diff --git a/src/bin_sig.ml b/src/bin_sig.ml
index 70d86584..6caece8b 100644
--- a/src/bin_sig.ml
+++ b/src/bin_sig.ml
@@ -92,6 +92,10 @@ end) : sig
 
   val jsont : t Jsont.t
   val caqti : t Caqti_type.t
+
+  (* TODO rm *)
+  (* escape hatch, only needed for /keys `exchange_sig` (signature over contatentation of all of the master_sigs) *)
+  val to_octets : t -> string
 end = struct
   open Crypto
 
@@ -102,6 +106,7 @@ end = struct
   let verify_f ~f t r = f t ~msg:(Bin.to_string R.bin r)
   let jsont = EddsaSignature.jsont
   let caqti : EddsaSignature.t Caqti_type.t = EddsaSignature.caqti
+  let to_octets t = EddsaSignature.to_octets t
 end
 
 module DenominationKeyAnnouncement = struct
diff --git a/src/config.ml b/src/config.ml
index 7c62ffb2..fd098af0 100644
--- a/src/config.ml
+++ b/src/config.ml
@@ -20,9 +20,13 @@ module Exchange = struct
   let port = get "port" |> int
   let bind_to = get "bind_to"
   let master_public_key = get "master_public_key" |> ed25519
+
+  (* TODO Defaults to 0.0 if not specified. *)
   let stefan_abs = get "stefan_abs" |> amount
   let stefan_log = get "stefan_log" |> amount
-  let stefan_lin = get_opt "stefan_lin" |> Option.map float
+
+  let stefan_lin =
+    get_opt "stefan_lin" |> Option.map float |> Option.value ~default:0.0
 
   let aggregator_idle_sleep_interval =
     get "aggregator_idle_sleep_interval" |> duration
diff --git a/src/http_keys.ml b/src/http_keys.ml
index 481c1f57..c19ac2b4 100644
--- a/src/http_keys.ml
+++ b/src/http_keys.ml
@@ -4,6 +4,43 @@ open Syntax
 open Api
 module String_map = Stdlib.Map.Make (Stdlib.String)
 
