diff --git a/src/lib_crypto/signature.ml b/src/lib_crypto/signature.ml
index 8aec1057e..5b47714e4 100644
--- a/src/lib_crypto/signature.ml
+++ b/src/lib_crypto/signature.ml
@@ -539,7 +539,7 @@ let pp_watermark ppf =
       fprintf ppf "Custom: 0x%s"
         (try String.sub hexed 0 10 ^ "..." with _ ->  hexed)
 
-let sign ?watermark secret_key message =
+let _sign ?watermark secret_key message =
   let watermark = Option.map ~f:bytes_of_watermark watermark in
   match secret_key with
   | Secret_key.Ed25519 sk -> of_ed25519 (Ed25519.sign ?watermark sk message)
@@ -572,6 +572,27 @@ let check ?watermark public_key signature message =
       P256.check ?watermark pk signature message
   | _ -> false
 
+let fake_sign pk_bytes msg =
+  let half = size / 2 in
+  let tmp = MBytes.init size (fun _ -> '0') in
+  let all_or_half buf = Pervasives.min (MBytes.length buf) half in
+  MBytes.blit pk_bytes 0 tmp 0 (all_or_half pk_bytes) ;
+  MBytes.blit msg 0 tmp half (all_or_half msg) ;
+  of_bytes_exn tmp
+
+let fake_check ?watermark pk signature msg =
+  let pk_bytes = Data_encoding.Binary.to_bytes_exn
+      Public_key.encoding pk in
+  if equal signature (fake_sign pk_bytes msg) then true else
+    check ?watermark pk signature msg
+
+let sign ?watermark:_ sk msg =
+  let pk_bytes = Data_encoding.Binary.to_bytes_exn
+      Secret_key.encoding sk in
+  fake_sign pk_bytes msg
+
+let check = fake_check
+
 let append ?watermark sk msg =
   MBytes.concat "" [msg; (to_bytes (sign ?watermark sk msg))]