diff --git a/src/proto_alpha/lib_protocol/alpha_context.mli b/src/proto_alpha/lib_protocol/alpha_context.mli
index b5c611f4f3c528363604cf2d672c0a151628e7e2..757c90ed3f70f35c008c099082ae26ddab96d48e 100644
--- a/src/proto_alpha/lib_protocol/alpha_context.mli
+++ b/src/proto_alpha/lib_protocol/alpha_context.mli
@@ -3095,7 +3095,9 @@ module Dal : sig
   module Slots_history : sig
     type t
 
-    type hash
+    module Pointer_hash : S.HASH
+
+    type hash = Pointer_hash.t
 
     (* FIXME/DAL: https://gitlab.com/tezos/tezos/-/issues/3766
        Do we need to export this? *)
@@ -3368,7 +3370,18 @@ module Sc_rollup : sig
   val pp_input_request : Format.formatter -> input_request -> unit
 
   module Inbox : sig
-    type t
+    module Skip_list : Skip_list_repr.S
+
+    module Hash : S.HASH
+
+    type level_proof = {
+      hash : Inbox_merkelized_payload_hashes.Hash.t;
+      level : Raw_level.t;
+    }
+
+    type history_proof = (level_proof, Hash.t) Skip_list.cell
+
+    type t = {level : Raw_level.t; old_levels_messages : history_proof}
 
     val pp : Format.formatter -> t -> unit
 
@@ -3378,15 +3391,15 @@ module Sc_rollup : sig
 
     val inbox_level : t -> Raw_level.t
 
-    type history_proof
-
     val old_levels_messages : t -> history_proof
 
     val equal_history_proof : history_proof -> history_proof -> bool
 
     val pp_history_proof : Format.formatter -> history_proof -> unit
 
-    module Hash : S.HASH
+    val hash : t -> Hash.t
+
+    val current_witness : t -> Inbox_merkelized_payload_hashes.Hash.t
 
     module History :
       Bounded_history_repr.S
diff --git a/src/proto_alpha/lib_protocol/dal_slot_repr.mli b/src/proto_alpha/lib_protocol/dal_slot_repr.mli
index 443a14ae05a3f825c41c161653869098e7b8dab4..565135e86cd6bf599061c2e46f8fbb49aa13a807 100644
--- a/src/proto_alpha/lib_protocol/dal_slot_repr.mli
+++ b/src/proto_alpha/lib_protocol/dal_slot_repr.mli
@@ -204,8 +204,10 @@ module History : sig
        confirmed slot headers. *)
   type t
 
+  module Pointer_hash : S.HASH
+
   (** Type of hashes of history. *)
-  type hash
+  type hash = Pointer_hash.t
 
   (** Encoding of the datatype. *)
   val encoding : t Data_encoding.t
diff --git a/src/proto_alpha/lib_protocol/sc_rollup_inbox_repr.ml b/src/proto_alpha/lib_protocol/sc_rollup_inbox_repr.ml
index d82114c7bd9530a7e947f94172297c971da64053..cb5b320707ff43e560d3fc3557378dc423574d0e 100644
--- a/src/proto_alpha/lib_protocol/sc_rollup_inbox_repr.ml
+++ b/src/proto_alpha/lib_protocol/sc_rollup_inbox_repr.ml
@@ -229,10 +229,16 @@ module V1 = struct
       pp_history_proof
       old_levels_messages
 
+  let hash inbox = hash_history_proof inbox.old_levels_messages
+
   let inbox_level inbox = inbox.level
 
   let old_levels_messages inbox = inbox.old_levels_messages
 
+  let current_witness inbox =
+    let {hash; _} = Skip_list.content inbox.old_levels_messages in
+    hash
+
   let encoding =
     Data_encoding.(
       conv
diff --git a/src/proto_alpha/lib_protocol/sc_rollup_inbox_repr.mli b/src/proto_alpha/lib_protocol/sc_rollup_inbox_repr.mli
index 7f6e8c174cd48372c209aa253945129311d5706a..6c000d10d14d208d10cfdfd47c6dd53f1e5cec84 100644
--- a/src/proto_alpha/lib_protocol/sc_rollup_inbox_repr.mli
+++ b/src/proto_alpha/lib_protocol/sc_rollup_inbox_repr.mli
@@ -123,21 +123,13 @@ type error += Inbox_level_reached_messages_limit
 
 module Hash : S.HASH
 
-module V1 : sig
-  (** The type of the inbox for a smart-contract rollup as stored
-    by the protocol in the context. Values that inhabit this type
-    only act as fingerprint for inboxes. *)
-  type t
-
-  val pp : Format.formatter -> t -> unit
-
-  val equal : t -> t -> bool
-
-  val encoding : t Data_encoding.t
+module Skip_list : Skip_list_repr.S
 
-  (** [inbox_level inbox] returns the maximum level of message insertion in
-      [inbox] or its initial level. *)
-  val inbox_level : t -> Raw_level_repr.t
+module V1 : sig
+  type level_proof = {
+    hash : Sc_rollup_inbox_merkelized_payload_hashes_repr.Hash.t;
+    level : Raw_level_repr.t;
+  }
 
   (** A [history_proof] is a [Skip_list.cell] that stores multiple
     hashes. [Skip_list.content history_proof] gives the hash of this cell,
@@ -162,7 +154,27 @@ module V1 : sig
     number of non-empty levels between now and the origination level of
     the rollup.
   *)
-  type history_proof
+  type history_proof = (level_proof, Hash.t) Skip_list.cell
+
+  (** The type of the inbox for a smart-contract rollup as stored
+      by the protocol in the context. Values that inhabit this type
+      only act as fingerprint for inboxes and contain:
+      - [level] : the inbox level ;
+      - [old_levels_messages] : a witness of the inbox history.
+  *)
+  type t = {level : Raw_level_repr.t; old_levels_messages : history_proof}
+
+  val pp : Format.formatter -> t -> unit
+
+  val equal : t -> t -> bool
+
+  val hash : t -> Hash.t
+
+  val encoding : t Data_encoding.t
+
+  (** [inbox_level inbox] returns the maximum level of message insertion in
+      [inbox] or its initial level. *)
+  val inbox_level : t -> Raw_level_repr.t
 
   (** A [History.t] is basically a lookup table of {!history_proof}s. We
       need this if we want to produce inbox proofs because it allows us
@@ -191,12 +203,21 @@ module V1 : sig
   (** [old_levels_messages inbox] returns the latest skip list cell of the inbox
       history that is not up to change (i.e. not the current level tree). *)
   val old_levels_messages : t -> history_proof
+
+  (** [current_witness inbox] returns the current witness of the inbox, i.e. the
+      merkelized payload hash. *)
+  val current_witness :
+    t -> Sc_rollup_inbox_merkelized_payload_hashes_repr.Hash.t
 end
 
 (** Versioning, see {!Sc_rollup_data_version_sig.S} for more information. *)
 include Sc_rollup_data_version_sig.S with type t = V1.t
 
-include module type of V1 with type t = V1.t
+include
+  module type of V1
+    with type level_proof = V1.level_proof
+     and type history_proof = V1.history_proof
+     and type t = V1.t
 
 type serialized_proof