diff --git a/common/protob/messages-crypto.proto b/common/protob/messages-crypto.proto
index f33f9609e..4953e6159 100644
--- a/common/protob/messages-crypto.proto
+++ b/common/protob/messages-crypto.proto
@@ -106,8 +106,8 @@ message CosiCommit {
  * @end
  */
 message CosiCommitment {
-    required bytes commitment = 1;  // Commitment
-    required bytes pubkey = 2;      // Public key
+    optional bytes commitment = 1;  // Commitment
+    optional bytes pubkey = 2;      // Public key
 }
 
 /**
@@ -118,9 +118,9 @@ message CosiCommitment {
  */
 message CosiSign {
     repeated uint32 address_n = 1;          // BIP-32 path to derive the key from master node
-    required bytes data = 2;                // Data to be signed
-    required bytes global_commitment = 3;   // Aggregated commitment
-    required bytes global_pubkey = 4;       // Aggregated public key
+    optional bytes data = 2;                // Data to be signed
+    optional bytes global_commitment = 3;   // Aggregated commitment
+    optional bytes global_pubkey = 4;       // Aggregated public key
 }
 
 /**
diff --git a/core/src/trezor/messages.py b/core/src/trezor/messages.py
index 0d6e7327b..eef91ff02 100644
--- a/core/src/trezor/messages.py
+++ b/core/src/trezor/messages.py
@@ -1993,14 +1993,14 @@ if TYPE_CHECKING:
             return isinstance(msg, cls)
 
     class CosiCommitment(protobuf.MessageType):
-        commitment: "bytes"
-        pubkey: "bytes"
+        commitment: "bytes | None"
+        pubkey: "bytes | None"
 
         def __init__(
             self,
             *,
-            commitment: "bytes",
-            pubkey: "bytes",
+            commitment: "bytes | None" = None,
+            pubkey: "bytes | None" = None,
         ) -> None:
             pass
 
@@ -2010,17 +2010,17 @@ if TYPE_CHECKING:
 
     class CosiSign(protobuf.MessageType):
         address_n: "list[int]"
-        data: "bytes"
-        global_commitment: "bytes"
-        global_pubkey: "bytes"
+        data: "bytes | None"
+        global_commitment: "bytes | None"
+        global_pubkey: "bytes | None"
 
         def __init__(
             self,
             *,
-            data: "bytes",
-            global_commitment: "bytes",
-            global_pubkey: "bytes",
             address_n: "list[int] | None" = None,
+            data: "bytes | None" = None,
+            global_commitment: "bytes | None" = None,
+            global_pubkey: "bytes | None" = None,
         ) -> None:
             pass
 
diff --git a/legacy/firmware/fsm_msg_crypto.h b/legacy/firmware/fsm_msg_crypto.h
index 3aa52dd95..72f2cdb28 100644
--- a/legacy/firmware/fsm_msg_crypto.h
+++ b/legacy/firmware/fsm_msg_crypto.h
@@ -276,6 +276,8 @@ void fsm_msgCosiCommit(const CosiCommit *msg) {
     cosi_nonce_is_set = true;
   }
 
+  resp->has_commitment = true;
+  resp->has_pubkey = true;
   resp->commitment.size = 32;
   resp->pubkey.size = 32;
 
@@ -291,9 +293,11 @@ void fsm_msgCosiSign(const CosiSign *msg) {
 
   CHECK_INITIALIZED
 
-  CHECK_PARAM(msg->global_commitment.size == 32,
+  CHECK_PARAM(msg->has_data, _("No data provided"));
+  CHECK_PARAM(msg->has_global_commitment && msg->global_commitment.size == 32,
               _("Invalid global commitment"));
-  CHECK_PARAM(msg->global_pubkey.size == 32, _("Invalid global pubkey"));
+  CHECK_PARAM(msg->has_global_pubkey && msg->global_pubkey.size == 32,
+              _("Invalid global pubkey"));
 
   if (!cosi_nonce_is_set) {
     fsm_sendFailure(FailureType_Failure_ProcessError, _("CoSi nonce not set"));
diff --git a/python/src/trezorlib/messages.py b/python/src/trezorlib/messages.py
index 480614241..cbb4846fd 100644
--- a/python/src/trezorlib/messages.py
+++ b/python/src/trezorlib/messages.py
@@ -3027,15 +3027,15 @@ class CosiCommit(protobuf.MessageType):
 class CosiCommitment(protobuf.MessageType):
     MESSAGE_WIRE_TYPE = 72
     FIELDS = {
-        1: protobuf.Field("commitment", "bytes", repeated=False, required=True),
-        2: protobuf.Field("pubkey", "bytes", repeated=False, required=True),
+        1: protobuf.Field("commitment", "bytes", repeated=False, required=False, default=None),
+        2: protobuf.Field("pubkey", "bytes", repeated=False, required=False, default=None),
     }
 
     def __init__(
         self,
         *,
-        commitment: "bytes",
-        pubkey: "bytes",
+        commitment: Optional["bytes"] = None,
+        pubkey: Optional["bytes"] = None,
     ) -> None:
         self.commitment = commitment
         self.pubkey = pubkey
@@ -3045,18 +3045,18 @@ class CosiSign(protobuf.MessageType):
     MESSAGE_WIRE_TYPE = 73
     FIELDS = {
         1: protobuf.Field("address_n", "uint32", repeated=True, required=False, default=None),
-        2: protobuf.Field("data", "bytes", repeated=False, required=True),
-        3: protobuf.Field("global_commitment", "bytes", repeated=False, required=True),
-        4: protobuf.Field("global_pubkey", "bytes", repeated=False, required=True),
+        2: protobuf.Field("data", "bytes", repeated=False, required=False, default=None),
+        3: protobuf.Field("global_commitment", "bytes", repeated=False, required=False, default=None),
+        4: protobuf.Field("global_pubkey", "bytes", repeated=False, required=False, default=None),
     }
 
     def __init__(
         self,
         *,
-        data: "bytes",
-        global_commitment: "bytes",
-        global_pubkey: "bytes",
         address_n: Optional[Sequence["int"]] = None,
+        data: Optional["bytes"] = None,
+        global_commitment: Optional["bytes"] = None,
+        global_pubkey: Optional["bytes"] = None,
     ) -> None:
         self.address_n: Sequence["int"] = address_n if address_n is not None else []
         self.data = data