diff --git a/devtools/testnet_experiment_tools/tool_alpha.ml b/devtools/testnet_experiment_tools/tool_alpha.ml
index 2db96ab79bc029c47ceaebff9763a28c7652d4a0..ccc21c83cd537bf53a380780bde8574219dd8cc7 100644
--- a/devtools/testnet_experiment_tools/tool_alpha.ml
+++ b/devtools/testnet_experiment_tools/tool_alpha.ml
@@ -207,7 +207,7 @@ let load_client_context (cctxt : ctxt_kind) =
 
 let get_delegates (cctxt : Protocol_client_context.full) =
   let proj_delegate (alias, public_key_hash, public_key, secret_key_uri) =
-    Baking_state.Consensus_key.make
+    Baking_state.Key.make
       ~alias:(Some alias)
       ~public_key_hash
       ~public_key
@@ -221,8 +221,7 @@ let get_delegates (cctxt : Protocol_client_context.full) =
       cctxt
       (List.filter_map
          (function
-           | {Baking_state.Consensus_key.alias = Some alias; _} -> Some alias
-           | _ -> None)
+           | {Baking_state.Key.alias = Some alias; _} -> Some alias | _ -> None)
          delegates)
   in
   let delegates_no_duplicates = List.sort_uniq compare delegates in
diff --git a/docs/protocols/alpha.rst b/docs/protocols/alpha.rst
index b21e6885be24e10e39ed41a5165b70d2d449ac0a..4a81bd540da9e58266aa7186eecd21082d5a4c49 100644
--- a/docs/protocols/alpha.rst
+++ b/docs/protocols/alpha.rst
@@ -57,6 +57,11 @@ RPC Changes
   a given delegate (``none`` if not yet set), and the list of pending updates to
   that key in the following cycles. (MR :gl:`!17236`)
 
+- Updated ``GET
+  /chains/<chain_id>/blocks/<block_id>/helpers/validators?delegate=<delegate_pkh>&level=<level_id>``
+  with the new field ``companion_key`` which returns the active companion key for
+  the given ``delegate`` and ``level``. (MR :gl:`!17703`)
+
 Operation receipts
 ------------------
 
diff --git a/src/proto_alpha/lib_delegate/baking_actions.ml b/src/proto_alpha/lib_delegate/baking_actions.ml
index b6464b02fc13c4671ac53645c227a06f1fb29cc7..48ca71b4086b17fe653b85db7d9dd30d4b79acd8 100644
--- a/src/proto_alpha/lib_delegate/baking_actions.ml
+++ b/src/proto_alpha/lib_delegate/baking_actions.ml
@@ -247,7 +247,7 @@ let sign_block_header global_state proposer unsigned_block_header =
           (may_sign_block
              cctxt
              block_location
-             ~delegate:proposer.Consensus_key.id
+             ~delegate:proposer.Key.id
              ~level
              ~round [@profiler.record_s {verbosity = Debug} "may sign"])
         in
@@ -964,7 +964,7 @@ let compute_round (proposal : proposal) round_durations =
 let notice_delegates_without_slots all_delegates delegate_slots level =
   let delegates_without_slots =
     List.filter
-      (fun {Baking_state.Consensus_key.id; _} ->
+      (fun {Baking_state.Key.id; _} ->
         not
         @@ List.exists
              (fun ({delegate = {consensus_key; _}; _} : delegate_slot) ->
diff --git a/src/proto_alpha/lib_delegate/baking_commands.ml b/src/proto_alpha/lib_delegate/baking_commands.ml
index 8cb1cbd682297a1c32c143ae49b6dfe0f2d3e542..3bf4630c57d6df3fd51d14e05a7bc53fd2f2b70f 100644
--- a/src/proto_alpha/lib_delegate/baking_commands.ml
+++ b/src/proto_alpha/lib_delegate/baking_commands.ml
@@ -305,7 +305,7 @@ let get_delegates (cctxt : Protocol_client_context.full)
     (pkhs : Signature.public_key_hash list) =
   let open Lwt_result_syntax in
   let proj_delegate (alias, public_key_hash, public_key, secret_key_uri) =
-    Baking_state.Consensus_key.make
+    Baking_state.Key.make
       ~alias:(Some alias)
       ~public_key_hash
       ~public_key
@@ -328,8 +328,7 @@ let get_delegates (cctxt : Protocol_client_context.full)
       cctxt
       (List.filter_map
          (function
-           | {Baking_state.Consensus_key.alias = Some alias; _} -> Some alias
-           | _ -> None)
+           | {Baking_state.Key.alias = Some alias; _} -> Some alias | _ -> None)
          delegates)
   in
   let delegates_no_duplicates = List.sort_uniq compare delegates in
diff --git a/src/proto_alpha/lib_delegate/baking_events.ml b/src/proto_alpha/lib_delegate/baking_events.ml
index b96204b7fbff80bd277e4c43ba891fc13f4353cf..1a64645fafd29ef936b61deb81f3896e9276a1ed 100644
--- a/src/proto_alpha/lib_delegate/baking_events.ml
+++ b/src/proto_alpha/lib_delegate/baking_events.ml
@@ -604,13 +604,11 @@ module Delegates = struct
         Format.fprintf
           ppf
           "@[<v 2>@,%a@]"
-          Format.(
-            pp_print_list ~pp_sep:pp_print_cut Baking_state.Consensus_key.pp)
+          Format.(pp_print_list ~pp_sep:pp_print_cut Baking_state.Key.pp)
           delegates)
       ( "delegates",
         Data_encoding.list
-          Baking_state.Consensus_key
-          .consensus_key_without_sk_encoding__cannot_decode )
+          Baking_state.Key.consensus_key_without_sk_encoding__cannot_decode )
 end
 