+let denomgroup_of_denomdata
+    Denom_data.
+      {
+        pub;
+        value;
+        stamp_start;
+        stamp_expire_withdraw;
+        stamp_expire_deposit;
+        stamp_expire_legal;
+        fee_withdraw;
+        fee_deposit;
+        fee_refresh;
+        fee_refund;
+        age_mask;
+        h_pub;
+        master_sig;
+        revoked_sig;
+      } =
+  let master_sig = match master_sig with None -> assert false | Some v -> v in
+  let denoms =
+    [
+      RsaDenom.
+        {
+          rsa_pub= pub;
+          master_sig;
+          stamp_start;
+          stamp_expire_withdraw;
+          stamp_expire_deposit;
+          stamp_expire_legal;
+          lost= None;
+        };
+    ]
+  in
+  DenomGroup.Rsa
+    RsaDenomGroup.
+      { denoms; value; fee_withdraw; fee_deposit; fee_refresh; fee_refund }
+
 let mk_keys ~db_conn ~sm ~last_issue_date =
   let version = "0" in
   let base_url = Config.base_url in
@@ -51,12 +88,97 @@ let mk_keys ~db_conn ~sm ~last_issue_date =
   let kyc_enabled = false in
   let disable_direct_deposit = (* todo *) false in
   let master_public_key = Config.master_public_key in
-  let reserve_closing_delay = Config.Exchangedb.idle_reserve_expiration_time in
+  let reserve_closing_delay =
+    Some Config.Exchangedb.idle_reserve_expiration_time
+  in
   (* todo *)
   let wallet_balance_limit_without_kyc = None in
   let hard_limits = [] in
   let zero_limits = [] in
-  (*
+  let* denom_data_l = Pg.get_denominations db_conn |> unwrap_err_caqti in
+  (* TODO check order!! *)
+  let denom_data_l =
+    List.sort
+      (fun a b ->
+        let open Denom_data in
+        Stdlib.compare a.stamp_start b.stamp_start)
+      denom_data_l
+  in
+  let list_issue_date =
+    (* TODO is this the last [stamp_start] value? *)
+    (* date when the denomination keys were last updated *)
+    match denom_data_l with
+    | [] -> None
+    | v :: _ -> v.stamp_start
+  in
+  let denominations =
+    (* TODO really need to understand and correctly group denoms
+       'exchange_sig' depends on correct denom group/order *)
+    List.map denomgroup_of_denomdata denom_data_l
+  in
+
+  let* signkeys =
+    let+ signkey_data_l = Pg.get_active_signkeys db_conn |> unwrap_err_caqti in
+    let signkey_data_l =
+      List.sort
+        (fun a b ->
+          let open Signkey_data in
+          Stdlib.compare a.stamp_start b.stamp_start)
+        signkey_data_l
+    in
+    List.map
+      (fun Signkey_data.
+             {
+               pub;
+               stamp_start;
+               stamp_expire;
+               stamp_end;
+               master_sig;
+               revoked_sig= _;
+             } ->
+        let master_sig =
+          match master_sig with
+          | None -> Fmt.failwith "signkey_data without master_sig"
+          | Some v -> v
+        in
+        SignKey.{ key= pub; stamp_start; stamp_expire; stamp_end; master_sig })
+      signkey_data_l
+  in
+
+  let exchange_pub =
+    (* the eddsa pub key used to sign exchange_sig *)
+    match signkeys with
+    | [] -> Fmt.failwith "exchange has no active signkey"
+    | v :: _ -> v.SignKey.key
+  in
+  let exchange_sig =
+    (* Compact EdDSA signature (binary-only) over the
+       contatentation of all of the master_sigs (in reverse
+       chronological order by group) in the arrays under "denominations". *)
+    let l =
+      List.map
+        (fun v ->
+          match v.Denom_data.master_sig with
+          | None -> Fmt.failwith "denom_data without master_sig"
+          | Some v -> v)
+        denom_data_l
+    in
+    let l = List.map (fun v -> Bin_sig.DenominationKeyValidity.to_octets v) l in
+    let data = String.concat "" l in
+    let hc = Bin_type.Hash_64.hash data in
+    let open Bin_sig.ExchangeKeySet in
+    sign_f
+      ~f:(Secmod.sign_with_signkey sm ~pub:exchange_pub)
+      R.{ list_issue_date; hc }
+  in
+
+  let recoup = [] in
+  let global_fees = (* TODO *) [] in
+  let auditors = (* TODO *) [] in
+  let extensions = None in
+  let extensions_sig = None in
+  Ok
+    ExchangeKeysResponse.
       {
         version;
         base_url;
@@ -92,8 +214,6 @@ let mk_keys ~db_conn ~sm ~last_issue_date =
         extensions;
         extensions_sig;
       }
-      *)
-  assert false
 
 let jsont = ExchangeKeysResponse.jsont
 
diff --git a/src/mte.ml b/src/mte.ml
index c6c3424e..d2767816 100644
--- a/src/mte.ml
+++ b/src/mte.ml
@@ -26,7 +26,7 @@ let routes =
   let open Vif.Type in
   let get_ path = get (path /?? nil) in
   let post path jsont = post (json_encoding jsont) (path /?? nil) in
-  let static =
+  let tos =
     let v s = rel / s in
     [
       get_ rel --> hello;
@@ -34,6 +34,7 @@ let routes =
       get_ (v "privacy") --> Static.privacy;
     ]
   in
+  let status_info = [ get_ (rel / "keys") --> Http_keys.f ] in
   let management =
     let open Http_management in
     let v s = rel / "management" / s in
@@ -56,7 +57,7 @@ let routes =
       post (v "partners") Partners.jsont --> Partners.f;
     ]
   in
-  static @ management
+  tos @ status_info @ management
 
 let () =
   Util.Log_reporter.setup ();
diff --git a/src/pg.ml b/src/pg.ml
index 1a2dce80..7ff7a010 100644
--- a/src/pg.ml
+++ b/src/pg.ml
@@ -61,7 +61,7 @@ let get_active_signkeys =
        esk_serial FROM signkey_revocations skr WHERE esk.esk_serial = \
        skr.esk_serial)"
   in
-  fun (module Conn : CONN) () ->
+  fun (module Conn : CONN) ->
     let now = Ptime_clock.now () |> Option.some in
     Conn.collect_list get_active_signkeys now
 
diff --git a/src/secmod.mli b/src/secmod.mli
index 9dda7677..9262bf65 100644
--- a/src/secmod.mli
+++ b/src/secmod.mli
@@ -1,3 +1,4 @@
+(* TODO functorize *)
 open Crypto
 
 type t