diff --git a/src/http_info.ml b/src/http_info.ml
index 53039402..a8793388 100644
--- a/src/http_info.ml
+++ b/src/http_info.ml
@@ -68,7 +68,7 @@ let mk_keys ~db_conn (module Keys : Keys.S) ~last_issue_date =
       | Some timestamp ->
           List.find_map
             (fun v ->
-              if Timestamp.compare v.Denomination.stamp_start timestamp = 0 then
+              if Timestamp.equal v.Denomination.stamp_start timestamp then
                 Some v.stamp_start
               else None)
             denom_l
@@ -77,20 +77,24 @@ let mk_keys ~db_conn (module Keys : Keys.S) ~last_issue_date =
     | None -> denom_l
     | Some timestamp ->
         List.filter
-          (fun v -> Timestamp.compare v.Denomination.stamp_start timestamp >= 0)
+          (fun v -> Timestamp.geq v.Denomination.stamp_start timestamp)
           denom_l
   in
   let* denominations = Denomination.make_denom_group_sorted denom_l in
 
   let* signkeys = Keys.signkeys () in
-  let signkeys = List.map Api.SignKey.of_signkey signkeys in
 
   (* the eddsa pub key used to sign exchange_sig *)
   let* exchange_pub =
-    match signkeys with
-    | [] -> Fmt.error "exchange has no active signkey"
-    | sk :: _ -> Ok sk.SignKey.key
+    let now = Timestamp.of_ptime (Ptime_clock.now ()) in
+    let opt =
+      List.find_opt (fun sk -> Signkey.is_valid_at ~timestamp:now sk) signkeys
+    in
+    match opt with
+    | None -> Fmt.error "exchange has no active signkey"
+    | Some sk -> Ok sk.pub
   in
+  let signkeys = List.map Api.SignKey.of_signkey signkeys in
 
   (* ! depends on denominations order *)
   let exchange_sig =
diff --git a/src/http_management.ml b/src/http_management.ml
index 47b4a139..1203dce0 100644
--- a/src/http_management.ml
+++ b/src/http_management.ml
@@ -164,7 +164,7 @@ module Auditors = struct
         Logs.info (fun m -> m "enabled auditor");
         ()
     | Some auditor ->
-        if Timestamp.compare auditor.last_change validity_start > 0 then
+        if Timestamp.geq auditor.last_change validity_start then
           Error
             "database has more recent auditor data for this auditor public key"
         else
@@ -200,7 +200,7 @@ module Auditors_disable = struct
     match opt with
     | None -> Error "auditor not found"
     | Some auditor -> (
-        match Timestamp.compare auditor.last_change validity_end > 0 with
+        match Timestamp.geq auditor.last_change validity_end with
         | true ->
             Error
               "database has more recent auditor data for this auditor public \
diff --git a/src/signkey.ml b/src/signkey.ml
index f0035e1f..8d58e117 100644
--- a/src/signkey.ml
+++ b/src/signkey.ml
@@ -7,3 +7,6 @@ type t = {
   stamp_end: Timestamp.t;
   master_sig: Signatures.ExchangeSigningKeyValidity.t;
 }
+
+let is_valid_at ~timestamp sk =
+  Timestamp.geq sk.stamp_start timestamp && Timestamp.lt timestamp sk.stamp_end
diff --git a/src/time.ml b/src/time.ml
index e65cad41..b05cf5fb 100644
--- a/src/time.ml
+++ b/src/time.ml
@@ -97,6 +97,11 @@ module Timestamp = struct
   let never = uint64_max
   let zero = 0L
   let compare = Int64.unsigned_compare
+  let gt a b = compare a b > 0
+  let geq a b = compare a b >= 0
+  let lt a b = compare a b < 0
+  let leq a b = compare a b <= 0
+  let equal a b = compare a b = 0
   let min a b = if compare a b < 0 then a else b
   let max a b = if compare a b > 0 then a else b
 
diff --git a/src/time.mli b/src/time.mli
index ce2e398a..dc4bd841 100644
--- a/src/time.mli
+++ b/src/time.mli
@@ -37,6 +37,11 @@ module Timestamp : sig
   val never : t
   val zero : t
   val compare : t -> t -> int
+  val gt : t -> t -> bool
+  val geq : t -> t -> bool
+  val lt : t -> t -> bool
+  val leq : t -> t -> bool
+  val equal : t -> t -> bool
   val min : t -> t -> t
   val max : t -> t -> t
   val diff : t -> t -> TimeRelative.t