 module Scheduling = struct
@@ -1126,8 +1124,8 @@ module Actions = struct
       ~msg:
         "The following delegates have no attesting rights at level {level}: \
          {delegates}"
-      ~pp1:(Format.pp_print_list Baking_state.Consensus_key.pp)
-      ("delegates", Data_encoding.list Baking_state.Consensus_key.encoding)
+      ~pp1:(Format.pp_print_list Baking_state.Key.pp)
+      ("delegates", Data_encoding.list Baking_state.Key.encoding)
       ~pp2:pp_int32
       ("level", Data_encoding.int32)
 
diff --git a/src/proto_alpha/lib_delegate/baking_highwatermarks.ml b/src/proto_alpha/lib_delegate/baking_highwatermarks.ml
index 4c9824b6ca9f947d8624cbfe56a28e2e1e3a16a6..55a76f0e43c22c4f27505762f9564be00e4542e9 100644
--- a/src/proto_alpha/lib_delegate/baking_highwatermarks.ml
+++ b/src/proto_alpha/lib_delegate/baking_highwatermarks.ml
@@ -99,9 +99,9 @@ let () =
     (fun highwatermark -> Block_previously_attested highwatermark)
 
 module DelegateMap = Map.Make (struct
-  type t = Baking_state.Consensus_key_id.t
+  type t = Baking_state.Key_id.t
 
-  let compare = Baking_state.Consensus_key_id.compare
+  let compare = Baking_state.Key_id.compare
 end)
 
 let highwatermark_delegate_map_encoding =
@@ -112,7 +112,7 @@ let highwatermark_delegate_map_encoding =
       fun l -> List.fold_left (fun map (k, v) -> add k v map) empty l)
     (list
        (obj2
-          (req "delegate" Baking_state.Consensus_key_id.encoding)
+          (req "delegate" Baking_state.Key_id.encoding)
           (req "highwatermark" highwatermark_encoding)))
 
 type highwatermarks = {
diff --git a/src/proto_alpha/lib_delegate/baking_highwatermarks.mli b/src/proto_alpha/lib_delegate/baking_highwatermarks.mli
index cfc15b69accce94e45c692e499ac8a1feb8c531d..26b9f4acfbcb8bec990653fe0384f5f80ea1558d 100644
--- a/src/proto_alpha/lib_delegate/baking_highwatermarks.mli
+++ b/src/proto_alpha/lib_delegate/baking_highwatermarks.mli
@@ -43,29 +43,21 @@ val load :
 val may_sign_block :
   #Protocol_client_context.full ->
   [`Highwatermarks] Baking_files.location ->
-  delegate:Baking_state.Consensus_key_id.t ->
+  delegate:Baking_state.Key_id.t ->
   level:int32 ->
   round:Round.t ->
   bool tzresult Lwt.t
 
 val may_sign_preattestation :
-  t ->
-  delegate:Baking_state.Consensus_key_id.t ->
-  level:int32 ->
-  round:Round.t ->
-  bool
+  t -> delegate:Baking_state.Key_id.t -> level:int32 -> round:Round.t -> bool
 
 val may_sign_attestation :
-  t ->
-  delegate:Baking_state.Consensus_key_id.t ->
-  level:int32 ->
-  round:Round.t ->
-  bool
+  t -> delegate:Baking_state.Key_id.t -> level:int32 -> round:Round.t -> bool
 
 val record_block :
   #Protocol_client_context.full ->
   [`Highwatermarks] Baking_files.location ->
-  delegate:Baking_state.Consensus_key_id.t ->
+  delegate:Baking_state.Key_id.t ->
   level:int32 ->
   round:Round.t ->
   unit tzresult Lwt.t
@@ -73,7 +65,7 @@ val record_block :
 val record_preattestation :
   #Protocol_client_context.full ->
   [`Highwatermarks] Baking_files.location ->
-  delegate:Baking_state.Consensus_key_id.t ->
+  delegate:Baking_state.Key_id.t ->
   level:int32 ->
   round:Round.t ->
   unit tzresult Lwt.t
@@ -81,7 +73,7 @@ val record_preattestation :
 val record_attestation :
   #Protocol_client_context.full ->
   [`Highwatermarks] Baking_files.location ->
-  delegate:Baking_state.Consensus_key_id.t ->
+  delegate:Baking_state.Key_id.t ->
   level:int32 ->
   round:Round.t ->
   unit tzresult Lwt.t
@@ -90,7 +82,7 @@ val record_all_preattestations :
   t ->
   #Protocol_client_context.full ->
   [`Highwatermarks] Baking_files.location ->
-  delegates:Baking_state.Consensus_key_id.t list ->
+  delegates:Baking_state.Key_id.t list ->
   level:int32 ->
   round:Round.t ->
   unit tzresult Lwt.t
@@ -99,7 +91,7 @@ val record_all_attestations :
   t ->
   #Protocol_client_context.full ->
   [`Highwatermarks] Baking_files.location ->
-  delegates:Baking_state.Consensus_key_id.t list ->
+  delegates:Baking_state.Key_id.t list ->
   level:int32 ->
   round:Round.t ->
   unit tzresult Lwt.t
diff --git a/src/proto_alpha/lib_delegate/baking_lib.mli b/src/proto_alpha/lib_delegate/baking_lib.mli
index 20e2fd4c72c6c1155bbdcd7db76f53a1b072390c..55143721bca7c338039ed2a67eb12788f14dfd22 100644
--- a/src/proto_alpha/lib_delegate/baking_lib.mli
+++ b/src/proto_alpha/lib_delegate/baking_lib.mli
@@ -43,19 +43,19 @@ val bake :
   ?count:int ->
   ?votes:Baking_configuration.per_block_votes_config ->
   ?state_recorder:Baking_configuration.state_recorder_config ->
-  Baking_state.Consensus_key.t list ->
+  Baking_state.Key.t list ->
   unit tzresult Lwt.t
 
