diff --git a/src/bin_client/test/demo/main.ml b/src/bin_client/test/demo/main.ml
index 9ee13a452..e28bd2ad8 100644
--- a/src/bin_client/test/demo/main.ml
+++ b/src/bin_client/test/demo/main.ml
@@ -7,15 +7,25 @@
 (*                                                                        *)
 (**************************************************************************)
 
-type operation = Operation_hash.t
-let max_operation_data_length = 42
+type block_header_data = MBytes.t
+type block_header = {
+  shell : Block_header.shell_header ;
+  protocol_data : block_header_data ;
+}
+let block_header_data_encoding =
+  Data_encoding.(obj1 (req "random_data" Variable.bytes))
+
+type operation_data = unit
+type operation = {
+  shell : Operation.shell_header ;
+  protocol_data : operation_data ;
+}
+let operation_data_encoding = Data_encoding.unit
 
 let max_block_length = 42
 let validation_passes = []
 let acceptable_passes _op = []
 
-let parse_operation h _ = Ok h
-
 let compare_operations _ _ = 0
 
 type validation_state = {
@@ -57,16 +67,15 @@ end
 let precheck_block
     ~ancestor_context:_
     ~ancestor_timestamp:_
-    raw_block =
-  Fitness.to_int64 raw_block.Block_header.shell.fitness >>=? fun _ ->
+    (_raw_block : block_header) =
   return ()
 
 let begin_application
     ~predecessor_context:context
     ~predecessor_timestamp:_
     ~predecessor_fitness:_
-    raw_block =
-  Fitness.to_int64 raw_block.Block_header.shell.fitness >>=? fun fitness ->
+    (raw_block : block_header) =
+  Fitness.to_int64 raw_block.shell.fitness >>=? fun fitness ->
   return { context ; fitness }
 
 let begin_construction
diff --git a/src/bin_client/test/test_fork.sh b/src/bin_client/test/test_fork.sh
index 4cb9f0eb9..7c83c80d9 100755
--- a/src/bin_client/test/test_fork.sh
+++ b/src/bin_client/test/test_fork.sh
@@ -20,8 +20,8 @@ sleep 2
 dictator_secret="unencrypted:edsk31vznjHSSpGExDMHYASz45VZqXN4DPxvsa4hAyY8dHM28cZzp6"
 
 # autogenerated from the demo source
-protocol_version="Ps1ZDZdgRP4PFDkzmFpiYtE7gJHioavCMxC96i9zJsK6URwSXSJ"
-protocol_short="Ps1ZDZdgRP4PFD"
+protocol_version="PsbyjqSF59ENfaQxUcRqVa4DXjzUG8gP2NVEGiXpN3GntcXrV8Q"
+protocol_short="PsbyjqSF59ENfa"
 
 bake
 
diff --git a/src/bin_client/test/test_injection.sh b/src/bin_client/test/test_injection.sh
index 7b5c34a40..3a58ac89b 100755
--- a/src/bin_client/test/test_injection.sh
+++ b/src/bin_client/test/test_injection.sh
@@ -14,7 +14,7 @@ show_logs="no"
 sleep 2
 
 # autogenerated from the demo source
-protocol_version="PsxS1brZfzzXCiFwirbMtQr4X5XR6SiHQ46HajpFDdk9GBXR6vy"
+protocol_version="PsbyjqSF59ENfaQxUcRqVa4DXjzUG8gP2NVEGiXpN3GntcXrV8Q"
 
 $admin_client inject protocol "$test_dir/demo"
 $admin_client list protocols
diff --git a/src/bin_client/test/test_injection_alpha.sh b/src/bin_client/test/test_injection_alpha.sh
index 375a49aa9..1ba7f49bd 100755
--- a/src/bin_client/test/test_injection_alpha.sh
+++ b/src/bin_client/test/test_injection_alpha.sh
@@ -20,8 +20,8 @@ sleep 2
 dictator_secret="unencrypted:edsk31vznjHSSpGExDMHYASz45VZqXN4DPxvsa4hAyY8dHM28cZzp6"
 
 # autogenerated from the demo source
-protocol_version="Ps1ZDZdgRP4PFDkzmFpiYtE7gJHioavCMxC96i9zJsK6URwSXSJ"
-protocol_short="Ps1ZDZdgRP4PFD"
+protocol_version="PsbyjqSF59ENfaQxUcRqVa4DXjzUG8gP2NVEGiXpN3GntcXrV8Q"
+protocol_short="PsbyjqSF59ENfa"
 
 bake
 
diff --git a/src/lib_protocol_environment/sigs/v1/updater.mli b/src/lib_protocol_environment/sigs/v1/updater.mli
index 6e36added..1e1d77d8b 100644
--- a/src/lib_protocol_environment/sigs/v1/updater.mli
+++ b/src/lib_protocol_environment/sigs/v1/updater.mli
@@ -67,13 +67,29 @@ module type PROTOCOL = sig
       operation's quota for each pass. *)
   val validation_passes: quota list
 
-  (** The version specific type of operations. *)
-  type operation
+  (** The version specific type of blocks. *)
+  type block_header_data
 
-  (** The parsing / preliminary validation function for
-      operations. Similar to {!parse_block}. *)
-  val parse_operation:
-    Operation_hash.t -> Operation.t -> operation tzresult
+  (** Encoding for version specific part of block headers.  *)
+  val block_header_data_encoding: block_header_data Data_encoding.t
+
+  (** A fully parsed block header. *)
+  type block_header = {
+    shell: Block_header.shell_header ;
+    protocol_data: block_header_data ;
+  }
+
+  (** The version specific type of operations. *)
+  type operation_data
+
+  (** Encoding for version specific part of operations.  *)
+  val operation_data_encoding: operation_data Data_encoding.t
+
+  (** A fully parsed operation. *)
+  type operation = {
+    shell: Operation.shell_header ;
+    protocol_data: operation_data ;
+  }
 
   (** The Validation passes in which an operation can appear.
       For instance [[0]] if it only belongs to the first pass.
@@ -106,7 +122,7 @@ module type PROTOCOL = sig
   val precheck_block:
     ancestor_context: Context.t ->
     ancestor_timestamp: Time.t ->
-    Block_header.t ->
+    block_header ->
     unit tzresult Lwt.t
 
   (** The first step in a block validation sequence. Initializes a
@@ -119,7 +135,7 @@ module type PROTOCOL = sig
     predecessor_context: Context.t ->
     predecessor_timestamp: Time.t ->
     predecessor_fitness: Fitness.t ->
-    Block_header.t ->
+    block_header ->
     validation_state tzresult Lwt.t
 
   (** Initializes a validation context for constructing a new block
@@ -138,7 +154,7 @@ module type PROTOCOL = sig
     predecessor_fitness: Fitness.t ->
     predecessor: Block_hash.t ->
     timestamp: Time.t ->
-    ?protocol_data: MBytes.t ->
+    ?protocol_data: block_header_data ->
     unit -> validation_state tzresult Lwt.t
 
   (** Called after {!begin_application} (or {!begin_construction}) and
diff --git a/src/lib_protocol_environment/tezos_protocol_environment.ml b/src/lib_protocol_environment/tezos_protocol_environment.ml
index 7ce3054fd..a28bd00e0 100644
--- a/src/lib_protocol_environment/tezos_protocol_environment.ml
+++ b/src/lib_protocol_environment/tezos_protocol_environment.ml
@@ -61,9 +61,18 @@ module Make (Context : CONTEXT) = struct
     type 'a tzresult
     val max_block_length: int
     val validation_passes: quota list
-    type operation
-    val parse_operation:
-      Operation_hash.t -> Operation.t -> operation tzresult
+    type block_header_data
+    val block_header_data_encoding: block_header_data Data_encoding.t
+    type block_header = {
+      shell: Block_header.shell_header ;
+      protocol_data: block_header_data ;
+    }
+    type operation_data
+    val operation_data_encoding: operation_data Data_encoding.t
+    type operation = {
+      shell: Operation.shell_header ;
+      protocol_data: operation_data ;
+    }
     val acceptable_passes: operation -> int list
     val compare_operations: operation -> operation -> int
     type validation_state
@@ -71,13 +80,13 @@ module Make (Context : CONTEXT) = struct
     val precheck_block:
       ancestor_context: context ->
       ancestor_timestamp: Time.t ->
-      Block_header.t ->
+      block_header ->
       unit tzresult Lwt.t
     val begin_application:
       predecessor_context: context ->
       predecessor_timestamp: Time.t ->
       predecessor_fitness: Fitness.t ->
-      Block_header.t ->
+      block_header ->
       validation_state tzresult Lwt.t
     val begin_construction:
       predecessor_context: context ->
@@ -86,7 +95,7 @@ module Make (Context : CONTEXT) = struct
       predecessor_fitness: Fitness.t ->
       predecessor: Block_hash.t ->
       timestamp: Time.t ->
-      ?protocol_data: MBytes.t ->
+      ?protocol_data: block_header_data ->
       unit -> validation_state tzresult Lwt.t
     val apply_operation:
       validation_state -> operation -> validation_state tzresult Lwt.t
@@ -150,7 +159,10 @@ module Make (Context : CONTEXT) = struct
     val wrap_error : 'a Error_monad.tzresult -> 'a tzresult
 
     module Lift (P : Updater.PROTOCOL) : PROTOCOL
-      with type operation = P.operation
+      with type block_header_data = P.block_header_data
+       and type block_header = P.block_header
+       and type operation_data = P.operation_data
+       and type operation = P.operation
        and type validation_state = P.validation_state
 
     class ['block] proto_rpc_context :
@@ -642,7 +654,6 @@ module Make (Context : CONTEXT) = struct
       let apply_operation c o =
         apply_operation c o >|= wrap_error
       let finalize_block c = finalize_block c >|= wrap_error
-      let parse_operation h b = parse_operation h b |> wrap_error
       let init c bh = init c bh >|= wrap_error
     end
 
diff --git a/src/lib_protocol_environment/tezos_protocol_environment.mli b/src/lib_protocol_environment/tezos_protocol_environment.mli
index 516d3d604..b58539a73 100644
--- a/src/lib_protocol_environment/tezos_protocol_environment.mli
+++ b/src/lib_protocol_environment/tezos_protocol_environment.mli
@@ -54,9 +54,18 @@ module Make (Context : CONTEXT) : sig
     type 'a tzresult
     val max_block_length: int
     val validation_passes: quota list
-    type operation
-    val parse_operation:
-      Operation_hash.t -> Operation.t -> operation tzresult
+    type block_header_data
+    val block_header_data_encoding: block_header_data Data_encoding.t
+    type block_header = {
+      shell: Block_header.shell_header ;
+      protocol_data: block_header_data ;
+    }
+    type operation_data
+    val operation_data_encoding: operation_data Data_encoding.t
+    type operation = {
+      shell: Operation.shell_header ;
+      protocol_data: operation_data ;
+    }
     val acceptable_passes: operation -> int list
     val compare_operations: operation -> operation -> int
     type validation_state
@@ -64,13 +73,13 @@ module Make (Context : CONTEXT) : sig
     val precheck_block:
       ancestor_context: context ->
       ancestor_timestamp: Time.t ->
-      Block_header.t ->
+      block_header ->
       unit tzresult Lwt.t
     val begin_application:
       predecessor_context: context ->
       predecessor_timestamp: Time.t ->
       predecessor_fitness: Fitness.t ->
-      Block_header.t ->
+      block_header ->
       validation_state tzresult Lwt.t
     val begin_construction:
       predecessor_context: context ->
@@ -79,7 +88,7 @@ module Make (Context : CONTEXT) : sig
       predecessor_fitness: Fitness.t ->
       predecessor: Block_hash.t ->
       timestamp: Time.t ->
-      ?protocol_data: MBytes.t ->
+      ?protocol_data: block_header_data ->
       unit -> validation_state tzresult Lwt.t
     val apply_operation:
       validation_state -> operation -> validation_state tzresult Lwt.t
@@ -143,7 +152,10 @@ module Make (Context : CONTEXT) : sig
     val wrap_error : 'a Error_monad.tzresult -> 'a tzresult
 
