Shell: allow to prefix signed data by a watermark

src/lib_client_base/client_keys.ml

@@ -127,7 +127,9 @@ module type SIGNER = sig
   val neuterize : secret_key -> public_key Lwt.t
   val public_key : public_key -> Signature.Public_key.t Lwt.t
   val public_key_hash : public_key -> Signature.Public_key_hash.t Lwt.t
-  val sign : secret_key -> MBytes.t -> Signature.t tzresult Lwt.t
+  val sign :
+    ?watermark: Signature.watermark ->
+    secret_key -> MBytes.t -> Signature.t tzresult Lwt.t
 end
 
 let signers_table : (string, (module SIGNER) * bool) Hashtbl.t = Hashtbl.create 13
@@ -149,14 +151,14 @@ let find_signer_for_key cctxt ~scheme =
 let registered_signers () : (string * (module SIGNER)) list =
   Hashtbl.fold (fun k (v, _) acc -> (k, v) :: acc) signers_table []
 
-let sign cctxt ((Sk_locator { scheme }) as skloc) buf =
+let sign ?watermark cctxt ((Sk_locator { scheme }) as skloc) buf =
   find_signer_for_key cctxt ~scheme >>=? fun signer ->
   let module Signer = (val signer : SIGNER) in
   Signer.sk_of_locator skloc >>=? fun t ->
-  Signer.sign t buf
+  Signer.sign ?watermark t buf
 
-let append cctxt loc buf =
-  sign cctxt loc buf >>|? fun signature ->
+let append ?watermark cctxt loc buf =
+  sign ?watermark cctxt loc buf >>|? fun signature ->
   Signature.concat buf signature
 
 let register_key cctxt ?(force=false)

src/lib_client_base/client_keys.mli

@@ -90,8 +90,10 @@ module type SIGNER = sig
   val public_key_hash : public_key -> Signature.Public_key_hash.t Lwt.t
   (** [public_key_hash pk] is the hash of [pk]. *)
 
-  val sign : secret_key -> MBytes.t -> Signature.t tzresult Lwt.t
-  (** [sign sk data] is signature obtained by signing [data] with
+  val sign :
+    ?watermark: Signature.watermark ->
+    secret_key -> MBytes.t -> Signature.t tzresult Lwt.t
+    (** [sign ?watermark sk data] is signature obtained by signing [data] with
         [sk]. *)
 end
 
@@ -103,10 +105,14 @@ val registered_signers : unit -> (string * (module SIGNER)) list
 
 val find_signer_for_key :
   #Client_context.io_wallet -> scheme:string -> (module SIGNER) tzresult Lwt.t
+
 val sign :
+  ?watermark:Signature.watermark ->
   #Client_context.io_wallet ->
   sk_locator -> MBytes.t -> Signature.t tzresult Lwt.t
+
 val append :
+  ?watermark:Signature.watermark ->
   #Client_context.io_wallet ->
   sk_locator -> MBytes.t -> MBytes.t tzresult Lwt.t
 

src/lib_client_base_unix/client_signer_encrypted.ml

@@ -202,7 +202,7 @@ module Encrypted_signer : SIGNER = struct
   let neuterize x = Lwt.return (Signature.Secret_key.to_public_key x)
   let public_key x = Lwt.return x
   let public_key_hash x = Lwt.return (Signature.Public_key.hash x)
-  let sign t buf = return (Signature.sign t buf)
+  let sign ?watermark t buf = return (Signature.sign ?watermark t buf)
 end
 
 let () =

src/lib_client_base_unix/client_signer_unencrypted.ml

@@ -59,7 +59,7 @@ module Unencrypted_signer : SIGNER = struct
   let neuterize x = Lwt.return (Signature.Secret_key.to_public_key x)
   let public_key x = Lwt.return x
   let public_key_hash x = Lwt.return (Signature.Public_key.hash x)
-  let sign t buf = return (Signature.sign t buf)
+  let sign ?watermark t buf = return (Signature.sign ?watermark t buf)
 end
 
 let () =

src/lib_crypto/ed25519.ml

@@ -225,6 +225,8 @@ end
 
 type t = MBytes.t
 
+type watermark = MBytes.t
+
 let name = "Ed25519"
 let title = "An Ed25519 signature"
 
@@ -284,12 +286,24 @@ let pp ppf t = Format.fprintf ppf "%s" (to_b58check t)
 
 let zero = MBytes.make size '\000'
 
-let sign sk msg =
+let sign ?watermark sk msg =
+  let msg =
+    Blake2B.to_bytes @@
+    Blake2B.hash_bytes @@
+    match watermark with
+    | None -> [msg]
+    | Some prefix -> [ prefix ; msg ] in
   let signature = MBytes.create Sign.bytes in
   Sign.sign ~sk ~msg ~signature ;
   signature
 