 val preattest :
   Protocol_client_context.full ->
   ?force:bool ->
-  Baking_state.Consensus_key.t list ->
+  Baking_state.Key.t list ->
   unit tzresult Lwt.t
 
 val attest :
   Protocol_client_context.full ->
   ?force:bool ->
-  Baking_state.Consensus_key.t list ->
+  Baking_state.Key.t list ->
   unit tzresult Lwt.t
 
 val propose :
@@ -69,7 +69,7 @@ val propose :
   ?extra_operations:Baking_configuration.Operations_source.t ->
   ?context_path:string ->
   ?state_recorder:Baking_configuration.state_recorder_config ->
-  Baking_state.Consensus_key.t list ->
+  Baking_state.Key.t list ->
   unit tzresult Lwt.t
 
 (** [repropose] tries to bake a new block proposal on the same level
@@ -80,5 +80,5 @@ val repropose :
   Protocol_client_context.full ->
   ?force:bool ->
   ?force_round:Round.t ->
-  Baking_state.Consensus_key.t list ->
+  Baking_state.Key.t list ->
   unit tzresult Lwt.t
diff --git a/src/proto_alpha/lib_delegate/baking_nonces.ml b/src/proto_alpha/lib_delegate/baking_nonces.ml
index 7857bb5c071949a4db17a1593a67762ab5c2f2a6..f7e99824a516f158bb9aa70d9e99d20cf452b97d 100644
--- a/src/proto_alpha/lib_delegate/baking_nonces.ml
+++ b/src/proto_alpha/lib_delegate/baking_nonces.ml
@@ -409,7 +409,7 @@ let generate_deterministic_nonce ?timeout secret_key_uri data =
 
 let generate_seed_nonce ?timeout
     (nonce_config : Baking_configuration.nonce_config)
-    (delegate : Baking_state.Consensus_key.t) level =
+    (delegate : Baking_state.Key.t) level =
   let open Lwt_result_syntax in
   let* nonce =
     match nonce_config with
diff --git a/src/proto_alpha/lib_delegate/baking_nonces.mli b/src/proto_alpha/lib_delegate/baking_nonces.mli
index 44c2ac915b9b45a24ebbebc0524710f02a5269b5..bc2e43fd55cefba1376a8a88a2a0414ce9c49d63 100644
--- a/src/proto_alpha/lib_delegate/baking_nonces.mli
+++ b/src/proto_alpha/lib_delegate/baking_nonces.mli
@@ -48,7 +48,7 @@ val load :
 val generate_seed_nonce :
   ?timeout:float ->
   Baking_configuration.nonce_config ->
-  Baking_state.Consensus_key.t ->
+  Baking_state.Key.t ->
   Raw_level.t ->
   (Nonce_hash.t * Nonce.t) tzresult Lwt.t
 
diff --git a/src/proto_alpha/lib_delegate/baking_scheduling.ml b/src/proto_alpha/lib_delegate/baking_scheduling.ml
index 6d9c017d813936b4f5cf106396203efc7a48c9fa..803e35d1c65ca800454c7213b346f9c8466caf80 100644
--- a/src/proto_alpha/lib_delegate/baking_scheduling.ml
+++ b/src/proto_alpha/lib_delegate/baking_scheduling.ml
@@ -897,7 +897,7 @@ let retry (cctxt : #Protocol_client_context.full) ?max_delay ~delay ~factor
 let try_resolve_consensus_keys cctxt key =
   let open Lwt_syntax in
   let levels_to_inspect = 50 in
-  let pkh = Consensus_key_id.to_pkh key.Consensus_key.id in
+  let pkh = Key_id.to_pkh key.Key.id in
   let* res =
     Plugin.Alpha_services.Delegate.deactivated cctxt (`Main, `Head 0) pkh
   in
@@ -923,7 +923,13 @@ let try_resolve_consensus_keys cctxt key =
           | Error _ | Ok [] -> try_find_delegate_key (head_offset - 1)
           | Ok
               (Plugin.RPC.Validators.
-                 {delegate; level = _; consensus_key = _; slots = _}
+                 {
+                   delegate;
+                   level = _;
+                   consensus_key = _;
+                   companion_key = _;
+                   slots = _;
+                 }
               :: _) ->
               (* The primary registered key as delegate found. Return it. *)
               return delegate
diff --git a/src/proto_alpha/lib_delegate/baking_scheduling.mli b/src/proto_alpha/lib_delegate/baking_scheduling.mli
index b6f52af181ca3bdf1f0652d6420743cc283c2da9..8d46c9a6cd78a710006ece12e08e3ae5b435d04e 100644
--- a/src/proto_alpha/lib_delegate/baking_scheduling.mli
+++ b/src/proto_alpha/lib_delegate/baking_scheduling.mli
@@ -81,7 +81,7 @@ val run :
   ?constants:Constants.t ->
   chain:Chain_services.chain ->
   Baking_configuration.t ->
-  Baking_state.Consensus_key.t list ->
+  Baking_state.Key.t list ->
   unit tzresult Lwt.t
 
