diff --git a/src/amount.ml b/src/amount.ml
index c5e06082..26b9ed9d 100644
--- a/src/amount.ml
+++ b/src/amount.ml
@@ -84,9 +84,8 @@ let pp =
   in
   fun ppf { sign; currency; value; fraction } ->
     (* TODO
-       depends on the currency's number of fraction digits
-       assumes value and fraction are in bounds *)
-    pf ppf "%a%s:%Ld.%02ld" (Fmt.option pp_sign) sign currency value fraction
+       depends on the currency's number of fraction digits *)
+    pf ppf "%a%s:%Lu.%02lu" (Fmt.option pp_sign) sign currency value fraction
 
 let to_string = Fmt.str "%a" pp
 
diff --git a/src/secmod_rsa.ml b/src/secmod_rsa.ml
index 13d75c9c..dd39264c 100644
--- a/src/secmod_rsa.ml
+++ b/src/secmod_rsa.ml
@@ -55,33 +55,25 @@ type t = {
   ht: (RsaPublicKey.t, key) Hashtbl.t;
 }
 
-(* -- util -- *)
+let parse_filename =
+  let scan_filename s =
+    Scanf.sscanf_opt s "%Lu-%Lu" (fun t1 t2 ->
+        (Absolute.of_s t1, Absolute.of_s t2))
+  in
+  fun fpath -> scan_filename (Fpath.filename fpath)
 
-let time_abs_of_string s =
-  int_of_string_opt s |> Option.map (fun n -> Absolute.of_s (Int64.of_int n))
-
-let t1_t2_of_fpath fpath =
-  let fname = Fpath.filename fpath in
-  match String.split_on_char '-' fname with
-  | [] -> Fmt.failwith "not possible"
-  | [ t1; t2 ] -> (
-      match (time_abs_of_string t1, time_abs_of_string t2) with
-      | None, _ | _, None -> None
-      | Some t1, Some t2 -> Some (t1, t2))
-  | _ -> None
-
-let time_abs_to_string abs =
-  abs
-  |> Timestamp.of_absolute
-  |> Timestamp.to_s
-  |> Option.get
-  |> Int64.to_int
-  |> string_of_int
+let pp_filename =
+  let pp_s ppf abs =
+    abs |> Timestamp.of_absolute |> Timestamp.to_s |> function
+    | None ->
+        (* (= `never`) this should not happen given resonable config value *)
+        Fmt.failwith "encountered timestamp with value `never`"
+    | Some i -> Fmt.pf ppf "%Lu" i
+  in
+  fun ppf (t1, t2) -> Fmt.pf ppf "%a-%a" pp_s t1 pp_s t2
 
 let key_fpath k =
-  let t1 = time_abs_to_string k.t1 in
-  let t2 = time_abs_to_string k.t2 in
-  let fname = Fmt.str "%s-%s" t1 t2 in
+  let fname = Fmt.str "%a" pp_filename (k.t1, k.t2) in
   Fpath.(v Cfg.key_dir / k.section_name / fname)
 
 (* -- IO -- *)
@@ -128,8 +120,8 @@ let gen_key ~section_name t1 t2 =
   let bits = Cfg.rsa_keysize ~section_name in
   let priv, pub = RsaPrivateKey.generate ~bits () in
   Log.debug (fun m ->
-      m "generated key (%s-%s):@,`%s`" (time_abs_to_string t1)
-        (time_abs_to_string t2) (RsaPublicKey.to_b32 pub));
+      m "generated key (%a):@,`%s`" pp_filename (t1, t2)
+        (RsaPublicKey.to_b32 pub));
   { section_name; priv; pub; t1; t2 }
 
 let sort_keys l = List.sort (fun a b -> Absolute.compare a.t2 b.t2) l
@@ -178,7 +170,7 @@ let load_key ~section_name fpath =
   match Fpath.equal (Fpath.normalize fpath) sm_key_fpath with
   | true -> Ok None
   | false -> (
-      match t1_t2_of_fpath fpath with
+      match parse_filename fpath with
       | None -> Fmt.error "invalid file `%a`" Fpath.pp fpath
       | Some (t1, t2) ->
           let* priv = read_rsa fpath in