-let check pk signature msg =
+let check ?watermark pk signature msg =
+  let msg =
+    Blake2B.to_bytes @@
+    Blake2B.hash_bytes @@
+    match watermark with
+    | None -> [msg]
+    | Some prefix -> [ prefix ; msg ] in
   Sign.verify ~pk ~signature ~msg
 
 let generate_key ?seed () =

src/lib_crypto/ed25519.mli

@@ -9,5 +9,5 @@
 
 (** Tezos - Ed25519 cryptography *)
 
-include S.SIGNATURE
+include S.SIGNATURE with type watermark = MBytes.t
 include S.RAW_DATA with type t := t

src/lib_crypto/s.ml

@@ -205,8 +205,9 @@ module type SIGNATURE = sig
 
   val zero: t
 
-  val sign: Secret_key.t -> MBytes.t -> t
-  val check: Public_key.t -> t -> MBytes.t -> bool
+  type watermark
+  val sign: ?watermark:watermark -> Secret_key.t -> MBytes.t -> t
+  val check: ?watermark:watermark -> Public_key.t -> t -> MBytes.t -> bool
 
   val generate_key: ?seed:MBytes.t -> unit -> (Public_key_hash.t * Public_key.t * Secret_key.t)
 

src/lib_crypto/secp256k1.ml

@@ -173,6 +173,8 @@ end
 
 type t = Sign.plain Sign.t
 
+type watermark = MBytes.t
+
 let name = "Secp256k1"
 let title = "A Secp256k1 signature"
 
@@ -239,10 +241,22 @@ let pp ppf t = Format.fprintf ppf "%s" (to_b58check t)
 
 let zero = of_bytes_exn (MBytes.make size '\000')
 
-let sign sk msg =
+let sign ?watermark sk msg =
+  let msg =
+    Blake2B.to_bytes @@
+    Blake2B.hash_bytes @@
+    match watermark with
+    | None -> [msg]
+    | Some prefix -> [ prefix ; msg ] in
   Sign.sign_exn context ~sk msg
 
-let check public_key signature msg =
+let check ?watermark public_key signature msg =
+  let msg =
+    Blake2B.to_bytes @@
+    Blake2B.hash_bytes @@
+    match watermark with
+    | None -> [msg]
+    | Some prefix -> [ prefix ; msg ] in
   Sign.verify_exn context ~pk:public_key ~msg ~signature
 
 let generate_key ?(seed=Rand.generate 32) () =

src/lib_crypto/secp256k1.mli

@@ -9,6 +9,5 @@
 
 (** Tezos - Secp256k1 cryptography *)
 
-include S.SIGNATURE
-
+include S.SIGNATURE with type watermark = MBytes.t
 include S.RAW_DATA with type t := t

src/lib_crypto/signature.ml

@@ -21,6 +21,12 @@ type secret_key =
   | Ed25519 of Ed25519.Secret_key.t
   | Secp256k1 of Secp256k1.Secret_key.t
 
+type watermark =
+  | Block_header
+  | Endorsement
+  | Generic_operation
+  | Custom of MBytes.t
+
 module Public_key_hash = struct
 
   type t = public_key_hash =
@@ -432,37 +438,40 @@ let of_ed25519 s = Ed25519 s
 
 let zero = of_ed25519 Ed25519.zero
 
-let hash msg =
-  Blake2B.(to_bytes (hash_bytes [msg]))
+let bytes_of_watermark = function
+  | Block_header      -> MBytes.of_string "\x01"
+  | Endorsement       -> MBytes.of_string "\x02"
+  | Generic_operation -> MBytes.of_string "\x03"
+  | Custom bytes      -> bytes
 
-let sign secret_key message =
-  let message = hash message in
+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 sk message)
-  | Secret_key.Secp256k1 sk -> of_secp256k1 (Secp256k1.sign sk message)
+  | Secret_key.Ed25519 sk -> of_ed25519 (Ed25519.sign ?watermark sk message)
+  | Secret_key.Secp256k1 sk -> of_secp256k1 (Secp256k1.sign ?watermark sk message)
 