 (** {2 Functions only needed for the baking_lib} *)
@@ -145,7 +145,7 @@ val create_initial_state :
   Operation_worker.t ->
   current_proposal:proposal ->
   ?constants:Constants.t ->
-  Baking_state.Consensus_key.t list ->
+  Baking_state.Key.t list ->
   state tzresult Lwt.t
 
 (** [automaton_loop ?stop_on_event baking_configuration on_error loop_state
diff --git a/src/proto_alpha/lib_delegate/baking_state.ml b/src/proto_alpha/lib_delegate/baking_state.ml
index 7a0228cd31a31a32724c330aab363781af3a394a..5a10844ea61aee30eb02205e5894d655f1539a67 100644
--- a/src/proto_alpha/lib_delegate/baking_state.ml
+++ b/src/proto_alpha/lib_delegate/baking_state.ml
@@ -29,7 +29,7 @@ open Baking_errors
 
 module Profiler = (val Profiler.wrap Baking_profiler.baker_profiler)
 
-module Consensus_key_id = struct
+module Key_id = struct
   type t = Signature.Public_key_hash.t
 
   let to_pkh pkh = pkh
@@ -43,12 +43,12 @@ module Consensus_key_id = struct
   module Table = Signature.Public_key_hash.Table
 end
 
-module Consensus_key = struct
+module Key = struct
   (** A consensus key (aka, a validator) is identified by its alias name, its
     public key, its public key hash, and its secret key. *)
   type t = {
     alias : string option;
-    id : Consensus_key_id.t;
+    id : Key_id.t;
     public_key : Signature.Public_key.t;
     secret_key_uri : Client_keys.sk_uri;
   }
@@ -110,26 +110,40 @@ module Delegate_id = struct
 end
 
 module Delegate = struct
-  type t = {consensus_key : Consensus_key.t; delegate_id : Delegate_id.t}
+  type t = {
+    consensus_key : Key.t;
+    companion_key : Key.t option;
+    delegate_id : Delegate_id.t;
+  }
 
   let encoding =
     let open Data_encoding in
     conv
-      (fun {consensus_key; delegate_id} -> (consensus_key, delegate_id))
-      (fun (consensus_key, delegate_id) -> {consensus_key; delegate_id})
-      (merge_objs
-         Consensus_key.encoding
-         (obj1 (req "delegate" Delegate_id.encoding)))
-
-  let pp fmt {consensus_key; delegate_id} =
+      (fun {consensus_key; companion_key; delegate_id} ->
+        (consensus_key, delegate_id, companion_key))
+      (fun (consensus_key, delegate_id, companion_key) ->
+        {consensus_key; delegate_id; companion_key})
+      (obj3
+         (req "consensus_key" Key.encoding)
+         (req "delegate" Delegate_id.encoding)
+         (opt "companion_key" Key.encoding))
+
+  let pp fmt {consensus_key; delegate_id; companion_key} =
+    let str_companion_key =
+      match companion_key with
+      | Some companion_key ->
+          Format.asprintf " with companion key %a" Key.pp companion_key
+      | None -> ""
+    in
     if Signature.Public_key_hash.equal consensus_key.id delegate_id then
-      Consensus_key.pp fmt consensus_key
+      Format.fprintf fmt "%a%s" Key.pp consensus_key str_companion_key
     else
       Format.fprintf
         fmt
-        "%a@,on behalf of %a"
-        Consensus_key.pp
+        "%a%s@,on behalf of %a"
+        Key.pp
         consensus_key
+        str_companion_key
         Delegate_id.pp
         delegate_id
 end
@@ -642,7 +656,7 @@ type global_state = {
   (* the validation mode used by the baker*)
   validation_mode : validation_mode;
   (* the delegates on behalf of which the baker is running *)
-  delegates : Consensus_key.t list;
+  delegates : Key.t list;
   cache : cache;
   dal_node_rpc_ctxt : Tezos_rpc.Context.generic option;
 }
@@ -1059,9 +1073,9 @@ let may_load_attestable_data state =
 
 module DelegateSet = struct
   include Set.Make (struct
-    type t = Consensus_key.t
+    type t = Key.t
 
-    let compare Consensus_key.{id = pkh; _} Consensus_key.{id = pkh'; _} =
+    let compare Key.{id = pkh; _} Key.{id = pkh'; _} =
       Signature.Public_key_hash.compare pkh pkh'
   end)
 
@@ -1082,16 +1096,29 @@ let delegate_slots attesting_rights delegates =
   let own_delegate_first_slots, own_delegate_slots, all_delegate_voting_power =
     List.fold_left
       (fun (own_list, own_map, all_map) slot ->
-        let {Plugin.RPC.Validators.consensus_key; delegate; slots; _} = slot in
+        let {
+          Plugin.RPC.Validators.consensus_key;
+          companion_key;
+          delegate;
+          slots;
+          level = _;
+        } =
+          slot
+        in
         let first_slot = Stdlib.List.hd slots in
         let attesting_power = List.length slots in
         let all_map = SlotMap.add first_slot attesting_power all_map in
         let own_list, own_map =
           match DelegateSet.find_pkh consensus_key own_delegates with
           | Some consensus_key ->
+              let companion_key =
+                Option.bind companion_key (fun companion_key ->
+                    DelegateSet.find_pkh (Bls companion_key) own_delegates)
+              in
               let attesting_slot =
                 {
-                  delegate = {consensus_key; delegate_id = delegate};
+                  delegate =
+                    {consensus_key; delegate_id = delegate; companion_key};
                   first_slot;
                   attesting_power;
                 }
@@ -1217,7 +1244,7 @@ let pp_global_state fmt {chain_id; config; validation_mode; delegates; _} =
     config
     pp_validation_mode
     validation_mode
-    Format.(pp_print_list Consensus_key.pp)
+    Format.(pp_print_list Key.pp)
     delegates
 
