quickfix rsa_sig shadowing string type

src/crypto.ml

@@ -1,3 +1,4 @@
+(* TODO refacto crypto+hash+fdh_rsa *)
 open Syntax
 
 module Binary_format_rsa = struct
@@ -247,9 +248,18 @@ module RsaPrivateKey = struct
     Jsont.of_of_string ~kind:"RsaPrivateKey" of_b32 ~enc:to_b32
 end
 
-module RsaSignature = struct
+module RsaSignature : sig
+  type t
+
+  val sign : key:RsaPrivateKey.t -> string -> t
+  val jsont : t Jsont.t
+end = struct
   type t = string
 
+  (* decrypt <=> sign *)
+  let sign ~key bmsg =
+    Mirage_crypto_pk.Rsa.decrypt ~crt_hardening:true ~key bmsg
+
   let jsont =
     let of_b32 s = B32.decode s in
     let to_b32 t = B32.encode t in