+ validate exchange_sig

src/denomination.ml

@@ -110,3 +110,11 @@ let make_denom_group_sorted denominations =
     |> List.sort cmp_group
   in
   l
+
+let hash_over_master_sigs denominations =
+  denominations
+  |> List.map (fun (Api.DenomGroup.Rsa g) -> g.Api.RsaDenomGroup.denoms)
+  |> List.concat_map (List.map (fun dn -> dn.Api.RsaDenom.master_sig))
+  |> List.map Signatures.DenominationKeyValidity.to_octets
+  |> String.concat ""
+  |> Hash.H64.hash