 let pp_option pp fmt = function
diff --git a/src/proto_alpha/lib_delegate/baking_state.mli b/src/proto_alpha/lib_delegate/baking_state.mli
index 6dd99f47911fdab84eb64c0a52e32a4cae3c67bb..e38bb6b5384779ed08e33628ec808ccbd23f8e84 100644
--- a/src/proto_alpha/lib_delegate/baking_state.mli
+++ b/src/proto_alpha/lib_delegate/baking_state.mli
@@ -26,8 +26,10 @@
 open Protocol
 open Alpha_context
 
-(** {2 Consensus key type and functions} *)
-module Consensus_key_id : sig
+(** {2 Key type and functions}
+
+    Used for both consensus keys and companion keys. *)
+module Key_id : sig
   type t
 
   (** Only use at library frontiers *)
@@ -46,10 +48,10 @@ module Consensus_key_id : sig
   end
 end
 
-module Consensus_key : sig
+module Key : sig
   type t = private {
     alias : string option;
-    id : Consensus_key_id.t;
+    id : Key_id.t;
     public_key : Signature.public_key;
     secret_key_uri : Client_keys.sk_uri;
   }
@@ -89,7 +91,11 @@ module Delegate_id : sig
 end
 
 module Delegate : sig
-  type t = {consensus_key : Consensus_key.t; delegate_id : Delegate_id.t}
+  type t = {
+    consensus_key : Key.t;
+    companion_key : Key.t option;
+    delegate_id : Delegate_id.t;
+  }
 
   val encoding : t Data_encoding.t
 
@@ -145,7 +151,7 @@ val compute_delegate_slots :
   ?block:Block_services.block ->
   level:int32 ->
   chain:Shell_services.chain ->
-  Consensus_key.t list ->
+  Key.t list ->
   delegate_slots tzresult Lwt.t
 
 (** {2 Consensus operations types functions} *)
@@ -503,7 +509,7 @@ type global_state = {
   operation_worker : Operation_worker.t;
   mutable forge_worker_hooks : forge_worker_hooks;
   validation_mode : validation_mode;
-  delegates : Consensus_key.t list;
+  delegates : Key.t list;
   cache : cache;
   dal_node_rpc_ctxt : Tezos_rpc.Context.generic option;
 }
diff --git a/src/proto_alpha/lib_delegate/client_daemon.mli b/src/proto_alpha/lib_delegate/client_daemon.mli
index b0073a38c7892f4d57c8d215945334b02b87db16..70116a30cd318f85bc2764596f6fc863d7226000 100644
--- a/src/proto_alpha/lib_delegate/client_daemon.mli
+++ b/src/proto_alpha/lib_delegate/client_daemon.mli
@@ -42,7 +42,7 @@ module Baker : sig
     ?state_recorder:Baking_configuration.state_recorder_config ->
     chain:Shell_services.chain ->
     keep_alive:bool ->
-    Baking_state.Consensus_key.t list ->
+    Baking_state.Key.t list ->
     unit tzresult Lwt.t
 end
 
diff --git a/src/proto_alpha/lib_delegate/forge_worker.ml b/src/proto_alpha/lib_delegate/forge_worker.ml
index 8f61f91647fc68a5272589ceef08dbab09b52c32..fd04a0e3b2da4e3078b07e199fd4fcd37efb0118 100644
--- a/src/proto_alpha/lib_delegate/forge_worker.ml
+++ b/src/proto_alpha/lib_delegate/forge_worker.ml
@@ -70,7 +70,7 @@ type worker = {
   push_task : forge_request option -> unit;
   push_event : forge_event option -> unit;
   event_stream : forge_event Lwt_stream.t;
-  delegate_signing_queues : Delegate_signing_queue.t Consensus_key_id.Table.t;
+  delegate_signing_queues : Delegate_signing_queue.t Key_id.Table.t;
 }
 
 type t = worker
@@ -82,7 +82,7 @@ let get_event_stream state = state.event_stream
 let cancel_all_pending_tasks {delegate_signing_queues; _} =
   Lwt.dont_wait
     (fun () ->
-      Consensus_key_id.Table.iter_p
+      Key_id.Table.iter_p
         (fun _ queue -> Delegate_signing_queue.cancel_pending_tasks queue)
         delegate_signing_queues)
     (fun _exn -> ())
@@ -90,7 +90,7 @@ let cancel_all_pending_tasks {delegate_signing_queues; _} =
 let shutdown state =
   let open Lwt_syntax in
   let* () =
-    Consensus_key_id.Table.iter_p
+    Key_id.Table.iter_p
       (fun _ queue -> Delegate_signing_queue.cancel_all_tasks_and_close queue)
       state.delegate_signing_queues
   in
@@ -99,13 +99,13 @@ let shutdown state =
 
