterable[MessageType]]
@@ -33,6 +50,8 @@ class MessageFilter:
     chains: Optional[Iterable[str]]
     start_date: Optional[Union[datetime, float]]
     end_date: Optional[Union[datetime, float]]
+    sort_by: Optional[SortBy]
+    sort_order: Optional[SortOrder]
 
     def __init__(
         self,
@@ -47,6 +66,8 @@ def __init__(
         chains: Optional[Iterable[str]] = None,
         start_date: Optional[Union[datetime, float]] = None,
         end_date: Optional[Union[datetime, float]] = None,
+        sort_by: Optional[SortBy] = None,
+        sort_order: Optional[SortOrder] = None,
     ):
         self.message_types = message_types
         self.content_types = content_types
@@ -59,6 +80,8 @@ def __init__(
         self.chains = chains
         self.start_date = start_date
         self.end_date = end_date
+        self.sort_by = sort_by
+        self.sort_order = sort_order
 
     def as_http_params(self) -> Dict[str, str]:
         """Convert the filters into a dict that can be used by an `aiohttp` client
@@ -66,7 +89,7 @@ def as_http_params(self) -> Dict[str, str]:
         """
 
         partial_result = {
-            "msgType": serialize_list(
+            "msgTypes": serialize_list(
                 [type.value for type in self.message_types]
                 if self.message_types
                 else None
@@ -81,6 +104,8 @@ def as_http_params(self) -> Dict[str, str]:
             "chains": serialize_list(self.chains),
             "startDate": _date_field_to_timestamp(self.start_date),
             "endDate": _date_field_to_timestamp(self.end_date),
+            "sortBy": enum_as_str(self.sort_by),
+            "sortOrder": enum_as_str(self.sort_order),
         }
 
         # Ensure all values are strings.
@@ -110,6 +135,8 @@ class PostFilter:
     chains: Optional[Iterable[str]]
     start_date: Optional[Union[datetime, float]]
     end_date: Optional[Union[datetime, float]]
+    sort_by: Optional[SortBy]
+    sort_order: Optional[SortOrder]
 
     def __init__(
         self,
@@ -122,6 +149,8 @@ def __init__(
         chains: Optional[Iterable[str]] = None,
         start_date: Optional[Union[datetime, float]] = None,
         end_date: Optional[Union[datetime, float]] = None,
+        sort_by: Optional[SortBy] = None,
+        sort_order: Optional[SortOrder] = None,
     ):
         self.types = types
         self.refs = refs
@@ -132,6 +161,8 @@ def __init__(
         self.chains = chains
         self.start_date = start_date
         self.end_date = end_date
+        self.sort_by = sort_by
+        self.sort_order = sort_order
 
     def as_http_params(self) -> Dict[str, str]:
         """Convert the filters into a dict that can be used by an `aiohttp` client
@@ -148,6 +179,8 @@ def as_http_params(self) -> Dict[str, str]:
             "chains": serialize_list(self.chains),
             "startDate": _date_field_to_timestamp(self.start_date),
             "endDate": _date_field_to_timestamp(self.end_date),
+            "sortBy": enum_as_str(self.sort_by),
+            "sortOrder": enum_as_str(self.sort_order),
         }
 
         # Ensure all values are strings.
diff --git a/src/aleph/sdk/utils.py b/src/aleph/sdk/utils.py
index 51bb04e5..ab17f44a 100644
--- a/src/aleph/sdk/utils.py
+++ b/src/aleph/sdk/utils.py
@@ -115,12 +115,14 @@ async def copy_async_readable_to_buffer(
         buffer.write(chunk)
 
 
-def enum_as_str(obj: Union[str, Enum]) -> str:
+def enum_as_str(obj: Optional[Union[str, Enum]]) -> Optional[str]:
     """Returns the value of an Enum, or the string itself when passing a string.
 
     Python 3.11 adds a new formatting of string enums.
     `str(MyEnum.value)` becomes `MyEnum.value` instead of `value`.
     """
+    if not obj:
+        return None
     if not isinstance(obj, str):
         raise TypeError(f"Unsupported enum type: {type(obj)}")