     module Lift (P : Updater.PROTOCOL) : PROTOCOL
-      with type operation = P.operation
+      with type block_header_data = P.block_header_data
+       and type block_header = P.block_header
+       and type operation_data = P.operation_data
+       and type operation = P.operation
        and type validation_state = P.validation_state
 
     class ['block] proto_rpc_context :
diff --git a/src/lib_shell/block_validator.ml b/src/lib_shell/block_validator.ml
index b7cc39722..5bdbea669 100644
--- a/src/lib_shell/block_validator.ml
+++ b/src/lib_shell/block_validator.ml
@@ -142,15 +142,31 @@ let apply_block
     operations Proto.validation_passes >>=? fun () ->
   let operation_hashes = List.map (List.map Operation.hash) operations in
   check_liveness chain_state pred hash operation_hashes operations >>=? fun () ->
-  mapi2_s (fun pass -> map2_s begin fun op_hash raw ->
-      Lwt.return (Proto.parse_operation op_hash raw)
-      |> trace (invalid_block hash (Cannot_parse_operation op_hash)) >>=? fun op ->
-      let allowed_pass = Proto.acceptable_passes op in
-      fail_unless (List.mem pass allowed_pass)
-        (invalid_block hash
-           (Unallowed_pass { operation = op_hash ;
-                             pass ; allowed_pass } )) >>=? fun () ->
-      return op
+  begin
+    match
+      Data_encoding.Binary.of_bytes
+        Proto.block_header_data_encoding
+        header.protocol_data with
+    | None ->
+        fail (invalid_block hash Cannot_parse_block_header)
+    | Some protocol_data ->
+        return ({ shell = header.shell ; protocol_data } : Proto.block_header)
+  end >>=? fun header ->
+  mapi2_s (fun pass -> map2_s begin fun op_hash op ->
+      match
+        Data_encoding.Binary.of_bytes
+          Proto.operation_data_encoding
+          op.Operation.proto with
+      | None ->
+          fail (invalid_block hash (Cannot_parse_operation op_hash))
+      | Some protocol_data ->
+          let op = { Proto.shell = op.shell ; protocol_data } in
+          let allowed_pass = Proto.acceptable_passes op in
+          fail_unless (List.mem pass allowed_pass)
+            (invalid_block hash
+               (Unallowed_pass { operation = op_hash ;
+                                 pass ; allowed_pass } )) >>=? fun () ->
+          return op
     end)
     operation_hashes
     operations >>=? fun parsed_operations ->
diff --git a/src/lib_shell/prevalidation.ml b/src/lib_shell/prevalidation.ml
index fbc56aa33..6d4964181 100644
--- a/src/lib_shell/prevalidation.ml
+++ b/src/lib_shell/prevalidation.ml
@@ -82,6 +82,18 @@ let start_prevalidation
   Context.reset_test_chain
     predecessor_context predecessor
     timestamp >>= fun predecessor_context ->
+  begin
+    match protocol_data with
+    | None -> return None
+    | Some protocol_data ->
+        match
+          Data_encoding.Binary.of_bytes
+            Proto.block_header_data_encoding
+            protocol_data
+        with
+        | None -> failwith "Invalid block header"
+        | Some protocol_data -> return (Some protocol_data)
+  end >>=? fun protocol_data ->
   Proto.begin_construction
     ~predecessor_context
     ~predecessor_timestamp
@@ -105,7 +117,13 @@ let prevalidate
   let ops =
     List.map
       (fun (h, op) ->
-         (h, op, Proto.parse_operation h op |> record_trace Parse_error))
+         let parsed_op =
+           match Data_encoding.Binary.of_bytes
+                   Proto.operation_data_encoding
+                   op.Operation.proto with
+           | None -> error Parse_error
+           | Some protocol_data -> Ok ({ shell = op.shell ; protocol_data }: Proto.operation) in
+         (h, op, parsed_op))
       ops in
   let invalid_ops =
     List.filter_map
diff --git a/src/lib_shell/test/test_state.ml b/src/lib_shell/test/test_state.ml
index 429d30589..422d31dae 100644
--- a/src/lib_shell/test/test_state.ml
+++ b/src/lib_shell/test/test_state.ml
@@ -76,6 +76,13 @@ let block _state ?(context = Context_hash.zero) ?(operations = []) (pred: State.
     protocol_data = MBytes.of_string name ;
   }
 
+let parsed_block ({ shell ; protocol_data } : Block_header.t) =
+  let protocol_data =
+    Data_encoding.Binary.of_bytes_exn
+      Proto.block_header_data_encoding
+      protocol_data in
+  ({ shell ; protocol_data } : Proto.block_header)
+
 let build_valid_chain state vtbl pred names =
   Lwt_list.fold_left_s
     (fun pred name ->
@@ -91,7 +98,7 @@ let build_valid_chain state vtbl pred names =
                ~predecessor_context
                ~predecessor_timestamp: pred_header.shell.timestamp
                ~predecessor_fitness: pred_header.shell.fitness
-               block >>=? fun vstate ->
+               (parsed_block block) >>=? fun vstate ->
              (* no operations *)
              Proto.finalize_block vstate
            end >>=? fun ctxt ->
@@ -404,5 +411,5 @@ let wrap (n, f) =
     end
   end
 
-let tests =List.map wrap tests
+let tests = List.map wrap tests
 
diff --git a/src/lib_shell_services/block_validator_errors.ml b/src/lib_shell_services/block_validator_errors.ml
index 158af8321..e2532c4e1 100644
--- a/src/lib_shell_services/block_validator_errors.ml
+++ b/src/lib_shell_services/block_validator_errors.ml
@@ -30,6 +30,7 @@ type block_error =
   | Unallowed_pass of { operation: Operation_hash.t ;
                         pass: int ;
                         allowed_pass: int list }
+  | Cannot_parse_block_header
 
 let block_error_encoding =
   let open Data_encoding in
@@ -213,6 +214,8 @@ let pp_block_error ppf = function
         \ while only the following passes are allowed: @[<h>%a@]"
         Operation_hash.pp_short operation pass
         Format.(pp_print_list pp_print_int) allowed_pass
+  | Cannot_parse_block_header ->
+      Format.fprintf ppf "Failed to parse the block header."
 
 type error +=
   | Invalid_block of
diff --git a/src/lib_shell_services/block_validator_errors.mli b/src/lib_shell_services/block_validator_errors.mli
index fc70e4fe0..619a70823 100644
--- a/src/lib_shell_services/block_validator_errors.mli
+++ b/src/lib_shell_services/block_validator_errors.mli
@@ -30,6 +30,7 @@ type block_error =
   | Unallowed_pass of { operation: Operation_hash.t ;
                         pass: int ;
                         allowed_pass: int list }
+  | Cannot_parse_block_header
 
 type error +=
   | Invalid_block of
diff --git a/src/proto_alpha/lib_baking/client_baking_forge.ml b/src/proto_alpha/lib_baking/client_baking_forge.ml
index 6314cd42f..079e96b77 100644
--- a/src/proto_alpha/lib_baking/client_baking_forge.ml
+++ b/src/proto_alpha/lib_baking/client_baking_forge.ml
@@ -27,10 +27,13 @@ let forge_block_header
     cctxt block >>=? fun stamp_threshold ->
   let rec loop () =
     let proof_of_work_nonce = generate_proof_of_work_nonce () in
-    let protocol_data : Block_header.protocol_data =
-      { priority ; seed_nonce_hash ; proof_of_work_nonce } in
-    if Baking.check_header_proof_of_work_stamp shell protocol_data stamp_threshold then
-      let unsigned_header = Block_header.forge_unsigned shell protocol_data in
+    let contents =
+      { Block_header.priority ; seed_nonce_hash ; proof_of_work_nonce } in
+    if Baking.check_header_proof_of_work_stamp shell contents stamp_threshold then
+      let unsigned_header =
+        Data_encoding.Binary.to_bytes_exn
+          Alpha_context.Block_header.unsigned_encoding
+          (shell, contents) in
       Client_keys.append delegate_sk ~watermark:Block_header unsigned_header
     else
       loop () in
@@ -41,9 +44,11 @@ let empty_proof_of_work_nonce =
     (String.make Constants_repr.proof_of_work_nonce_size  '\000')
 
 let forge_faked_protocol_data ~priority ~seed_nonce_hash =
-  Alpha_context.Block_header.forge_unsigned_protocol_data
-    { priority ; seed_nonce_hash ;
-      proof_of_work_nonce = empty_proof_of_work_nonce }
+  Data_encoding.Binary.to_bytes_exn
+    Alpha_context.Block_header.protocol_data_encoding
+    { contents = { priority ; seed_nonce_hash ;
+                   proof_of_work_nonce = empty_proof_of_work_nonce } ;
+      signature = Signature.zero }
 
 let assert_valid_operations_hash shell_header operations =
   let operations_hash =
@@ -95,13 +100,14 @@ let () =
 let classify_operations (ops: Operation.raw list) =
   let t = Array.make (List.length Proto_alpha.Main.validation_passes) [] in
   List.iter
-    (fun op ->
-       match Operation.parse op with
-       | Ok o ->
+    (fun (op: Operation.raw) ->
+       match Data_encoding.Binary.of_bytes Operation.protocol_data_encoding op.proto with
+       | Some o ->
            List.iter
              (fun pass -> t.(pass) <- op :: t.(pass))
-             (Proto_alpha.Main.acceptable_passes o)
-       | Error _ -> ())
+             (Proto_alpha.Main.acceptable_passes
+                { shell = op.shell ; protocol_data = o })
+       | None -> ())
     ops ;
   Array.fold_right (fun ops acc -> List.rev ops :: acc) t []
 