 let get_or_create_queue worker delegate =
   match
-    Consensus_key_id.Table.find_opt
+    Key_id.Table.find_opt
       worker.delegate_signing_queues
       delegate.Baking_state.Delegate.consensus_key.id
   with
   | None ->
       let queue = Delegate_signing_queue.create delegate in
-      Consensus_key_id.Table.add
+      Key_id.Table.add
         worker.delegate_signing_queues
         delegate.consensus_key.id
         queue ;
@@ -189,7 +189,7 @@ let start (baking_state : Baking_state.global_state) =
   let open Lwt_result_syntax in
   let task_stream, push_task = Lwt_stream.create () in
   let event_stream, push_event = Lwt_stream.create () in
-  let delegate_signing_queues = Consensus_key_id.Table.create 13 in
+  let delegate_signing_queues = Key_id.Table.create 13 in
   let state : worker =
     {push_task; push_event; event_stream; delegate_signing_queues}
   in
diff --git a/src/proto_alpha/lib_delegate/test/mockup_simulator/mockup_simulator.ml b/src/proto_alpha/lib_delegate/test/mockup_simulator/mockup_simulator.ml
index eace277cae55d652ea4239e918fca3aaa76915f2..e3c7ea24343a786fabd3d452f3aceba686309e51 100644
--- a/src/proto_alpha/lib_delegate/test/mockup_simulator/mockup_simulator.ml
+++ b/src/proto_alpha/lib_delegate/test/mockup_simulator/mockup_simulator.ml
@@ -149,7 +149,7 @@ module type Hooks = sig
 
   val on_start_baker :
     baker_position:int ->
-    delegates:Baking_state.Consensus_key.t list ->
+    delegates:Baking_state.Key.t list ->
     cctxt:Protocol_client_context.full ->
     unit Lwt.t
 
@@ -935,7 +935,7 @@ class tezt_printer : Tezos_client_base.Client_context.printer =
   end
 
 (** Start baker process. *)
-let baker_process ~(delegates : Baking_state.Consensus_key.t list) ~base_dir
+let baker_process ~(delegates : Baking_state.Key.t list) ~base_dir
     ~(genesis_block : Block_header.t * Tezos_protocol_environment.rpc_context)
     ~i ~global_chain_table ~broadcast_pipes ~(user_hooks : (module Hooks)) =
   let open Lwt_result_syntax in
@@ -965,11 +965,10 @@ let baker_process ~(delegates : Baking_state.Consensus_key.t list) ~base_dir
   let*! () = User_hooks.on_start_baker ~baker_position:i ~delegates ~cctxt in
   let* () =
     List.iter_es
-      (fun ({alias; public_key; id; secret_key_uri} :
-             Baking_state.Consensus_key.t) ->
+      (fun ({alias; public_key; id; secret_key_uri} : Baking_state.Key.t) ->
         let name = alias |> WithExceptions.Option.get ~loc:__LOC__ in
         let* public_key_uri = Client_keys.neuterize secret_key_uri in
-        let pkh = Baking_state.Consensus_key_id.to_pkh id in
+        let pkh = Baking_state.Key_id.to_pkh id in
         Client_keys.register_key
           wallet
           ~force:false
@@ -1288,8 +1287,8 @@ let default_config =
 let make_baking_delegate
     ( (account : Alpha_context.Parameters.bootstrap_account),
       (secret : Tezos_mockup_commands.Mockup_wallet.bootstrap_secret) ) :
-    Baking_state.Consensus_key.t =
-  Baking_state.Consensus_key.make
+    Baking_state.Key.t =
+  Baking_state.Key.make
     ~alias:(Some secret.name)
     ~public_key_hash:account.public_key_hash
     ~public_key:(account.public_key |> WithExceptions.Option.get ~loc:__LOC__)
diff --git a/src/proto_alpha/lib_delegate/test/mockup_simulator/mockup_simulator.mli b/src/proto_alpha/lib_delegate/test/mockup_simulator/mockup_simulator.mli
index 4ce76277e3ad609dd7832dada6cc9b86e1f48425..de18ce2d1236e2622f2451152c73b62244b28ba6 100644
--- a/src/proto_alpha/lib_delegate/test/mockup_simulator/mockup_simulator.mli
+++ b/src/proto_alpha/lib_delegate/test/mockup_simulator/mockup_simulator.mli
@@ -126,7 +126,7 @@ module type Hooks = sig
      bakers that were started for this run. *)
   val on_start_baker :
     baker_position:int ->
-    delegates:Baking_state.Consensus_key.t list ->
+    delegates:Baking_state.Key.t list ->
     cctxt:Protocol_client_context.full ->
     unit Lwt.t
 
diff --git a/src/proto_alpha/lib_plugin/RPC.ml b/src/proto_alpha/lib_plugin/RPC.ml
index 601ea0c9127d9503d5d26a0a84a440841bb31037..4014e166d12a0e2a54e325dd60560c2195b03573 100644
--- a/src/proto_alpha/lib_plugin/RPC.ml
+++ b/src/proto_alpha/lib_plugin/RPC.ml
@@ -3957,21 +3957,23 @@ module Validators = struct
     level : Raw_level.t;
     delegate : Signature.Public_key_hash.t;
     consensus_key : Signature.public_key_hash;
+    companion_key : Bls.Public_key_hash.t option;
     slots : Slot.t list;
   }
 
