JJ: Description from the destination commit:

+ denomgroup_of_denomdata

JJ: Description from source commit:
+ wip /keys

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