diff --git a/src/proto_alpha/lib_client/injection.ml b/src/proto_alpha/lib_client/injection.ml
index d4f0200e9..a75d12748 100644
--- a/src/proto_alpha/lib_client/injection.ml
+++ b/src/proto_alpha/lib_client/injection.ml
@@ -31,7 +31,7 @@ let preapply
   get_branch cctxt block branch >>=? fun branch ->
   let bytes =
     Data_encoding.Binary.to_bytes_exn
-      Operation.unsigned_operation_encoding
+      Operation.unsigned_encoding
       ({ branch }, contents) in
   let watermark =
     match contents with
@@ -49,8 +49,7 @@ let preapply
   end >>=? fun signature ->
   let op =
     { shell = { branch } ;
-      contents ;
-      signature } in
+      protocol_data = { contents ; signature } } in
   let oph = Operation.hash op in
   Block_services.hash cctxt block >>=? fun bh ->
   Alpha_services.Helpers.apply_operation cctxt
diff --git a/src/proto_alpha/lib_client/injection.mli b/src/proto_alpha/lib_client/injection.mli
index 053164966..6f08f02a1 100644
--- a/src/proto_alpha/lib_client/injection.mli
+++ b/src/proto_alpha/lib_client/injection.mli
@@ -18,7 +18,7 @@ val preapply:
   Block_services.block ->
   ?branch:int ->
   ?src_sk:Client_keys.sk_uri ->
-  proto_operation ->
+  Operation.contents ->
   result tzresult Lwt.t
 
 val inject_operation:
@@ -27,7 +27,7 @@ val inject_operation:
   ?confirmations:int ->
   ?branch:int ->
   ?src_sk:Client_keys.sk_uri ->
-  proto_operation ->
+  Operation.contents ->
   result tzresult Lwt.t
 
 val originated_contracts: operation_result -> Contract.t list tzresult
diff --git a/src/proto_alpha/lib_client/operation_result.ml b/src/proto_alpha/lib_client/operation_result.ml
index 0aa676c65..f3383b9c4 100644
--- a/src/proto_alpha/lib_client/operation_result.ml
+++ b/src/proto_alpha/lib_client/operation_result.ml
@@ -134,7 +134,8 @@ let pp_balance_updates ppf = function
       Format.fprintf ppf "@[<v 0>%a@]"
         (Format.pp_print_list pp_one) balance_updates
 
-let pp_operation_result ppf ({ contents ; _ }, operation_result) =
+let pp_operation_result ppf
+    ({ protocol_data = { contents ; _ } }, operation_result) =
   Format.fprintf ppf "@[<v 0>" ;
   begin match contents, operation_result with
     | Anonymous_operations ops, Anonymous_operations_result rs ->
diff --git a/src/proto_alpha/lib_protocol/src/alpha_context.ml b/src/proto_alpha/lib_protocol/src/alpha_context.ml
index 00cbeba52..edd744eb0 100644
--- a/src/proto_alpha/lib_protocol/src/alpha_context.ml
+++ b/src/proto_alpha/lib_protocol/src/alpha_context.ml
@@ -27,7 +27,11 @@ end
 
 include Operation_repr
 module Operation = struct
-  type t = operation
+  type t = operation = {
+    shell: Operation.shell_header ;
+    protocol_data: protocol_data ;
+  }
+  let unsigned_encoding = unsigned_operation_encoding
   include Operation_repr
 end
 module Block_header = Block_header_repr
diff --git a/src/proto_alpha/lib_protocol/src/alpha_context.mli b/src/proto_alpha/lib_protocol/src/alpha_context.mli
index 0a71a2b23..a9f39d785 100644
--- a/src/proto_alpha/lib_protocol/src/alpha_context.mli
+++ b/src/proto_alpha/lib_protocol/src/alpha_context.mli
@@ -683,10 +683,14 @@ module Block_header : sig
   type t = {
     shell: Block_header.shell_header ;
     protocol_data: protocol_data ;
-    signature: Signature.t ;
   }
 
   and protocol_data = {
+    contents: contents ;
+    signature: Signature.t ;
+  }
+
+  and contents = {
     priority: int ;
     seed_nonce_hash: Nonce_hash.t option ;
     proof_of_work_nonce: MBytes.t ;
@@ -702,39 +706,27 @@ module Block_header : sig
 
   val encoding: block_header Data_encoding.encoding
   val raw_encoding: raw Data_encoding.t
+  val contents_encoding: contents Data_encoding.t
+  val unsigned_encoding: (shell_header * contents) Data_encoding.t
   val protocol_data_encoding: protocol_data Data_encoding.encoding
   val shell_header_encoding: shell_header Data_encoding.encoding
 
   val max_header_length: int
   (** The maximum size of block headers in bytes *)
 
-  val parse: Block_header.t -> block_header tzresult
-  (** Parse the protocol-specific part of a block header. *)
-
-  val parse_unsigned_protocol_data: MBytes.t -> protocol_data tzresult
-  (** Parse the (unsigned) protocol-specific part of a block header. *)
-
-  val forge_unsigned_protocol_data: protocol_data -> MBytes.t
-  (** [forge_header proto_hdr] is the binary serialization
-      (using [protocol_data_encoding]) of the protocol-specific part
-      of a block header, without the signature. *)
-
-  val forge_unsigned:
-    Block_header.shell_header -> protocol_data -> MBytes.t
-    (** [forge_header shell_hdr proto_hdr] is the binary serialization
-        (using [unsigned_header_encoding]) of a block header,
-        comprising both the shell and the protocol part of the header,
-        without the signature. *)
-
 end
 
 type operation = {
   shell: Operation.shell_header ;
-  contents: proto_operation ;
-  signature: signature option ;
+  protocol_data: protocol_data ;
 }
 
-and proto_operation =
+and protocol_data = {
+  contents: contents ;
+  signature: Signature.t option ;
+}
+
+and contents =
   | Anonymous_operations of anonymous_operation list
   | Sourced_operation of sourced_operation
 
@@ -822,37 +814,35 @@ type internal_operation = {
 
 module Operation : sig
 
+  type nonrec contents = contents
+  val contents_encoding: contents Data_encoding.t
+
+  type nonrec protocol_data = protocol_data
+  val protocol_data_encoding: protocol_data Data_encoding.t
+  val unsigned_encoding: (Operation.shell_header * contents) Data_encoding.t
+
   type raw = Operation.t = {
     shell: Operation.shell_header ;
     proto: MBytes.t ;
   }
   val raw_encoding: raw Data_encoding.t
 
-  type t = operation
+  type t = operation = {
+    shell: Operation.shell_header ;
+    protocol_data: protocol_data ;
+  }
   val encoding: operation Data_encoding.t
 
   val hash: operation -> Operation_hash.t
   val hash_raw: raw -> Operation_hash.t
 
-  type error += Cannot_parse_operation (* `Branch *)
-  val parse: Operation.t -> operation tzresult
   val acceptable_passes: operation -> int list
 
-  val parse_proto:
-    MBytes.t -> (proto_operation * signature option) tzresult Lwt.t
-
   type error += Missing_signature (* `Permanent *)
   type error += Invalid_signature (* `Permanent *)
 
   val check_signature: public_key -> operation -> unit tzresult Lwt.t
 
-  val forge: Operation.shell_header -> proto_operation -> MBytes.t
-
-  val proto_operation_encoding: proto_operation Data_encoding.t
-
-  val unsigned_operation_encoding:
-    (Operation.shell_header * proto_operation) Data_encoding.t
-
   val internal_operation_encoding: internal_operation Data_encoding.t
 
 end
diff --git a/src/proto_alpha/lib_protocol/src/alpha_services.ml b/src/proto_alpha/lib_protocol/src/alpha_services.ml
index 48df38479..f640afbeb 100644
--- a/src/proto_alpha/lib_protocol/src/alpha_services.ml
+++ b/src/proto_alpha/lib_protocol/src/alpha_services.ml
@@ -51,6 +51,25 @@ module S = struct
 
 end
 
+let parse_operation (op: Operation.raw) =
+  match Data_encoding.Binary.of_bytes
+          Operation.protocol_data_encoding
+          op.proto with
+  | Some protocol_data ->
+      ok { shell = op.shell ; protocol_data }
+  | None -> error Helpers_services.Cannot_parse_operation
+
+let parse_block_header
+    ({ shell ; protocol_data } : Block_header.raw) : Block_header.t tzresult =
+  match
+    Data_encoding.Binary.of_bytes
+      Block_header.protocol_data_encoding
+      protocol_data
+  with
+  | None -> Error [Helpers_services.Cant_parse_block_header]
+  | Some protocol_data -> Ok { shell ; protocol_data }
+
+
 let () =
   let open Services_registration in
   register0_fullctxt S.operations begin fun ctxt () () ->
@@ -58,21 +77,21 @@ let () =
     ctxt.operations () >>= fun operations ->
     map2_s
       (map2_s (fun h op ->
-           Lwt.return (Operation.parse op) >>=? fun op ->
+           Lwt.return (parse_operation op) >>=? fun op ->
            return (h, op)))
       operation_hashes operations
   end ;
   register0_fullctxt S.header begin fun { block_header ; _ } () () ->
-    Lwt.return (Block_header.parse block_header) >>=? fun block_header ->
+    Lwt.return (parse_block_header block_header) >>=? fun block_header ->
     return block_header
   end ;
   register0_fullctxt S.priority begin fun { block_header ; _ } () () ->
-    Lwt.return (Block_header.parse block_header) >>=? fun block_header ->
-    return block_header.protocol_data.priority
+    Lwt.return (parse_block_header block_header) >>=? fun block_header ->
+    return block_header.protocol_data.contents.priority
   end ;
   opt_register0_fullctxt S.seed_nonce_hash begin fun { block_header ; _ } () ( )->
-    Lwt.return (Block_header.parse block_header) >>=? fun block_header ->
-    return block_header.protocol_data.seed_nonce_hash
+    Lwt.return (parse_block_header block_header) >>=? fun block_header ->
+    return block_header.protocol_data.contents.seed_nonce_hash
   end
 
 let operations ctxt block =
diff --git a/src/proto_alpha/lib_protocol/src/apply.ml b/src/proto_alpha/lib_protocol/src/apply.ml
index 7f21be566..a7e65c8c4 100644
--- a/src/proto_alpha/lib_protocol/src/apply.ml
+++ b/src/proto_alpha/lib_protocol/src/apply.ml
@@ -625,7 +625,7 @@ let apply_anonymous_operation ctxt kind =
       add_rewards ctxt seed_nonce_revelation_tip >>=? fun ctxt ->
       return (ctxt, Seed_nonce_revelation_result [(* FIXME *)])
   | Double_endorsement_evidence { op1 ; op2 } -> begin
-      match op1.contents, op2.contents with
+      match op1.protocol_data.contents, op2.protocol_data.contents with
       | Sourced_operation (Consensus_operation (Endorsements e1)),
         Sourced_operation (Consensus_operation (Endorsements e2))
         when Raw_level.(e1.level = e2.level) &&
@@ -682,10 +682,10 @@ let apply_anonymous_operation ctxt kind =
              last = oldest_level }) >>=? fun () ->
       let level = Level.from_raw ctxt raw_level in
       Roll.baking_rights_owner
-        ctxt level ~priority:bh1.protocol_data.priority >>=? fun delegate1 ->
+        ctxt level ~priority:bh1.protocol_data.contents.priority >>=? fun delegate1 ->
       Baking.check_signature bh1 delegate1 >>=? fun () ->
       Roll.baking_rights_owner
-        ctxt level ~priority:bh2.protocol_data.priority >>=? fun delegate2 ->
+        ctxt level ~priority:bh2.protocol_data.contents.priority >>=? fun delegate2 ->
       Baking.check_signature bh2 delegate2 >>=? fun () ->
       fail_unless
         (Signature.Public_key.equal delegate1 delegate2)
@@ -717,7 +717,7 @@ let apply_anonymous_operation ctxt kind =
 
