diff --git a/vendors/ocaml-bip39/bip39.opam b/vendors/ocaml-bip39/bip39.opam
index 9c7501a4c..e772d957c 100644
--- a/vendors/ocaml-bip39/bip39.opam
+++ b/vendors/ocaml-bip39/bip39.opam
@@ -15,7 +15,8 @@ depends: [
   "dune" {build & = "1.0.1"}
   "base" {build & >= "v0.10.0"}
   "stdio" {build & >= "v0.10.0"}
-  "nocrypto" {>= "0.5.4"}
+  "hacl"
+  "bigstring" {>= "0.2"}
   "pbkdf" {>= "0.2.0"}
   "hex" {test & >= "1.2.0"}
   "alcotest" {test & >= "0.8.1"}
diff --git a/vendors/ocaml-bip39/src/bip39.ml b/vendors/ocaml-bip39/src/bip39.ml
index 03fbe0dd1..45232ec0e 100644
--- a/vendors/ocaml-bip39/src/bip39.ml
+++ b/vendors/ocaml-bip39/src/bip39.ml
@@ -8,14 +8,14 @@ open StdLabels
 let acceptable_num_words = [12 ; 15 ; 18 ; 21 ; 24]
 
 type entropy = {
-  bytes : Cstruct.t ;
+  bytes : Bigstring.t ;
   length : int ;
   digest_length : int ;
   num_words : int ;
 }
 
 let entropy_of_bytes bytes =
-  match Cstruct.len bytes with
+  match Bigstring.length bytes with
   | 16 -> Some { bytes ; length = 16 ; digest_length = 4 ; num_words = 12 }
   | 20 -> Some { bytes ; length = 20 ; digest_length = 5 ; num_words = 15 }
   | 24 -> Some { bytes ; length = 24 ; digest_length = 6 ; num_words = 18 }
@@ -112,16 +112,16 @@ let of_entropy entropy =
   match entropy_of_bytes entropy with
   | None -> invalid_arg "Bip39.of_entropy: wrong entropy length"
   | Some { bytes ; digest_length ; _ } ->
-      let digest = Cstruct.get_char (Nocrypto.Hash.SHA256.digest entropy) 0 in
+      let digest = Bigstring.get (Hacl.Hash.SHA256.digest entropy) 0 in
       let digest = list_sub (bits_of_char digest) digest_length in
-      let entropy = bits_of_bytes (Cstruct.to_string bytes) @ digest in
+      let entropy = bits_of_bytes (Bigstring.to_string bytes) @ digest in
       List.map (pack entropy 11) ~f:int_of_bits
 
-let to_seed ?(passphrase="") t =
+let to_seed ?(passphrase=Bigstring.empty) t =
   let words = to_words t in
-  let password = Cstruct.of_string (String.concat ~sep:" " words) in
-  let salt = Cstruct.of_string ("mnemonic" ^ passphrase) in
-  Pbkdf.pbkdf2 ~prf:`SHA512 ~password ~salt ~count:2048 ~dk_len:64l
+  let password = Bigstring.of_string (String.concat ~sep:" " words) in
+  let salt = Bigstring.(concat "" [of_string "mnemonic" ; passphrase]) in
+  Pbkdf.SHA512.pbkdf2 ~password ~salt ~count:2048 ~dk_len:64l
 
 (*---------------------------------------------------------------------------
    Copyright (c) 2017 Vincent Bernardoff
diff --git a/vendors/ocaml-bip39/src/bip39.mli b/vendors/ocaml-bip39/src/bip39.mli
index fc2b4bd56..87f7236b5 100644
--- a/vendors/ocaml-bip39/src/bip39.mli
+++ b/vendors/ocaml-bip39/src/bip39.mli
@@ -28,13 +28,13 @@ val to_words : t -> string list
 (** [to_words mnemonic] is the list of words corresponding to
     [mnemonic]. *)
 
-val of_entropy : Cstruct.t -> t
+val of_entropy : Bigstring.t -> t
 (** [of_entropy bytes] is the mnemonic derived from [bytes].
 
     @raises [Invalid_argument] is [List.length bytes] is not in { 16,
     20, 24, 28, 32 }. *)
 
-val to_seed : ?passphrase:string -> t -> Cstruct.t
+val to_seed : ?passphrase:Bigstring.t -> t -> Bigstring.t
 (** [to_seed ?passphrase mnemonic] is 64 bytes derived from a BIP39
     mnemonic [mnemonic], using the optional passphrase [passphrase] if
     provided. *)
diff --git a/vendors/ocaml-bip39/src/dune b/vendors/ocaml-bip39/src/dune
index 06b0d9d82..06bda597c 100644
--- a/vendors/ocaml-bip39/src/dune
+++ b/vendors/ocaml-bip39/src/dune
@@ -2,7 +2,7 @@
  (name        bip39)
  (public_name bip39)
  (modules english bip39)
- (libraries nocrypto pbkdf))
+ (libraries bigstring hacl pbkdf))
 
 (rule
  (targets english.ml)
diff --git a/vendors/ocaml-bip39/test/test.ml b/vendors/ocaml-bip39/test/test.ml
index 0fbef0880..efb30cbb7 100644
--- a/vendors/ocaml-bip39/test/test.ml
+++ b/vendors/ocaml-bip39/test/test.ml
@@ -121,11 +121,12 @@ let pp_diff ppf (l1, l2) =
 let vectors () =
   ListLabels.iteri vectors ~f:begin fun i { entropy ; words ; seed } ->
     let words = String.split_on_char ' ' words in
-    let mnemonic = Bip39.of_entropy (Cstruct.of_string (Hex.to_string entropy)) in
+    let mnemonic = Bip39.of_entropy (Cstruct.to_bigarray (Hex.to_cstruct entropy)) in
     let words_computed = Bip39.to_words mnemonic in
     assert (words = words_computed) ;
-    let seed_computed = Bip39.to_seed ~passphrase:"TREZOR" mnemonic in
-    assert ((Hex.to_cstruct seed) = seed_computed)
+    let seed_computed =
+      Bip39.to_seed ~passphrase:(Bigstring.of_string "TREZOR") mnemonic in
+    assert (Cstruct.to_bigarray (Hex.to_cstruct seed) = seed_computed)
   end
 
 let basic = [