diff --git a/src/lib_base/chain_id.ml b/src/lib_base/chain_id.ml
index a902e5861..eae5d23ac 100644
--- a/src/lib_base/chain_id.ml
+++ b/src/lib_base/chain_id.ml
@@ -16,8 +16,8 @@ module Raw = struct
 
   let extract bh =
     MBytes.substring (Block_hash.to_bytes bh) 0 4
-  let hash_bytes l = extract (Block_hash.hash_bytes l)
-  let hash_string l = extract (Block_hash.hash_string l)
+  let hash_bytes ?key l = extract (Block_hash.hash_bytes ?key l)
+  let hash_string ?key l = extract (Block_hash.hash_string ?key l)
 
   let size = 4
 
diff --git a/src/lib_crypto/blake2B.ml b/src/lib_crypto/blake2B.ml
index 19eebf91b..a44cdb2b3 100644
--- a/src/lib_crypto/blake2B.ml
+++ b/src/lib_crypto/blake2B.ml
@@ -73,13 +73,15 @@ module Make_minimal (K : Name) = struct
   let read src off = of_bytes_exn @@ MBytes.sub src off size
   let write dst off h = MBytes.blit (to_bytes h) 0 dst off size
 
-  let hash_bytes l =
-    let state = Blake2b.init size in
+  let hash_bytes ?key l =
+    let key = Option.map ~f:Cstruct.of_bigarray key in
+    let state = Blake2b.init ?key size in
     List.iter (fun b -> Blake2b.update state (Cstruct.of_bigarray b)) l ;
     Blake2b.final state
 
-  let hash_string l =
-    let state = Blake2b.init size in
+  let hash_string ?key l =
+    let key = Option.map ~f:Cstruct.of_string key in
+    let state = Blake2b.init ?key size in
     List.iter (fun s -> Blake2b.update state (Cstruct.of_string s)) l ;
     Blake2b.final state
 
diff --git a/src/lib_crypto/s.ml b/src/lib_crypto/s.ml
index 04ed704f3..1d143b82e 100644
--- a/src/lib_crypto/s.ml
+++ b/src/lib_crypto/s.ml
@@ -23,8 +23,8 @@ module type MINIMAL_HASH = sig
   val name: string
   val title: string
 
-  val hash_bytes: Cstruct.buffer list -> t
-  val hash_string: string list -> t
+  val hash_bytes: ?key:Cstruct.buffer -> Cstruct.buffer list -> t
+  val hash_string: ?key:string -> string list -> t
   val size: int (* in bytes *)
   val compare: t -> t -> int
   val equal: t -> t -> bool
diff --git a/src/lib_protocol_environment/sigs/v1/s.mli b/src/lib_protocol_environment/sigs/v1/s.mli
index 38e6c4505..edc048b43 100644
--- a/src/lib_protocol_environment/sigs/v1/s.mli
+++ b/src/lib_protocol_environment/sigs/v1/s.mli
@@ -49,8 +49,8 @@ module type MINIMAL_HASH = sig
   val name: string
   val title: string
 
-  val hash_bytes: MBytes.t list -> t
-  val hash_string: string list -> t
+  val hash_bytes: ?key:MBytes.t -> MBytes.t list -> t
+  val hash_string: ?key:string -> string list -> t
   val size: int (* in bytes *)
   val compare: t -> t -> int
   val equal: t -> t -> bool