   let encoding =
     let open Data_encoding in
     conv
-      (fun {level; delegate; consensus_key; slots} ->
-        (level, delegate, slots, consensus_key))
-      (fun (level, delegate, slots, consensus_key) ->
-        {level; delegate; consensus_key; slots})
-      (obj4
+      (fun {level; delegate; consensus_key; companion_key; slots} ->
+        (level, delegate, slots, consensus_key, companion_key))
+      (fun (level, delegate, slots, consensus_key, companion_key) ->
+        {level; delegate; consensus_key; companion_key; slots})
+      (obj5
          (req "level" Raw_level.encoding)
          (req "delegate" Signature.Public_key_hash.encoding)
          (req "slots" (list Slot.encoding))
-         (req "consensus_key" Signature.Public_key_hash.encoding))
+         (req "consensus_key" Signature.Public_key_hash.encoding)
+         (opt "companion_key" Bls.Public_key_hash.encoding))
 
   module S = struct
     open Data_encoding
@@ -4016,8 +4018,9 @@ module Validators = struct
     let+ ctxt, rights = Baking.attesting_rights ctxt level in
     ( ctxt,
       Signature.Public_key_hash.Map.fold
-        (fun _pkh {Baking.delegate; consensus_key; slots} acc ->
-          {level = level.level; delegate; consensus_key; slots} :: acc)
+        (fun _pkh {Baking.delegate; consensus_key; companion_key; slots} acc ->
+          {level = level.level; delegate; consensus_key; companion_key; slots}
+          :: acc)
         rights
         acc )
 
diff --git a/src/proto_alpha/lib_protocol/baking.ml b/src/proto_alpha/lib_protocol/baking.ml
index 0af0632f22b0f4f1db7e2b0fadfd7a8f3d7317dc..3bad0551af7f6ad1d1b93f971e0d2c966eb6b5be 100644
--- a/src/proto_alpha/lib_protocol/baking.ml
+++ b/src/proto_alpha/lib_protocol/baking.ml
@@ -76,6 +76,7 @@ let bonus_baking_reward ctxt ~attestation_power =
 type ordered_slots = {
   delegate : Signature.public_key_hash;
   consensus_key : Signature.public_key_hash;
+  companion_key : Bls.Public_key_hash.t option;
   slots : Slot.t list;
 }
 
@@ -97,6 +98,7 @@ let attesting_rights (ctxt : t) level =
                   {
                     delegate = consensus_pk.delegate;
                     consensus_key = consensus_pk.consensus_pkh;
+                    companion_key = consensus_pk.companion_pkh;
                     slots = [slot];
                   }
             | Some slots -> Some {slots with slots = slot :: slots.slots})
diff --git a/src/proto_alpha/lib_protocol/baking.mli b/src/proto_alpha/lib_protocol/baking.mli
index 0aeabf4f5731ba478fe17c2641597f85881caacf..540ec98a72c9eb09fb9e8085050d015b3e536c03 100644
--- a/src/proto_alpha/lib_protocol/baking.mli
+++ b/src/proto_alpha/lib_protocol/baking.mli
@@ -36,6 +36,7 @@ type error +=
 type ordered_slots = private {
   delegate : Signature.public_key_hash;
   consensus_key : Signature.public_key_hash;
+  companion_key : Bls.Public_key_hash.t option;
   slots : Slot.t list;
 }
 
diff --git a/tezt/lib_tezos/agnostic_baker.ml b/tezt/lib_tezos/agnostic_baker.ml
index 3d1b0d5c7c0283aee184db09d3d43f93aa00052c..c7806187c749813d1bdf97afc61bffe6ce4c6875 100644
--- a/tezt/lib_tezos/agnostic_baker.ml
+++ b/tezt/lib_tezos/agnostic_baker.ml
@@ -328,7 +328,17 @@ let log_block_injection ?color baker =
         let open JSON in
         let level = event.value |-> "level" |> as_int in
         let round = event.value |-> "round" |> as_int in
-        let delegate = event.value |-> "delegate" |-> "alias" |> as_string in
+        let delegate =
+          event.value |-> "delegate" |-> "alias" |> as_string_opt
+        in
+        let delegate =
+          match delegate with
+          | None ->
+              (* The encoding was changed in Protocol 023 *)
+              event.value |-> "delegate" |-> "consensus_key" |-> "alias"
+              |> as_string
+          | Some delegate -> delegate
+        in
         Log.info
           ?color
           "[%s] Block injected at level %d round %d for %s."
diff --git a/tezt/tests/companion_key.ml b/tezt/tests/companion_key.ml
index 1902e7869789fdae1aaf54adabe68b55cc88c19c..43808c870d38456a04328ad1088be2de153976d3 100644
--- a/tezt/tests/companion_key.ml
+++ b/tezt/tests/companion_key.ml
@@ -44,6 +44,31 @@ let companion_key_typ : companion_key Check.typ =
         (active_companion_key, pending_companion_keys))
       (tuple2 (option string) (list (tuple2 int string))))
 
+let get_validators_companion_key ?level (delegate : Account.key) client =
+  let* json =
+    Client.RPC.call client
+    @@ RPC.get_chain_block_helper_validators
+         ?level
+         ~delegate:delegate.public_key_hash
+         ()
+  in
+  let companion_key = JSON.(json |=> 0 |-> "companion_key" |> as_string_opt) in
+  Log.info
+    ~color:Log.Color.FG.green
+    "companion_key = %s"
+    (match companion_key with Some ck -> ck | None -> "None") ;
+  return companion_key
+
+let check_validators_companion_key ~__LOC__ ?level (delegate : Account.key)
+    client ~expected =
+  let* companion_key = get_validators_companion_key ?level delegate client in
+  Check.(
+    (companion_key = expected)
+      (option string)
+      ~__LOC__
+      ~error_msg:"Expected %R, got %L") ;
+  unit
+
 let get_companion_key ?block client (delegate : Account.key) :
     companion_key Lwt.t =
   let* json =
@@ -88,13 +113,7 @@ let check_companion_key ~__LOC__ delegate ?expected_active
       ~error_msg:"Expected %R, got %L") ;
   unit
 