 let apply_operation ctxt mode pred_block hash operation =
   let ctxt = Contract.init_origination_nonce ctxt hash  in
-  begin match operation.contents with
+  begin match operation.protocol_data.contents with
     | Anonymous_operations ops ->
         fold_left_s
           (fun (ctxt, acc) op ->
@@ -759,9 +759,6 @@ let may_start_new_cycle ctxt =
       return ctxt
 
 let begin_full_construction ctxt pred_timestamp protocol_data =
-  Lwt.return
-    (Block_header.parse_unsigned_protocol_data
-       protocol_data) >>=? fun protocol_data ->
   Baking.check_baking_rights
     ctxt protocol_data pred_timestamp >>=? fun delegate_pk ->
   let delegate_pkh = Signature.Public_key.hash delegate_pk in
@@ -778,10 +775,10 @@ let begin_application ctxt block_header pred_timestamp =
   Baking.check_proof_of_work_stamp ctxt block_header >>=? fun () ->
   Baking.check_fitness_gap ctxt block_header >>=? fun () ->
   Baking.check_baking_rights
-    ctxt block_header.protocol_data pred_timestamp >>=? fun delegate_pk ->
+    ctxt block_header.protocol_data.contents pred_timestamp >>=? fun delegate_pk ->
   Baking.check_signature block_header delegate_pk >>=? fun () ->
   let has_commitment =
-    match block_header.protocol_data.seed_nonce_hash with
+    match block_header.protocol_data.contents.seed_nonce_hash with
     | None -> false
     | Some _ -> true in
   fail_unless
@@ -790,7 +787,7 @@ let begin_application ctxt block_header pred_timestamp =
        { expected = current_level.expected_commitment }) >>=? fun () ->
   let delegate_pkh = Signature.Public_key.hash delegate_pk in
   Baking.freeze_baking_deposit ctxt
-    block_header.protocol_data delegate_pkh >>=? fun (ctxt, deposit) ->
+    block_header.protocol_data.contents delegate_pkh >>=? fun (ctxt, deposit) ->
   let ctxt = Fitness.increase ctxt in
   return (ctxt, delegate_pk, deposit)
 
@@ -818,7 +815,7 @@ let finalize_application ctxt protocol_data delegate =
   return ctxt
 
 let compare_operations op1 op2 =
-  match op1.contents, op2.contents with
+  match op1.protocol_data.contents, op2.protocol_data.contents with
   | Anonymous_operations _, Anonymous_operations _ -> 0
   | Anonymous_operations _, Sourced_operation _ -> -1
   | Sourced_operation _, Anonymous_operations _ -> 1
diff --git a/src/proto_alpha/lib_protocol/src/baking.ml b/src/proto_alpha/lib_protocol/src/baking.ml
index 89462a8ce..dd8a129b7 100644
--- a/src/proto_alpha/lib_protocol/src/baking.ml
+++ b/src/proto_alpha/lib_protocol/src/baking.ml
@@ -251,25 +251,29 @@ let check_hash hash stamp_threshold =
   let word = MBytes.get_int64 bytes 0 in
   Compare.Uint64.(word <= stamp_threshold)
 
-let check_header_proof_of_work_stamp shell protocol_data stamp_threshold =
+let check_header_proof_of_work_stamp shell contents stamp_threshold =
   let hash =
     Block_header.hash
-      { shell ; protocol_data ; signature = Signature.zero } in
+      { shell ; protocol_data = { contents ; signature = Signature.zero } } in
   check_hash hash stamp_threshold
 
 let check_proof_of_work_stamp ctxt block =
   let proof_of_work_threshold = Constants.proof_of_work_threshold ctxt in
   if check_header_proof_of_work_stamp
       block.Block_header.shell
-      block.protocol_data
+      block.protocol_data.contents
       proof_of_work_threshold then
     return ()
   else
     fail Invalid_stamp
 
 let check_signature block key =
-  let check_signature key { Block_header.protocol_data ; shell ; signature } =
-    let unsigned_header = Block_header.forge_unsigned shell protocol_data in
+  let check_signature key
+      { Block_header.shell ; protocol_data = { contents ; signature } } =
+    let unsigned_header =
+      Data_encoding.Binary.to_bytes_exn
+        Block_header.unsigned_encoding
+        (shell, contents) in
     Signature.check ~watermark:Block_header key signature unsigned_header in
   if check_signature key block then
     return ()
diff --git a/src/proto_alpha/lib_protocol/src/baking.mli b/src/proto_alpha/lib_protocol/src/baking.mli
index 2b41d71a9..84e207c3e 100644
--- a/src/proto_alpha/lib_protocol/src/baking.mli
+++ b/src/proto_alpha/lib_protocol/src/baking.mli
@@ -39,7 +39,7 @@ val minimal_time: context -> int -> Time.t -> Time.t tzresult Lwt.t
     funds to claim baking rights. *)
 val freeze_baking_deposit:
   context ->
-  Block_header.protocol_data ->
+  Block_header.contents ->
   public_key_hash ->
   (context * Tez.t) tzresult Lwt.t
 
@@ -58,7 +58,7 @@ val freeze_endorsement_deposit:
     * the deposit have been payed if the slot is below [Constants.first_free_baking_slot].
 *)
 val check_baking_rights:
-  context -> Block_header.protocol_data -> Time.t ->
+  context -> Block_header.contents -> Time.t ->
   public_key tzresult Lwt.t
 
 (** [check_endorsements_rights c slots]:
@@ -108,7 +108,7 @@ val check_signature: Block_header.t -> public_key -> unit tzresult Lwt.t
     is does not impact the proof-of-work stamp. The stamp is checked on
     the hash of a block header whose signature has been zeroed-out. *)
 val check_header_proof_of_work_stamp:
-  Block_header.shell_header -> Block_header.protocol_data -> int64 -> bool
+  Block_header.shell_header -> Block_header.contents -> int64 -> bool
 
 (** verify if the proof of work stamp is valid *)
 val check_proof_of_work_stamp:
diff --git a/src/proto_alpha/lib_protocol/src/block_header_repr.ml b/src/proto_alpha/lib_protocol/src/block_header_repr.ml
index 797d08f5b..fe627e69b 100644
--- a/src/proto_alpha/lib_protocol/src/block_header_repr.ml
+++ b/src/proto_alpha/lib_protocol/src/block_header_repr.ml
@@ -9,14 +9,17 @@
 
 (** Block header *)
 
-(** Exported type *)
 type t = {
   shell: Block_header.shell_header ;
   protocol_data: protocol_data ;
-  signature: Signature.t ;
 }
 
 and protocol_data = {
+  contents: contents ;
+  signature: Signature.t ;
+}
+
+and contents = {
   priority: int ;
   seed_nonce_hash: Nonce_hash.t option ;
   proof_of_work_nonce: MBytes.t ;
@@ -30,7 +33,7 @@ type shell_header = Block_header.shell_header
 let raw_encoding = Block_header.encoding
 let shell_header_encoding = Block_header.shell_header_encoding
 
-let protocol_data_encoding =
+let contents_encoding =
   let open Data_encoding in
   conv
     (fun { priority ; seed_nonce_hash ; proof_of_work_nonce } ->
@@ -43,28 +46,31 @@ let protocol_data_encoding =
           (Fixed.bytes Constants_repr.proof_of_work_nonce_size))
        (opt "seed_nonce_hash" Nonce_hash.encoding))
 
-let signed_protocol_data_encoding =
+let protocol_data_encoding =
   let open Data_encoding in
-  merge_objs
-    protocol_data_encoding
-    (obj1 (req "signature" Signature.encoding))
+  conv
+    (fun { contents ; signature } -> (contents, signature))
+    (fun (contents, signature) -> { contents ; signature })
+    (merge_objs
+       contents_encoding
+       (obj1 (req "signature" Signature.encoding)))
 
-let unsigned_header_encoding =
+let unsigned_encoding =
   let open Data_encoding in
   merge_objs
     Block_header.shell_header_encoding
-    protocol_data_encoding
+    contents_encoding
 
 let encoding =
   let open Data_encoding in
   conv
-    (fun { shell ; protocol_data ; signature } ->
-       (shell, (protocol_data, signature)))
-    (fun (shell, (protocol_data, signature)) ->
-       { shell ; protocol_data ; signature })
+    (fun { shell ; protocol_data } ->
+       (shell, protocol_data))
+    (fun (shell, protocol_data) ->
+       { shell ; protocol_data })
     (merge_objs
        Block_header.shell_header_encoding
-       signed_protocol_data_encoding)
+       protocol_data_encoding)
 
 (** Constants *)
 
@@ -74,47 +80,16 @@ let max_header_length =
                  MBytes.create Constants_repr.proof_of_work_nonce_size ;
                seed_nonce_hash = Some Nonce_hash.zero } in
   Data_encoding.Binary.length
-    signed_protocol_data_encoding
-    (fake, Signature.zero)
-
+    protocol_data_encoding
+    { contents = fake ; signature = Signature.zero}
 
 (** Header parsing entry point  *)
 
-type error +=
-  | Cant_parse_protocol_data
-
-let parse
-    ({ shell = { level ; proto_level ; predecessor ;
-                 timestamp ; fitness ; validation_passes ; operations_hash ;
-                 context } ;
-       protocol_data } : Block_header.t) : block_header tzresult =
-  match
-    Data_encoding.Binary.of_bytes signed_protocol_data_encoding protocol_data
-  with
-  | None -> Error [Cant_parse_protocol_data]
-  | Some (protocol_data, signature) ->
-      let shell =
-        { Block_header.level ; proto_level ; predecessor ;
-          timestamp ; fitness ; validation_passes ; operations_hash ;
-          context } in
-      Ok { shell ; protocol_data ; signature }
-
-let parse_unsigned_protocol_data bytes =
-  match Data_encoding.Binary.of_bytes protocol_data_encoding bytes with
-  | None -> Error [Cant_parse_protocol_data]
-  | Some proto -> Ok proto
-
-let forge_unsigned shell proto =
-  Data_encoding.Binary.to_bytes_exn unsigned_header_encoding (shell, proto)
-
-let forge_unsigned_protocol_data proto =
-  Data_encoding.Binary.to_bytes_exn protocol_data_encoding proto
-
 let hash_raw = Block_header.hash
-let hash { shell ; protocol_data ; signature } =
+let hash { shell ; protocol_data } =
   Block_header.hash
     { shell ;
       protocol_data =
         Data_encoding.Binary.to_bytes_exn
-          signed_protocol_data_encoding
-          (protocol_data, signature ) }
+          protocol_data_encoding
+          protocol_data }
diff --git a/src/proto_alpha/lib_protocol/src/block_header_repr.mli b/src/proto_alpha/lib_protocol/src/block_header_repr.mli
index 20e71e472..70966d3b5 100644
--- a/src/proto_alpha/lib_protocol/src/block_header_repr.mli
+++ b/src/proto_alpha/lib_protocol/src/block_header_repr.mli
@@ -7,14 +7,17 @@
 (*                                                                        *)
 (**************************************************************************)
 
