diff --git a/src/api.ml b/src/api.ml
index 8ec12854..9f3b99d0 100644
--- a/src/api.ml
+++ b/src/api.ml
@@ -915,6 +915,10 @@ module SignKey = struct
       Signkey.{ pub; stamp_start; stamp_expire; stamp_end; master_sig } =
     { key= pub; stamp_start; stamp_expire; stamp_end; master_sig }
 
+  let to_signkey { key= pub; stamp_start; stamp_expire; stamp_end; master_sig }
+      =
+    Signkey.{ pub; stamp_start; stamp_expire; stamp_end; master_sig }
+
   let jsont =
     let make key stamp_start stamp_expire stamp_end master_sig =
       { key; stamp_start; stamp_expire; stamp_end; master_sig }
diff --git a/test/validate_response.ml b/test/validate_response.ml
index c0b68b0c..fd6072be 100644
--- a/test/validate_response.ml
+++ b/test/validate_response.ml
@@ -51,7 +51,19 @@ let keys content =
              })
   in
 
-  (* validate exchange_pub *)
+  let* () =
+    let opt =
+      List.find_opt (fun sk -> sk.SignKey.key = v.exchange_pub) v.signkeys
+    in
+    match opt with
+    | None -> Fmt.error "exchange_pub is not in signkeys list"
+    | Some sk ->
+        let sk = SignKey.to_signkey sk in
+        (* todo will need to fake time to validate expired data *)
+        let now = Timestamp.of_ptime (Ptime_clock.now ()) in
+        if Signkey.is_valid_at ~timestamp:now sk then Ok ()
+        else Fmt.error "exchange_pub is not valid at the current time"
+  in
   (* validate exchange_sig *)
 
   (* validate denominations *)