-let check public_key signature message =
-  let message = hash message in
+let check ?watermark public_key signature message =
+  let watermark = Option.map ~f:bytes_of_watermark watermark in
   match public_key, signature with
   | Public_key.Ed25519 pk, Unknown signature -> begin
       match Ed25519.of_bytes_opt signature with
-      | Some s -> Ed25519.check pk s message
+      | Some s -> Ed25519.check ?watermark pk s message
       | None -> false
     end
   | Public_key.Secp256k1 pk, Unknown signature -> begin
       match Secp256k1.of_bytes_opt signature with
-      | Some s -> Secp256k1.check pk s message
+      | Some s -> Secp256k1.check ?watermark pk s message
       | None -> false
     end
   | Public_key.Ed25519 pk, Ed25519 signature ->
-      Ed25519.check pk signature message
+      Ed25519.check ?watermark pk signature message
   | Public_key.Secp256k1 pk, Secp256k1 signature ->
-      Secp256k1.check pk signature message
+      Secp256k1.check ?watermark pk signature message
   | Public_key.Ed25519 _, Secp256k1 _ -> false
   | Public_key.Secp256k1 _, Ed25519 _ -> false
 
-let append sk msg =
-  MBytes.concat "" [msg; (to_bytes (sign sk msg))]
+let append ?watermark sk msg =
+  MBytes.concat "" [msg; (to_bytes (sign ?watermark sk msg))]
 
 let concat msg signature =
   MBytes.concat "" [msg; (to_bytes signature)]

src/lib_crypto/signature.mli

@@ -19,11 +19,20 @@ type secret_key =
   | Ed25519 of Ed25519.Secret_key.t
   | Secp256k1 of Secp256k1.Secret_key.t
 
+type watermark =
+  | Block_header
+  | Endorsement
+  | Generic_operation
+  | Custom of MBytes.t
+
+val bytes_of_watermark: watermark -> MBytes.t
+
 include S.SIGNATURE with type Public_key_hash.t = public_key_hash
                      and type Public_key.t = public_key
                      and type Secret_key.t = secret_key
+                     and type watermark := watermark
 
-val append : secret_key -> MBytes.t -> MBytes.t
+val append : ?watermark:watermark -> secret_key -> MBytes.t -> MBytes.t
 (** [append sk buf] is the concatenation of [buf] and the
     serialization of the signature of [buf] signed by [sk]. *)
 

src/lib_protocol_environment/sigs/v1/ed25519.mli

@@ -9,4 +9,4 @@
 
 (** Tezos - Ed25519 cryptography *)
 
-include S.SIGNATURE
+include S.SIGNATURE with type watermark := MBytes.t

src/lib_protocol_environment/sigs/v1/s.mli

@@ -244,8 +244,10 @@ module type SIGNATURE = sig
 
   val zero: t
 
+  type watermark
+
   (** Check a signature *)
-  val check: Public_key.t -> t -> MBytes.t -> bool
+  val check: ?watermark:watermark -> Public_key.t -> t -> MBytes.t -> bool
 
 end
 

src/lib_protocol_environment/sigs/v1/secp256k1.mli

@@ -9,4 +9,4 @@
 
 (** Tezos - Secp256k1 cryptography *)
 
-include S.SIGNATURE
+include S.SIGNATURE with type watermark := MBytes.t

src/lib_protocol_environment/sigs/v1/signature.mli

@@ -15,5 +15,12 @@ type public_key =
   | Ed25519 of Ed25519.Public_key.t
   | Secp256k1 of Secp256k1.Public_key.t
 
+type watermark =
+  | Block_header
+  | Endorsement
+  | Generic_operation
+  | Custom of MBytes.t
+
 include S.SIGNATURE with type Public_key_hash.t = public_key_hash
                      and type Public_key.t = public_key
+                     and type watermark := watermark

src/lib_protocol_environment/tezos_protocol_environment.ml

@@ -134,6 +134,7 @@ module Make (Context : CONTEXT) = struct
        and type Signature.public_key_hash = Signature.public_key_hash
        and type Signature.public_key = Signature.public_key
        and type Signature.t = Signature.t
+       and type Signature.watermark = Signature.watermark
        and type 'a Micheline.canonical = 'a Micheline.canonical
        and type ('a, 'b) RPC_path.t = ('a, 'b) RPC_path.t
        and type ('a, 'b) Micheline.node = ('a, 'b) Micheline.node
@@ -313,8 +314,10 @@ module Make (Context : CONTEXT) = struct
 
         val zero: t
 
+        type watermark
+
         (** Check a signature *)
-        val check: Public_key.t -> t -> MBytes.t -> bool
+        val check: ?watermark:watermark -> Public_key.t -> t -> MBytes.t -> bool
 
       end
 

src/lib_protocol_environment/tezos_protocol_environment.mli

@@ -127,6 +127,7 @@ module Make (Context : CONTEXT) : sig
        and type Signature.public_key_hash = Signature.public_key_hash
        and type Signature.public_key = Signature.public_key
        and type Signature.t = Signature.t
+       and type Signature.watermark = Signature.watermark
        and type 'a Micheline.canonical = 'a Micheline.canonical
        and type ('a, 'b) Micheline.node = ('a, 'b) Micheline.node
        and type Data_encoding.json_schema = Data_encoding.json_schema