-(** Exported type *)
 type t = {
   shell: Block_header.shell_header ;
   protocol_data: protocol_data ;
-  signature: Signature.t ;
 }
 
 and protocol_data = {
+  contents: contents ;
+  signature: Signature.t ;
+}
+
+and contents = {
   priority: int ;
   seed_nonce_hash: Nonce_hash.t option ;
   proof_of_work_nonce: MBytes.t ;
@@ -27,29 +30,13 @@ type shell_header = Block_header.shell_header
 
 val encoding: block_header Data_encoding.encoding
 val raw_encoding: raw Data_encoding.t
+val contents_encoding: contents Data_encoding.t
+val unsigned_encoding: (Block_header.shell_header * contents) Data_encoding.t
 val protocol_data_encoding: protocol_data Data_encoding.encoding
 val shell_header_encoding: shell_header Data_encoding.encoding
 
 val max_header_length: int
 (** The maximum size of block headers in bytes *)
 
-val parse: Block_header.t -> block_header tzresult
-(** Parse the (signed) protocol-specific part of a block header. *)
-
-val parse_unsigned_protocol_data: MBytes.t -> protocol_data tzresult
-(** Parse the (unsigned) protocol-specific part of a block header. *)
-
-val forge_unsigned_protocol_data: protocol_data -> MBytes.t
-(** [forge_header proto_hdr] is the binary serialization
-    (using [protocol_data_encoding]) of the protocol-specific part
-    of a block header, without the signature. *)
-
-val forge_unsigned:
-  Block_header.shell_header -> protocol_data -> MBytes.t
-(** [forge_header shell_hdr proto_hdr] is the binary serialization
-    (using [unsigned_header_encoding]) of a block header,
-    comprising both the shell and the protocol part of the header,
-    without the signature. *)
-
 val hash: block_header -> Block_hash.t
 val hash_raw: raw -> Block_hash.t
diff --git a/src/proto_alpha/lib_protocol/src/helpers_services.ml b/src/proto_alpha/lib_protocol/src/helpers_services.ml
index 4f174d68b..8bb44d682 100644
--- a/src/proto_alpha/lib_protocol/src/helpers_services.ml
+++ b/src/proto_alpha/lib_protocol/src/helpers_services.ml
@@ -9,6 +9,31 @@
 
 open Alpha_context
 
+type error +=
+  | Cannot_parse_operation (* `Branch *)
+  | Cant_parse_block_header
+
+let () =
+  register_error_kind
+    `Branch
+    ~id:"operation.cannot_parse"
+    ~title:"Cannot parse operation"
+    ~description:"The operation is ill-formed \
+                  or for another protocol version"
+    ~pp:(fun ppf () ->
+        Format.fprintf ppf "The operation cannot be parsed")
+    Data_encoding.unit
+    (function Cannot_parse_operation -> Some () | _ -> None)
+    (fun () -> Cannot_parse_operation)
+
+let parse_operation (op: Operation.raw) =
+  match Data_encoding.Binary.of_bytes
+          Operation.protocol_data_encoding
+          op.proto with
+  | Some protocol_data ->
+      ok { shell = op.shell ; protocol_data }
+  | None -> error Cannot_parse_operation
+
 module S = struct
 
   open Data_encoding
@@ -135,13 +160,14 @@ module I = struct
   let apply_operation ctxt () (pred_block, hash, forged_operation, signature) =
     (* ctxt accept_failing_script baker_contract pred_block block_prio operation *)
     match Data_encoding.Binary.of_bytes
-            Operation.unsigned_operation_encoding
+            Operation.unsigned_encoding
             forged_operation with
-    | None -> Error_monad.fail Operation.Cannot_parse_operation
+    | None -> fail Cannot_parse_operation
     | Some (shell, contents) ->
-        let operation = { shell ; contents ; signature } in
-        Apply.apply_operation ctxt Readable pred_block hash operation
-        >>=? fun (_, result) -> return result
+        let operation = { shell ; protocol_data = { contents ; signature } } in
+        Apply.apply_operation
+          ctxt Readable pred_block hash operation >>=? fun (_, result) ->
+        return result
 
 end
 
@@ -259,7 +285,7 @@ module Forge = struct
       RPC_service.post_service
         ~description:"Forge an operation"
         ~query: RPC_query.empty
-        ~input: Operation.unsigned_operation_encoding
+        ~input: Operation.unsigned_encoding
         ~output:
           (obj1
              (req "operation" bytes))
@@ -289,11 +315,13 @@ module Forge = struct
   let () =
     let open Services_registration in
     register0_noctxt S.operations begin fun () (shell, proto) ->
-      return (Operation.forge shell proto)
+      return (Data_encoding.Binary.to_bytes_exn
+                Operation.unsigned_encoding (shell, proto))
     end ;
     register0_noctxt S.protocol_data begin fun ()
       (priority, seed_nonce_hash, proof_of_work_nonce) ->
-      return (Block_header.forge_unsigned_protocol_data
+      return (Data_encoding.Binary.to_bytes_exn
+                Block_header.contents_encoding
                 { priority ; seed_nonce_hash ; proof_of_work_nonce })
     end
 
@@ -489,37 +517,47 @@ module Parse = struct
                 Roll.delegate_pubkey ctxt manager
           end >>=? fun public_key ->
           Operation.check_signature public_key
-            { signature ; shell ; contents }
+            { shell ; protocol_data = { contents ; signature } }
       | Sourced_operation (Consensus_operation (Endorsements { level ; slots ; _ })) ->
           let level = Level.from_raw ctxt level in
           Baking.check_endorsements_rights ctxt level slots >>=? fun public_key ->
           Operation.check_signature public_key
-            { signature ; shell ; contents }
+            { shell ; protocol_data = { contents ; signature } }
       | Sourced_operation (Amendment_operation { source ; _ }) ->
           Roll.delegate_pubkey ctxt source >>=? fun source ->
           Operation.check_signature source
-            { signature ; shell ; contents }
+            { shell ; protocol_data = { contents ; signature } }
       | Sourced_operation (Dictator_operation _) ->
           let key = Constants.dictator_pubkey ctxt in
           Operation.check_signature key
-            { signature ; shell ; contents }
+            { shell ; protocol_data = { contents ; signature } }
 
   end
 
+  let parse_protocol_data protocol_data =
+    match
+      Data_encoding.Binary.of_bytes
+        Block_header.protocol_data_encoding
+        protocol_data
+    with
+    | None -> failwith "Cant_parse_protocol_data"
+    | Some protocol_data -> return protocol_data
+
   let () =
     let open Services_registration in
     register0 S.operations begin fun ctxt () (operations, check) ->
       map_s begin fun raw ->
-        Lwt.return (Operation.parse raw) >>=? fun op ->
+        Lwt.return (parse_operation raw) >>=? fun op ->
         begin match check with
-          | Some true -> I.check_signature ctxt op.signature op.shell op.contents
+          | Some true ->
+              I.check_signature ctxt
+                op.protocol_data.signature op.shell op.protocol_data.contents
           | Some false | None -> return ()
         end >>|? fun () -> op
       end operations
     end ;
     register0_noctxt S.block begin fun () raw_block ->
-      Lwt.return (Block_header.parse raw_block) >>=? fun { protocol_data ; _ } ->
-      return protocol_data
+      parse_protocol_data raw_block.protocol_data
     end
 
   let operations ctxt block ?check operations =
diff --git a/src/proto_alpha/lib_protocol/src/helpers_services.mli b/src/proto_alpha/lib_protocol/src/helpers_services.mli
index afebbfa55..c2189d7bc 100644
--- a/src/proto_alpha/lib_protocol/src/helpers_services.mli
+++ b/src/proto_alpha/lib_protocol/src/helpers_services.mli
@@ -9,6 +9,10 @@
 
 open Alpha_context
 
+type error +=
+  | Cannot_parse_operation (* `Branch *)
+  | Cant_parse_block_header
+
 val minimal_time:
   'a #RPC_context.simple ->
   ?priority:int -> 'a -> Time.t shell_tzresult Lwt.t
diff --git a/src/proto_alpha/lib_protocol/src/main.ml b/src/proto_alpha/lib_protocol/src/main.ml
index 3a40c634c..151d2f10b 100644
--- a/src/proto_alpha/lib_protocol/src/main.ml
+++ b/src/proto_alpha/lib_protocol/src/main.ml
@@ -9,9 +9,22 @@
 
 (* Tezos Protocol Implementation - Protocol Signature Instance *)
 
-type operation = Alpha_context.operation
+type block_header_data = Alpha_context.Block_header.protocol_data
+type block_header = Alpha_context.Block_header.t = {
+  shell: Block_header.shell_header ;
+  protocol_data: block_header_data ;
+}
+
+let block_header_data_encoding = Alpha_context.Block_header.protocol_data_encoding
+
+type operation_data = Alpha_context.Operation.protocol_data
+type operation = Alpha_context.Operation.t = {
+  shell: Operation.shell_header ;
+  protocol_data: operation_data ;
+}
+
+let operation_data_encoding = Alpha_context.Operation.protocol_data_encoding
 
-let parse_operation _hash op = Alpha_context.Operation.parse op
 let acceptable_passes = Alpha_context.Operation.acceptable_passes
 
 let max_block_length =
@@ -36,7 +49,7 @@ type validation_mode =
     }
   | Full_construction of {
       predecessor : Block_hash.t ;
-      protocol_data : Alpha_context.Block_header.protocol_data ;
+      protocol_data : Alpha_context.Block_header.contents ;
       baker : Alpha_context.public_key_hash ;
     }
 