-let test_update_companion_key =
-  Protocol.register_regression_test
-    ~__FILE__
-    ~title:"update companion key"
-    ~tags:[team; "companion_key"]
-    ~supports:(Protocol.From_protocol 023)
-  @@ fun protocol ->
+let init_node_and_client ~protocol =
   let parameters =
     (* we update parameters for faster testing: no need to wait
        2 cycles for the consensus key to activate. *)
@@ -110,10 +129,19 @@ let test_update_companion_key =
   let* parameter_file =
     Protocol.write_parameter_file ~base:(Right (protocol, None)) parameters
   in
-  let* _, client =
+  let* node, client =
     Client.init_with_protocol ~parameter_file ~protocol `Client ()
   in
+  return (node, client)
 
+let test_update_companion_key =
+  Protocol.register_regression_test
+    ~__FILE__
+    ~title:"update companion key"
+    ~tags:[team; "companion_key"]
+    ~supports:(Protocol.From_protocol 023)
+  @@ fun protocol ->
+  let* _node, client = init_node_and_client ~protocol in
   let delegate = Constant.bootstrap1 in
   let* consensus_key_bls =
     Client.gen_and_show_keys ~alias:"consensus_key" ~sig_alg:"bls" client
@@ -158,8 +186,67 @@ let test_update_companion_key =
       ~expected_active:companion_key_bls
       client
   in
+  let* () =
+    check_validators_companion_key ~__LOC__ delegate ~expected:None client
+  in
+  let* current_level = get_current_level client in
+  let* () =
+    check_validators_companion_key
+      ~__LOC__
+      ~level:(current_level.level + 1)
+      delegate
+      ~expected:(Some companion_key_bls.public_key_hash)
+      client
+  in
+  unit
+
+let test_update_companion_key_without_consensus_key =
+  Protocol.register_regression_test
+    ~__FILE__
+    ~title:"update companion key without updating consensus key"
+    ~tags:[team; "companion_key"]
+    ~supports:(Protocol.From_protocol 023)
+  @@ fun protocol ->
+  let* _node, client = init_node_and_client ~protocol in
+  let delegate = Constant.bootstrap1 in
+  let* companion_key_bls =
+    Client.gen_and_show_keys ~alias:"companion_key" ~sig_alg:"bls" client
+  in
+  Log.info "Updating companion key" ;
+  let* () =
+    Client.update_companion_key
+      ~hooks
+      ~src:delegate.alias
+      ~pk:companion_key_bls.alias
+      client
+  in
+  let* () = Client.bake_for_and_wait client in
+
+  Log.info "Waiting for companion key activation" ;
+  let* () = bake_n_cycles (consensus_rights_delay + 1) client in
+
+  Log.info "Checking key is activated" ;
+  let* () =
+    check_companion_key
+      ~__LOC__
+      delegate
+      ~expected_active:companion_key_bls
+      client
+  in
+  let* () =
+    check_validators_companion_key ~__LOC__ delegate ~expected:None client
+  in
+  let* current_level = get_current_level client in
+  let* () =
+    check_validators_companion_key
+      ~__LOC__
+      ~level:(current_level.level + 1)
+      delegate
+      ~expected:(Some companion_key_bls.public_key_hash)
+      client
+  in
   unit
 
 let register ~protocols =
-  let () = test_update_companion_key protocols in
-  ()
+  test_update_companion_key protocols ;
+  test_update_companion_key_without_consensus_key protocols
diff --git a/tezt/tests/expected/companion_key.ml/Alpha- update companion key without updating consensus key.out b/tezt/tests/expected/companion_key.ml/Alpha- update companion key without updating consensus key.out
new file mode 100644
index 0000000000000000000000000000000000000000..873da678c3bc0b7563a90436f6054bac8507c770
--- /dev/null
+++ b/tezt/tests/expected/companion_key.ml/Alpha- update companion key without updating consensus key.out	
@@ -0,0 +1,27 @@
+
+./octez-client --wait none set companion key for bootstrap1 to companion_key
+Node is bootstrapped.
+Estimated gas: 1744.502 units (will add 100 for safety)
+Estimated storage: no bytes added
+Operation successfully injected in the node.
+Operation hash is '[OPERATION_HASH]'
+NOT waiting for the operation to be included.
+Use command
+  octez-client wait for [OPERATION_HASH] to be included --confirmations 1 --branch [BLOCK_HASH]
+and/or an external block explorer to make sure that it has been included.
+This sequence of operations was run:
+  Manager signed operations:
+    From: [PUBLIC_KEY_HASH]
+    Fee to the baker: ꜩ0.000559
+    Expected counter: 1
+    Gas limit: 1845
+    Storage limit: 0 bytes
+    Balance updates:
+      [PUBLIC_KEY_HASH] ... -ꜩ0.000559
+      payload fees(the block proposer) ....... +ꜩ0.000559
+    Update_companion_key:
+      Public key hash: [PUBLIC_KEY_HASH]
+      Proof of possession: [BLS_SIGNATURE]
+      This companion key update was successfully applied
+      Consumed gas: 1744.436
+