diff --git a/tools/offline_signature.ml b/tools/offline_signature.ml
index 1717c851..4d88aff9 100644
--- a/tools/offline_signature.ml
+++ b/tools/offline_signature.ml
@@ -1,4 +1,4 @@
-let _denom_signature master_priv master_pub
+let _denom_signature ~key ~key_pub
     Api.FutureDenom.
       {
         section_name= _;
@@ -28,22 +28,20 @@ let _denom_signature master_priv master_pub
   let master_sig =
     let open Bin_type in
     let open Bin_signature.DenominationKeyValidityPS in
-    let denom_key_validity =
-      {
-        master= master_pub;
-        start= stamp_start;
-        expire_withdraw= stamp_expire_withdraw;
-        expire_spend= stamp_expire_deposit;
-        expire_legal= stamp_expire_legal;
-        value;
-        fee_withdraw;
-        fee_deposit;
-        fee_refresh;
-        denom_hash= DenominationHash.hash pub_octets;
-      }
-    in
-    let data = Bin.to_string bin denom_key_validity in
-    Crypto.EddsaSignature.sign ~key:master_priv data
+    {
+      master= key_pub;
+      start= stamp_start;
+      expire_withdraw= stamp_expire_withdraw;
+      expire_spend= stamp_expire_deposit;
+      expire_legal= stamp_expire_legal;
+      value;
+      fee_withdraw;
+      fee_deposit;
+      fee_refresh;
+      denom_hash= DenominationHash.hash pub_octets;
+    }
+    |> Bin.to_string bin
+    |> Crypto.EddsaSignature.sign ~key
   in
   Api.DenomSignature.{ h_denom_pub; master_sig }