@@ -53,17 +66,15 @@ let current_context { ctxt ; _ } =
 let precheck_block
     ~ancestor_context:_
     ~ancestor_timestamp:_
-    raw_block =
-  Lwt.return (Alpha_context.Block_header.parse raw_block) >>=? fun _ ->
-  (* TODO: decide what other properties should be checked *)
+    _block_header =
+  (* TODO: decide what properties should be checked *)
   return ()
 
 let begin_application
     ~predecessor_context:ctxt
     ~predecessor_timestamp:pred_timestamp
     ~predecessor_fitness:pred_fitness
-    raw_block =
-  Lwt.return (Alpha_context.Block_header.parse raw_block) >>=? fun block_header ->
+    (block_header : Alpha_context.Block_header.t) =
   let level = block_header.shell.level in
   let fitness = pred_fitness in
   let timestamp = block_header.shell.timestamp in
@@ -80,7 +91,7 @@ let begin_construction
     ~predecessor_fitness:pred_fitness
     ~predecessor
     ~timestamp
-    ?protocol_data
+    ?(protocol_data : block_header_data option)
     () =
   let level = Int32.succ pred_level in
   let fitness = pred_fitness in
@@ -94,7 +105,7 @@ let begin_construction
     | Some proto_header ->
         Apply.begin_full_construction
           ctxt pred_timestamp
-          proto_header >>=? fun (ctxt, protocol_data, baker, deposit) ->
+          proto_header.contents >>=? fun (ctxt, protocol_data, baker, deposit) ->
         let mode =
           let baker = Signature.Public_key.hash baker in
           Full_construction { predecessor ; baker ; protocol_data } in
@@ -121,7 +132,7 @@ let finalize_block { mode ; ctxt ; op_count ; deposit = _ } =
       let ctxt = Alpha_context.finalize ctxt in
       return ctxt
   | Application
-      { baker ;  block_header = { protocol_data ; _ } }
+      { baker ;  block_header = { protocol_data = { contents = protocol_data ; _ } ; _ } }
   | Full_construction { protocol_data ; baker ; _ } ->
       Apply.finalize_application ctxt protocol_data baker >>=? fun ctxt ->
       let { level ; _ } : Alpha_context.Level.t =
diff --git a/src/proto_alpha/lib_protocol/src/main.mli b/src/proto_alpha/lib_protocol/src/main.mli
index 15b8f1c51..14adeaa86 100644
--- a/src/proto_alpha/lib_protocol/src/main.mli
+++ b/src/proto_alpha/lib_protocol/src/main.mli
@@ -19,7 +19,7 @@ type validation_mode =
     }
   | Full_construction of {
       predecessor : Block_hash.t ;
-      protocol_data : Alpha_context.Block_header.protocol_data ;
+      protocol_data : Alpha_context.Block_header.contents ;
       baker : Alpha_context.public_key_hash ;
     }
 
@@ -30,5 +30,8 @@ type validation_state =
     deposit : Alpha_context.Tez.t ;
   }
 
-include Updater.PROTOCOL with type operation = Alpha_context.Operation.t
+include Updater.PROTOCOL with type block_header_data = Alpha_context.Block_header.protocol_data
+                          and type block_header = Alpha_context.Block_header.t
+                          and type operation_data = Alpha_context.Operation.protocol_data
+                          and type operation = Alpha_context.operation
                           and type validation_state := validation_state
diff --git a/src/proto_alpha/lib_protocol/src/operation_repr.ml b/src/proto_alpha/lib_protocol/src/operation_repr.ml
index b1fd86a45..6e7f7df57 100644
--- a/src/proto_alpha/lib_protocol/src/operation_repr.ml
+++ b/src/proto_alpha/lib_protocol/src/operation_repr.ml
@@ -18,11 +18,15 @@ let raw_encoding = Operation.encoding
 
 type operation = {
   shell: Operation.shell_header ;
-  contents: proto_operation ;
+  protocol_data: protocol_data ;
+}
+
+and protocol_data = {
+  contents: contents ;
   signature: Signature.t option ;
 }
 
-and proto_operation =
+and contents =
   | Anonymous_operations of anonymous_operation list
   | Sourced_operation of sourced_operation
 
@@ -307,7 +311,7 @@ module Encoding = struct
       (function Dictator_operation op -> Some op | _ -> None)
       (fun op -> Dictator_operation op)
 
-  let signed_operations_case tag =
+  let sourced_operation_case tag =
     case tag
       (union [
           consensus_kind_case (Tag 0) ;
@@ -374,7 +378,7 @@ module Encoding = struct
       )
       (fun ((), id, secret) -> Activation { id ; secret })
 
-  let unsigned_operation_case tag op_encoding =
+  let anonymous_operations_case tag op_encoding =
     case tag
       (obj1
          (req "operations"
@@ -388,40 +392,42 @@ module Encoding = struct
       (function Anonymous_operations ops -> Some ops | _ -> None)
       (fun ops -> Anonymous_operations ops)
 
-  let mu_proto_operation_encoding op_encoding =
+  let contents_encoding op_encoding =
     union [
-      signed_operations_case (Tag 0) ;
-      unsigned_operation_case (Tag 1) op_encoding ;
+      sourced_operation_case (Tag 0) ;
+      anonymous_operations_case (Tag 1) op_encoding ;
     ]
 
-  let mu_signed_proto_operation_encoding op_encoding =
-    merge_objs
-      (mu_proto_operation_encoding op_encoding)
-      (obj1 (varopt "signature" Signature.encoding))
+  let protocol_data_encoding op_encoding =
+    conv
+      (fun { contents ; signature } -> (contents, signature))
+      (fun (contents, signature) -> { contents ; signature })
+      (merge_objs
+         (contents_encoding op_encoding)
+         (obj1 (varopt "signature" Signature.encoding)))
 
   let operation_encoding =
     mu "operation"
       (fun encoding ->
          conv
-           (fun { shell ; contents ; signature } ->
-              (shell, (contents, signature)))
-           (fun (shell, (contents, signature)) ->
-              { shell ; contents ; signature })
+           (fun { shell ; protocol_data } -> (shell, protocol_data))
+           (fun (shell, protocol_data) -> { shell ; protocol_data })
            (merge_objs
               Operation.shell_header_encoding
-              (mu_signed_proto_operation_encoding encoding)))
+              (protocol_data_encoding encoding)))
 
-  let proto_operation_encoding =
-    mu_proto_operation_encoding operation_encoding
 
-  let signed_proto_operation_encoding =
-    mu_signed_proto_operation_encoding operation_encoding
+  let contents_encoding =
+    contents_encoding operation_encoding
+
+  let protocol_data_encoding =
+    protocol_data_encoding operation_encoding
 
   let unsigned_operation_encoding =
     def "operation.alpha.unsigned_operation" @@
     merge_objs
       Operation.shell_header_encoding
-      proto_operation_encoding
+      contents_encoding
 
   let internal_operation_encoding =
     conv
@@ -439,33 +445,14 @@ module Encoding = struct
            ]))
 end
 
-type error += Cannot_parse_operation
-
 let encoding = Encoding.operation_encoding
-
-let () =
-  register_error_kind
-    `Branch
-    ~id:"operation.cannot_parse"
-    ~title:"Cannot parse operation"
-    ~description:"The operation is ill-formed \
-                  or for another protocol version"
-    ~pp:(fun ppf () ->
-        Format.fprintf ppf "The operation cannot be parsed")
-    Data_encoding.unit
-    (function Cannot_parse_operation -> Some () | _ -> None)
-    (fun () -> Cannot_parse_operation)
-
-let parse (op: Operation.t) =
-  match Data_encoding.Binary.of_bytes
-          Encoding.signed_proto_operation_encoding
-          op.proto with
-  | Some (contents, signature) ->
-      ok { shell = op.shell ; contents ; signature }
-  | None -> error Cannot_parse_operation
+let contents_encoding = Encoding.contents_encoding
+let protocol_data_encoding = Encoding.protocol_data_encoding
+let unsigned_operation_encoding = Encoding.unsigned_operation_encoding
+let internal_operation_encoding = Encoding.internal_operation_encoding
 
 let acceptable_passes op =
-  match op.contents with
+  match op.protocol_data.contents with
   | Sourced_operation (Consensus_operation _) -> [0]
   | Sourced_operation (Amendment_operation _ | Dictator_operation _) -> [1]
   | Anonymous_operations _ -> [2]
@@ -498,18 +485,16 @@ let () =
     (function Missing_signature -> Some () | _ -> None)
     (fun () -> Missing_signature)
 
-let forge shell proto =
-  Data_encoding.Binary.to_bytes_exn
-    Encoding.unsigned_operation_encoding (shell, proto)
-
-let check_signature key { shell ; contents ; signature } =
-  match contents, signature with
+let check_signature key { shell ; protocol_data } =
+  match protocol_data.contents, protocol_data.signature with
   | Anonymous_operations _, _ -> return ()
   | Sourced_operation _, None ->
       fail Missing_signature
   | Sourced_operation (Consensus_operation _), Some signature ->
       (* Safe for baking *)
-      let unsigned_operation = forge shell contents in
+      let unsigned_operation =
+        Data_encoding.Binary.to_bytes_exn
+          unsigned_operation_encoding (shell, protocol_data.contents) in
       if Signature.check
           ~watermark:Endorsement
           key signature unsigned_operation then
@@ -518,7 +503,9 @@ let check_signature key { shell ; contents ; signature } =
         fail Invalid_signature
   | Sourced_operation _, Some signature ->
       (* Unsafe for baking *)
-      let unsigned_operation = forge shell contents in
+      let unsigned_operation =
+        Data_encoding.Binary.to_bytes_exn
+          unsigned_operation_encoding (shell, protocol_data.contents) in
       if Signature.check
           ~watermark:Generic_operation
           key signature unsigned_operation then
@@ -526,19 +513,10 @@ let check_signature key { shell ; contents ; signature } =
       else
         fail Invalid_signature
 
-let parse_proto bytes =
-  match Data_encoding.Binary.of_bytes
-          Encoding.signed_proto_operation_encoding
-          bytes with
-  | Some (proto, signature) -> return (proto, signature)
-  | None -> fail Cannot_parse_operation
-
 let hash_raw = Operation.hash
 let hash o =
   let proto =
     Data_encoding.Binary.to_bytes_exn
-      Encoding.signed_proto_operation_encoding
-      (o.contents, o.signature) in
+      protocol_data_encoding
+      o.protocol_data in
   Operation.hash { shell = o.shell ; proto }
-
-include Encoding
diff --git a/src/proto_alpha/lib_protocol/src/operation_repr.mli b/src/proto_alpha/lib_protocol/src/operation_repr.mli
index 374ab7239..bdd855b5d 100644
--- a/src/proto_alpha/lib_protocol/src/operation_repr.mli
+++ b/src/proto_alpha/lib_protocol/src/operation_repr.mli
@@ -18,11 +18,15 @@ val raw_encoding: raw Data_encoding.t
 
 type operation = {
   shell: Operation.shell_header ;
-  contents: proto_operation ;
+  protocol_data: protocol_data ;
+}
+
+and protocol_data = {
+  contents: contents ;
   signature: Signature.t option ;
 }
 
-and proto_operation =
+and contents =
   | Anonymous_operations of anonymous_operation list
   | Sourced_operation of sourced_operation
 
@@ -102,21 +106,16 @@ and dictator_operation =
 
 and counter = Int32.t
 
-type error += Cannot_parse_operation (* `Branch *)
-
 val encoding: operation Data_encoding.t
+val contents_encoding: contents Data_encoding.t
+val protocol_data_encoding: protocol_data Data_encoding.t
+val unsigned_operation_encoding: (Operation.shell_header * contents) Data_encoding.t
 
 val hash_raw: raw -> Operation_hash.t
 val hash: operation -> Operation_hash.t
 
-val parse: Operation.t -> operation tzresult
-
 val acceptable_passes: operation -> int list
 
