diff --git a/src/api.ml b/src/api.ml
index ade65cc6..89d9f123 100644
--- a/src/api.ml
+++ b/src/api.ml
@@ -840,3 +840,20 @@ module AggregateTransferFee = struct
     |> mem "sig" MasterWireFeePS.jsont ~enc:sig_
     |> finish
 end
+
+module AuditorDenominationKey = struct
+  type t = {
+    denom_pub_h: HashCode.t;
+    auditor_sig: ExchangeKeyValidityPS.t;
+  }
+
+  let jsont =
+    let make denom_pub_h auditor_sig = { denom_pub_h; auditor_sig } in
+    let denom_pub_h v = v.denom_pub_h in
+    let auditor_sig v = v.auditor_sig in
+    let open Jsont.Object in
+    map ~kind:"AuditorDenominationKey" make
+    |> mem "denom_pub_h" HashCode.jsont ~enc:denom_pub_h
+    |> mem "auditor_sig" ExchangeKeyValidityPS.jsont ~enc:auditor_sig
+    |> finish
+end
diff --git a/src/bin_signature.ml b/src/bin_signature.ml
index ed0cfc71..776a1323 100644
--- a/src/bin_signature.ml
+++ b/src/bin_signature.ml
@@ -635,6 +635,73 @@ module MasterWireFeePS = struct
   include MK (R)
 end
 
+module ExchangeKeyValidityPS = struct
+  module R = struct
+    (* purpose.purpose = TALER_SIGNATURE_AUDITOR_EXCHANGE_KEYS *)
+    type r = {
+      auditor_url_hash: Hash_64_cstr.t;
+      master: MasterPublicKeyP.t;
+      start: TimeAbsoluteNBO.t;
+      expire_withdraw: TimeAbsoluteNBO.t;
+      expire_spend: TimeAbsoluteNBO.t;
+      expire_legal: TimeAbsoluteNBO.t;
+      value: AmountNBO.t;
+      fee_withdraw: AmountNBO.t;
+      fee_deposit: AmountNBO.t;
+      fee_refresh: AmountNBO.t;
+      denom_hash: DenominationHash.t;
+    }
+
+    let bin =
+      let open Bin in
+      Purpose.make_bin Taler_signatures.auditor_exchange_keys @@ fun _purpose ->
+      record
+        (fun
+          _purpose
+          auditor_url_hash
+          master
+          start
+          expire_withdraw
+          expire_spend
+          expire_legal
+          value
+          fee_withdraw
+          fee_deposit
+          fee_refresh
+          denom_hash
+        ->
+          {
+            auditor_url_hash;
+            master;
+            start;
+            expire_withdraw;
+            expire_spend;
+            expire_legal;
+            value;
+            fee_withdraw;
+            fee_deposit;
+            fee_refresh;
+            denom_hash;
+          })
+      |+ Purpose.field _purpose
+      |+ field Hash_64_cstr.bin (fun t -> t.auditor_url_hash)
+      |+ field MasterPublicKeyP.bin (fun t -> t.master)
+      |+ field TimeAbsoluteNBO.bin (fun t -> t.start)
+      |+ field TimeAbsoluteNBO.bin (fun t -> t.expire_withdraw)
+      |+ field TimeAbsoluteNBO.bin (fun t -> t.expire_spend)
+      |+ field TimeAbsoluteNBO.bin (fun t -> t.expire_legal)
+      |+ field AmountNBO.bin (fun t -> t.value)
+      |+ field AmountNBO.bin (fun t -> t.fee_withdraw)
+      |+ field AmountNBO.bin (fun t -> t.fee_deposit)
+      |+ field AmountNBO.bin (fun t -> t.fee_refresh)
+      |+ field DenominationHash.bin (fun t -> t.denom_hash)
+      |> sealr
+  end
+
+  include R
+  include MK (R)
+end
+
 (* ### BIN IMPL END ### *)
 
 module WithdrawRequestPS = struct
@@ -783,23 +850,6 @@ module WireDepositDataPS = struct
   }
 end
 
-module ExchangeKeyValidityPS = struct
-  (* purpose.purpose = TALER_SIGNATURE_AUDITOR_EXCHANGE_KEYS *)
-  type t = {
-    auditor_url_hash: Hash_64_cstr.t;
-    master: MasterPublicKeyP.t;
-    start: TimeAbsoluteNBO.t;
-    expire_withdraw: TimeAbsoluteNBO.t;
-    expire_spend: TimeAbsoluteNBO.t;
-    expire_legal: TimeAbsoluteNBO.t;
-    value: AmountNBO.t;
-    fee_withdraw: AmountNBO.t;
-    fee_deposit: AmountNBO.t;
-    fee_refresh: AmountNBO.t;
-    denom_hash: DenominationHash.t;
-  }
-end
-
 module PaymentResponsePS = struct
   (* purpose.purpose = TALER_SIGNATURE_MERCHANT_PAYMENT_OK *)
   type t = { h_contract_terms: PrivateContractHash.t }