-val parse_proto:
-  MBytes.t ->
-  (proto_operation * Signature.t option) tzresult Lwt.t
-
 type error += Missing_signature (* `Permanent *)
 type error += Invalid_signature (* `Permanent *)
 
@@ -124,14 +123,6 @@ type error += Invalid_signature (* `Permanent *)
 val check_signature:
   Signature.Public_key.t -> operation -> unit tzresult Lwt.t
 
-val forge: Operation.shell_header -> proto_operation -> MBytes.t
-
-val proto_operation_encoding:
-  proto_operation Data_encoding.t
-
-val unsigned_operation_encoding:
-  (Operation.shell_header * proto_operation) Data_encoding.t
-
 type internal_operation = {
   source: Contract_repr.contract ;
   operation: manager_operation ;
diff --git a/src/proto_alpha/lib_protocol/test/helpers/helpers_apply.mli b/src/proto_alpha/lib_protocol/test/helpers/helpers_apply.mli
index f0c8a909f..0bf74fb9a 100644
--- a/src/proto_alpha/lib_protocol/test/helpers/helpers_apply.mli
+++ b/src/proto_alpha/lib_protocol/test/helpers/helpers_apply.mli
@@ -14,7 +14,7 @@ open Alpha_context
 
 val operation :
   tc:context -> ?src:Helpers_account.t ->
-  Block_hash.t -> Tezos_base.Operation.shell_header -> proto_operation ->
+  Block_hash.t -> Tezos_base.Operation.shell_header -> Operation.contents ->
   (Contract.contract list * context) proto_tzresult Lwt.t
 
 val transaction :
diff --git a/src/proto_alpha/lib_protocol/test/helpers/helpers_block.ml b/src/proto_alpha/lib_protocol/test/helpers/helpers_block.ml
index 555123fdb..d30eff927 100644
--- a/src/proto_alpha/lib_protocol/test/helpers/helpers_block.ml
+++ b/src/proto_alpha/lib_protocol/test/helpers/helpers_block.ml
@@ -13,12 +13,13 @@ open Error_monad
 type shell_header = Block_header.shell_header
 type tezos_header = Block_header.t
 type protocol_data = Proto_alpha.Alpha_context.Block_header.protocol_data
+type contents = Proto_alpha.Alpha_context.Block_header.contents
 type operation_header = Operation.shell_header
 
 type init_block = {
   pred_block_hash : Block_hash.t ;
   pred_shell_header : shell_header ;
-  protocol_data : protocol_data ;
+  protocol_data : contents ;
   op_header : operation_header ;
   sourced_operations : (Proto_alpha.Main.operation * Helpers_account.t) list ;
   operation_hashs : Operation_hash.t list ;
@@ -40,7 +41,7 @@ let get_op_header_res (res : result) : operation_header = {
   branch = res.hash
 }
 
-let get_protocol_data priority commit : protocol_data = {
+let get_protocol_data priority commit : Alpha_context.Block_header.contents = {
   priority ;
   proof_of_work_nonce = Helpers_crypto.generate_proof_of_work_nonce ();
   seed_nonce_hash =
@@ -68,7 +69,8 @@ let init (pred_shell_header : shell_header) pred_block_hash
   let (sourced_operations, operation_hashs) = List.split src_ops_hashs in
   let protocol_data = get_protocol_data priority true in
   let protocol_data_bytes =
-    Proto_alpha.Alpha_context.Block_header.forge_unsigned_protocol_data
+    Data_encoding.Binary.to_bytes_exn
+      Proto_alpha.Alpha_context.Block_header.contents_encoding
       protocol_data
   in
   let timestamp =
@@ -155,7 +157,9 @@ let begin_construction_pre (init_block: init_block) =
     ~predecessor_fitness: init_block.pred_shell_header.fitness
     ~predecessor: init_block.pred_block_hash
     ~timestamp: init_block.timestamp
-    ~protocol_data: init_block.protocol_data_bytes
+    ~protocol_data:
+      (Alpha_context.Block_header.{ contents = init_block.protocol_data ;
+                                    signature = Signature.zero })
     ()
 
 
diff --git a/src/proto_alpha/lib_protocol/test/helpers/helpers_block.mli b/src/proto_alpha/lib_protocol/test/helpers/helpers_block.mli
index b3d8a4948..8812c4f0d 100644
--- a/src/proto_alpha/lib_protocol/test/helpers/helpers_block.mli
+++ b/src/proto_alpha/lib_protocol/test/helpers/helpers_block.mli
@@ -14,13 +14,14 @@ open Proto_alpha
 type shell_header = Block_header.shell_header
 type tezos_header = Block_header.t
 type protocol_data = Alpha_context.Block_header.protocol_data
+type contents = Proto_alpha.Alpha_context.Block_header.contents
 type operation_header = Operation.shell_header
 
 (** Block before application *)
 type init_block = {
   pred_block_hash : Block_hash.t;
   pred_shell_header : shell_header;
-  protocol_data : protocol_data;
+  protocol_data : contents;
   op_header : operation_header;
   sourced_operations :
     (Main.operation * Helpers_account.t) list;
@@ -40,20 +41,20 @@ type result = {
   tezos_context : Alpha_context.t;
 }
 val get_op_header_res : result -> operation_header
-val get_protocol_data : int -> bool -> protocol_data
+val get_protocol_data : int -> bool -> contents
 val get_op_header : Block_hash.t -> operation_header
 val make_sourced_operation :
   Operation.shell_header ->
-  Alpha_context.proto_operation *
+  Alpha_context.Operation.contents *
   Helpers_account.t ->
   ((Proto_alpha.Main.operation * Helpers_account.t) * Operation_hash.t) proto_tzresult
 val init :
   shell_header -> Block_hash.t -> Int32.t -> int ->
-  (Alpha_context.proto_operation * Helpers_account.t) list ->
+  (Alpha_context.Operation.contents * Helpers_account.t) list ->
   Context.t -> init_block proto_tzresult
 val init_of_result :
   ?priority:int -> res:result ->
-  ops:(Alpha_context.proto_operation * Helpers_account.t) list ->
+  ops:(Alpha_context.Operation.contents * Helpers_account.t) list ->
   init_block proto_tzresult
 val get_level : string option -> int32
 val get_header_hash :
@@ -64,11 +65,11 @@ val begin_construction_pre :
 val make : init_block -> result proto_tzresult Lwt.t
 val make_init :
   shell_header -> Block_hash.t -> Int32.t -> int ->
-  (Alpha_context.proto_operation * Helpers_account.t) list ->
+  (Alpha_context.Operation.contents * Helpers_account.t) list ->
   Context.t -> result proto_tzresult Lwt.t
 val of_res :
   ?priority:int ->
-  ?ops:(Alpha_context.proto_operation * Helpers_account.t) list ->
+  ?ops:(Alpha_context.Operation.contents * Helpers_account.t) list ->
   res:result ->
   unit -> result proto_tzresult Lwt.t
 val endorsement :
diff --git a/src/proto_alpha/lib_protocol/test/helpers/helpers_init.ml b/src/proto_alpha/lib_protocol/test/helpers/helpers_init.ml
index 0d7072231..78acc2902 100644
--- a/src/proto_alpha/lib_protocol/test/helpers/helpers_init.ml
+++ b/src/proto_alpha/lib_protocol/test/helpers/helpers_init.ml
@@ -76,7 +76,7 @@ let main () =
   } in
   let protocol_data =
     Data_encoding.Binary.to_bytes_exn
-      Alpha_context.Block_header.protocol_data_encoding
+      Alpha_context.Block_header.contents_encoding
       (Helpers_block.get_protocol_data 0 true) in
   let tezos_header = { Block_header.shell = header ; protocol_data } in
   Proto_alpha.init context header >>=? fun validation ->
diff --git a/src/proto_alpha/lib_protocol/test/helpers/helpers_operation.ml b/src/proto_alpha/lib_protocol/test/helpers/helpers_operation.ml
index 524a7d2cc..8aa8c37a8 100644
--- a/src/proto_alpha/lib_protocol/test/helpers/helpers_operation.ml
+++ b/src/proto_alpha/lib_protocol/test/helpers/helpers_operation.ml
@@ -108,27 +108,39 @@ let sign src oph protop =
         Some Signature.Endorsement
     | _ ->
         Some Generic_operation in
-  let bytes = Operation.forge oph protop in
-  match src with
-  | None -> bytes, None
-  | Some src ->
-      let signature =
-        Signature.sign ?watermark src.Helpers_account.ppk bytes in
-      Signature.concat bytes signature, Some signature
+  let signature =
+    match src with
+    | None -> None
+    | Some src ->
+        let contents =
+          Data_encoding.Binary.to_bytes_exn
+            Operation.unsigned_encoding (oph, protop) in
+        Some (Signature.sign ?watermark src.Helpers_account.ppk contents) in
+  let proto_bytes =
+    Data_encoding.Binary.to_bytes_exn
+      Operation.protocol_data_encoding
+      { contents = protop ; signature } in
+  (proto_bytes, signature)
 
 let main_of_proto (src: Helpers_account.t) operation_header protocol_operation =
   let (proto,_) = sign (Some src) operation_header protocol_operation in
   let data_operation: Tezos_base.Operation.t =
     {shell = operation_header ; proto} in
   let hash = Tezos_base.Operation.hash data_operation in
-  Proto_alpha.Main.parse_operation hash data_operation >>? fun op ->
-  ok (op, hash)
+  match Data_encoding.Binary.of_bytes
+          Operation.protocol_data_encoding proto with
+  | None ->
+      Error []
+  | Some op ->
+      ok ({ shell = operation_header ; protocol_data = op }, hash)
 
 let apply_of_proto
     (source: Helpers_account.t option) operation_header protocol_operation =
   let (_proto, signature) = sign source operation_header protocol_operation in
   {
     shell = operation_header ;
-    contents = protocol_operation ;
-    signature
+    protocol_data = {
+      contents = protocol_operation ;
+      signature
+    }
   }
diff --git a/src/proto_alpha/lib_protocol/test/helpers/helpers_operation.mli b/src/proto_alpha/lib_protocol/test/helpers/helpers_operation.mli
index 4d06a02b9..5848997e9 100644
--- a/src/proto_alpha/lib_protocol/test/helpers/helpers_operation.mli
+++ b/src/proto_alpha/lib_protocol/test/helpers/helpers_operation.mli
@@ -12,7 +12,7 @@ open Alpha_context
 
 (** Functions building operations *)
 
-val sourced : sourced_operation -> proto_operation
+val sourced : sourced_operation -> Operation.contents
 
 val manager :
   Helpers_account.t -> ?fee:Tez.tez -> manager_operation list ->
@@ -20,7 +20,7 @@ val manager :
 
 val manager_full :
   Helpers_account.t -> ?fee:Tez.tez -> manager_operation list ->
-  Alpha_environment.Context.t -> Z.t -> proto_operation proto_tzresult Lwt.t
+  Alpha_environment.Context.t -> Z.t -> Operation.contents proto_tzresult Lwt.t
 
 val transaction :
   ?parameters:Script.expr -> Tez.t -> Contract.contract ->
@@ -34,20 +34,20 @@ val delegation : public_key_hash -> manager_operation
 
 val delegation_full :
   ?fee:Tez.tez -> Helpers_account.t -> public_key_hash -> Alpha_environment.Context.t ->
-  proto_operation proto_tzresult Lwt.t
+  Operation.contents proto_tzresult Lwt.t
 
 val script_origination_full :
   Script.t option -> Helpers_account.t -> Tez.t -> Z.t -> Alpha_environment.Context.t ->
-  proto_operation proto_tzresult  Lwt.t
+  Operation.contents proto_tzresult  Lwt.t
 
 val origination_full :
   ?spendable:bool -> ?delegatable:bool -> ?fee:Tez.tez ->
   Helpers_account.t -> Tez.t -> Z.t -> Alpha_environment.Context.t ->
-  proto_operation proto_tzresult Lwt.t
+  Operation.contents proto_tzresult Lwt.t
 
 val transaction_full :
   ?fee:Tez.tez -> ?parameters:Proto_alpha.Alpha_context.Script.expr -> Helpers_account.t -> Contract.contract -> Tez.t -> Z.t ->
-  Alpha_environment.Context.t -> proto_operation proto_tzresult Lwt.t
+  Alpha_environment.Context.t -> Operation.contents proto_tzresult Lwt.t
 
 val amendment_operation :
   Helpers_account.t -> amendment_operation -> sourced_operation
@@ -56,16 +56,16 @@ val endorsements :
   ?slot:int -> Block_hash.t -> Raw_level.t -> consensus_operation
 
 val endorsement_full :
-  ?slot:int -> Block_hash.t -> Raw_level.t -> proto_operation
+  ?slot:int -> Block_hash.t -> Raw_level.t -> Operation.contents
 
 val sign :
   Helpers_account.t option -> Tezos_base.Operation.shell_header ->
-  proto_operation -> MBytes.t * Signature.t option
+  Operation.contents -> MBytes.t * Signature.t option
 
 val main_of_proto :
   Helpers_account.t -> Tezos_base.Operation.shell_header ->
-  proto_operation -> (Main.operation * Operation_hash.t) proto_tzresult
+  Operation.contents -> (Main.operation * Operation_hash.t) proto_tzresult
 
 val apply_of_proto :
   Helpers_account.t option -> Tezos_base.Operation.shell_header ->
-  proto_operation -> operation
+  Operation.contents -> operation
diff --git a/src/proto_demo/lib_protocol/src/main.ml b/src/proto_demo/lib_protocol/src/main.ml
index 63b354ea8..a587e4ce6 100644
--- a/src/proto_demo/lib_protocol/src/main.ml
+++ b/src/proto_demo/lib_protocol/src/main.ml
@@ -7,15 +7,27 @@
 (*                                                                        *)
 (**************************************************************************)
 
-type operation = Operation_hash.t
+
+type block_header_data = MBytes.t
+type block_header = {
+  shell : Block_header.shell_header ;
+  protocol_data : block_header_data ;
+}
+let block_header_data_encoding =
+  Data_encoding.(obj1 (req "random_data" Variable.bytes))
+
+type operation_data = unit
+type operation = {
+  shell : Operation.shell_header ;
+  protocol_data : operation_data ;
+}
+let operation_data_encoding = Data_encoding.unit
 let max_operation_data_length = 42
 
 let max_block_length = 42
 let validation_passes = []
 let acceptable_passes _op = []
 
-let parse_operation h _ = Ok h
-
 let compare_operations _ _ = 0
 
 type validation_state = {
@@ -57,16 +69,16 @@ end
 let precheck_block
     ~ancestor_context:_
     ~ancestor_timestamp:_
-    raw_block =
-  Fitness.to_int64 raw_block.Block_header.shell.fitness >>=? fun _ ->
+    (raw_block: block_header) =
+  Fitness.to_int64 raw_block.shell.fitness >>=? fun _ ->
   return ()
 
 let begin_application
     ~predecessor_context:context
     ~predecessor_timestamp:_
     ~predecessor_fitness:_
-    raw_block =
-  Fitness.to_int64 raw_block.Block_header.shell.fitness >>=? fun fitness ->
+    (raw_block: block_header) =
+  Fitness.to_int64 raw_block.shell.fitness >>=? fun fitness ->
   return { context ; fitness }
 
 let begin_construction
diff --git a/src/proto_demo/lib_protocol/src/main.mli b/src/proto_demo/lib_protocol/src/main.mli
new file mode 100644
index 000000000..97caad017
--- /dev/null
+++ b/src/proto_demo/lib_protocol/src/main.mli
@@ -0,0 +1,12 @@
+(**************************************************************************)
+(*                                                                        *)
+(*    Copyright (c) 2014 - 2018.                                          *)
+(*    Dynamic Ledger Solutions, Inc. <contact@tezos.com>                  *)
+(*                                                                        *)
+(*    All rights reserved. No warranty, explicit or implicit, provided.   *)
+(*                                                                        *)
+(**************************************************************************)
+
+(** Tezos Protocol Implementation - Protocol Signature Instance *)
+
+include Updater.PROTOCOL with type block_header_data = MBytes.t
diff --git a/src/proto_genesis/lib_client/client_proto_main.ml b/src/proto_genesis/lib_client/client_proto_main.ml
index 971aa14f2..bb2f90b8c 100644
--- a/src/proto_genesis/lib_client/client_proto_main.ml
+++ b/src/proto_genesis/lib_client/client_proto_main.ml
@@ -14,13 +14,14 @@ let protocol =
     "ProtoGenesisGenesisGenesisGenesisGenesisGenesk612im"
 
 let bake cctxt ?(timestamp = Time.now ()) block command sk =
-  let protocol_data = Data_encoding.Binary.to_bytes_exn Data.Command.encoding command in
+  let protocol_data =
+    Data_encoding.Binary.to_bytes_exn
+      Proto_genesis.block_header_data_encoding
+      { command ; signature = Signature.zero } in
   Block_services.preapply
     cctxt block ~timestamp ~protocol_data
     [] >>=? fun { shell_header } ->
-  let blk =
-    Data_encoding.Binary.to_bytes_exn Block_header.encoding
-      { shell = shell_header ; protocol_data } in
+  let blk = Data.Command.forge shell_header command in
   Client_keys.append sk blk >>=? fun signed_blk ->
   Shell_services.inject_block cctxt signed_blk []
 
diff --git a/src/proto_genesis/lib_protocol/src/main.ml b/src/proto_genesis/lib_protocol/src/main.ml
index 40561e427..2f90c226d 100644
--- a/src/proto_genesis/lib_protocol/src/main.ml
+++ b/src/proto_genesis/lib_protocol/src/main.ml
@@ -32,17 +32,31 @@ let () =
     (function Invalid_signature -> Some () | _ -> None)
     (fun () -> Invalid_signature)
 
-type operation = unit
-let parse_operation _h _op = Error []
+type operation_data = unit
+type operation = {
+  shell: Operation.shell_header ;
+  protocol_data: operation_data ;
+}
+let operation_data_encoding = Data_encoding.unit
+
 let acceptable_passes _op = []
 let compare_operations _ _ = 0
 let validation_passes = []
 
-type block = {
-  shell: Block_header.shell_header ;
+type block_header_data = {
   command: Data.Command.t ;
   signature: Signature.t ;
 }
+type block_header = {
+  shell: Block_header.shell_header ;
+  protocol_data: block_header_data ;
+}
+
+let block_header_data_encoding =
+  Data_encoding.conv
+    (fun { command ; signature } -> (command, signature))
+    (fun (command, signature) ->  { command ; signature })
+    Data.Command.signed_encoding
 
 let max_block_length =
   Data_encoding.Binary.length
@@ -51,14 +65,7 @@ let max_block_length =
                           delay = 0L })
   + Signature.size
 
-let parse_block { Block_header.shell ; protocol_data } : block tzresult =
-  match
-    Data_encoding.Binary.of_bytes Data.Command.signed_encoding protocol_data
-  with
-  | None -> Error [Parsing_error]
-  | Some (command, signature) -> Ok { shell ; command ; signature }
-
-let check_signature ctxt { shell ; command ; signature } =
+let check_signature ctxt { shell ; protocol_data = { command ; signature } } =
   let bytes = Data.Command.forge shell command in
   Data.Pubkey.get_pubkey ctxt >>= fun public_key ->
   fail_unless
@@ -73,8 +80,7 @@ let current_context ({ context ; _ } : validation_state) =
 let precheck_block
     ~ancestor_context:_
     ~ancestor_timestamp:_
-    raw_block =
-  Lwt.return (parse_block raw_block) >>=? fun _ ->
+    _block_header =
   return ()
 
 (* temporary hardcoded key to be removed... *)
@@ -106,12 +112,11 @@ let begin_application
     ~predecessor_context:ctxt
     ~predecessor_timestamp:_
     ~predecessor_fitness:_
-    raw_block =
+    block_header =
   Data.Init.check_inited ctxt >>=? fun () ->
-  Lwt.return (parse_block raw_block) >>=? fun block ->
-  check_signature ctxt block >>=? fun () ->
-  prepare_application ctxt block.command
-    block.shell.level block.shell.timestamp block.shell.fitness
+  check_signature ctxt block_header >>=? fun () ->
+  prepare_application ctxt block_header.protocol_data.command
+    block_header.shell.level block_header.shell.timestamp block_header.shell.fitness
 
 let begin_construction
     ~predecessor_context:ctxt
@@ -130,12 +135,9 @@ let begin_construction
                max_operation_data_length = 0 ;
                last_allowed_fork_level = 0l ;
              }
-  | Some command ->
-      match Data_encoding.Binary.of_bytes Data.Command.encoding command with
-      | None -> failwith "Failed to parse proto header"
-      | Some command ->
-          Data.Init.check_inited ctxt >>=? fun () ->
-          prepare_application ctxt command level timestamp fitness
+  | Some { command ; _ }->
+      Data.Init.check_inited ctxt >>=? fun () ->
+      prepare_application ctxt command level timestamp fitness
 
 let apply_operation _vctxt _ =
   Lwt.return (Error []) (* absurd *)
diff --git a/src/proto_genesis/lib_protocol/src/main.mli b/src/proto_genesis/lib_protocol/src/main.mli
index 731dab063..42cf4c6f7 100644
--- a/src/proto_genesis/lib_protocol/src/main.mli
+++ b/src/proto_genesis/lib_protocol/src/main.mli
@@ -9,4 +9,9 @@
 
 (** Tezos Protocol Implementation - Protocol Signature Instance *)
 
-include Updater.PROTOCOL
+type block_header_data = {
+  command: Data.Command.t ;
+  signature: Signature.t ;
+}
+
+include Updater.PROTOCOL with type block_header_data := block_header_data