diff --git a/src/lib_client_base_unix/client_signer_encrypted.ml b/src/lib_client_base_unix/client_signer_encrypted.ml
index 751f3381a..b81b4b260 100644
--- a/src/lib_client_base_unix/client_signer_encrypted.ml
+++ b/src/lib_client_base_unix/client_signer_encrypted.ml
@@ -114,7 +114,7 @@ module Encrypted_signer : SIGNER = struct
     let key = Crypto_box.Secretbox.of_bytes_exn (pbkdf ~password ~salt) in
     let msg = Data_encoding.Binary.to_bytes Signature.Secret_key.encoding sk in
     let encrypted_passwd = Crypto_box.Secretbox.box key msg nonce in
-    let payload = MBytes.(to_string (concat salt encrypted_passwd)) in
+    let payload = MBytes.(to_string (concat "" [salt; encrypted_passwd])) in
     let location = Base58.safe_encode payload in
     Hashtbl.replace decrypted_sks location sk ;
     return (Secret_key_locator.create ~scheme ~location)
diff --git a/src/lib_crypto/chain_id.ml b/src/lib_crypto/chain_id.ml
index 4c7cff6e4..648fc23f4 100644
--- a/src/lib_crypto/chain_id.ml
+++ b/src/lib_crypto/chain_id.ml
@@ -15,7 +15,7 @@ let name = "Chain_id"
 let title = "Network identifier"
 
 let extract bh =
-  MBytes.substring (Block_hash.to_bytes bh) 0 4
+  MBytes.sub_string (Block_hash.to_bytes bh) 0 4
 let hash_bytes ?key l = extract (Block_hash.hash_bytes ?key l)
 let hash_string ?key l = extract (Block_hash.hash_string ?key l)
 
diff --git a/src/lib_crypto/crypto_box.ml b/src/lib_crypto/crypto_box.ml
index d43686534..12fb6c41e 100644
--- a/src/lib_crypto/crypto_box.ml
+++ b/src/lib_crypto/crypto_box.ml
@@ -51,7 +51,7 @@ let random_keypair () =
   let pk, sk = Box.keypair () in
   sk, pk, hash pk
 
-let zero_nonce = Tweetnacl.Nonce.(of_bytes_exn (MBytes.init bytes '\x00'))
+let zero_nonce = Tweetnacl.Nonce.(of_bytes_exn (MBytes.make bytes '\x00'))
 let random_nonce = Nonce.gen
 let increment_nonce = Nonce.increment
 
diff --git a/src/lib_crypto/ed25519.ml b/src/lib_crypto/ed25519.ml
index d9f5a4d7c..f493973b7 100644
--- a/src/lib_crypto/ed25519.ml
+++ b/src/lib_crypto/ed25519.ml
@@ -258,7 +258,7 @@ include Helpers.MakeEncoder(struct
 
 let pp ppf t = Format.fprintf ppf "%s" (to_b58check t)
 
-let zero = MBytes.init size '\000'
+let zero = MBytes.make size '\000'
 
 let sign key msg = Sign.detached ~key msg
 
diff --git a/src/lib_crypto/secp256k1.ml b/src/lib_crypto/secp256k1.ml
index 8b74d3bed..a809a7d66 100644
--- a/src/lib_crypto/secp256k1.ml
+++ b/src/lib_crypto/secp256k1.ml
@@ -237,7 +237,7 @@ include Helpers.MakeEncoder(struct
 
 let pp ppf t = Format.fprintf ppf "%s" (to_b58check t)
 
-let zero = of_bytes_exn (MBytes.init size '\000')
+let zero = of_bytes_exn (MBytes.make size '\000')
 
 let sign sk msg =
   Sign.sign_exn context ~sk msg
diff --git a/src/lib_crypto/signature.ml b/src/lib_crypto/signature.ml
index 88ed72a6e..1fbf60c9d 100644
--- a/src/lib_crypto/signature.ml
+++ b/src/lib_crypto/signature.ml
@@ -462,10 +462,10 @@ let check public_key signature message =
   | Public_key.Secp256k1 _, Ed25519 _ -> false
 
 let append sk msg =
-  MBytes.concat msg (to_bytes (sign sk msg))
+  MBytes.concat "" [msg; (to_bytes (sign sk msg))]
 
 let concat msg signature =
-  MBytes.concat msg (to_bytes signature)
+  MBytes.concat "" [msg; (to_bytes signature)]
 
 type algo =
   | Ed25519
diff --git a/src/lib_data_encoding/binary.ml b/src/lib_data_encoding/binary.ml
index ff6bf47db..88fb1a22f 100644
--- a/src/lib_data_encoding/binary.ml
+++ b/src/lib_data_encoding/binary.ml
@@ -229,12 +229,12 @@ module Writer = struct
 
   let fixed_kind_string length s buf ofs =
     if String.length s <> length then invalid_arg "fixed_kind_string";
-    MBytes.blit_from_string s 0 buf ofs length;
+    MBytes.blit_of_string s 0 buf ofs length;
     ofs + length
 
   let variable_length_string s buf ofs =
     let length = String.length s in
-    MBytes.blit_from_string s 0 buf ofs length ;
+    MBytes.blit_of_string s 0 buf ofs length ;
     ofs + length
 
   let objs w1 w2 (v1,v2) buf ofs =
@@ -651,7 +651,7 @@ module Reader = struct
     ofs + length, s
 
   let fixed_length_string length buf ofs _len =
-    let s = MBytes.substring buf ofs length in
+    let s = MBytes.sub_string buf ofs length in
     ofs + length, s
 
   let seq r1 r2 buf ofs len =
diff --git a/src/lib_data_encoding/binary_stream.ml b/src/lib_data_encoding/binary_stream.ml
index 5a924415c..adefb1f26 100644
--- a/src/lib_data_encoding/binary_stream.ml
+++ b/src/lib_data_encoding/binary_stream.ml
@@ -139,7 +139,7 @@ let fixed_length_bytes length buf =
   generic_read_data length MBytes.sub buf
 
 let fixed_length_string length buf =
-  generic_read_data length MBytes.substring buf
+  generic_read_data length MBytes.sub_string buf
 
 let read_tag = function
   | `Uint8 -> uint8
diff --git a/src/lib_p2p/p2p_socket.ml b/src/lib_p2p/p2p_socket.ml
index 0452ca0d0..6d40f8fc6 100644
--- a/src/lib_p2p/p2p_socket.ml
+++ b/src/lib_p2p/p2p_socket.ml
@@ -35,7 +35,7 @@ module Crypto = struct
     let msglen = MBytes.length msg in
     fail_unless
       (msglen <= max_content_length) P2p_errors.Invalid_message_size >>=? fun () ->
-    let buf = MBytes.init (msglen + Crypto_box.zerobytes) '\x00' in
+    let buf = MBytes.make (msglen + Crypto_box.zerobytes) '\x00' in
     MBytes.blit msg 0 buf Crypto_box.zerobytes msglen ;
     let local_nonce = cryptobox_data.local_nonce in
     cryptobox_data.local_nonce <- Crypto_box.increment_nonce local_nonce ;
@@ -52,7 +52,7 @@ module Crypto = struct
     let header_buf = MBytes.create header_length in
     P2p_io_scheduler.read_full ~len:header_length fd header_buf >>=? fun () ->
     let encrypted_length = MBytes.get_uint16 header_buf 0 in
-    let buf = MBytes.init (encrypted_length + Crypto_box.boxzerobytes) '\x00' in
+    let buf = MBytes.make (encrypted_length + Crypto_box.boxzerobytes) '\x00' in
     P2p_io_scheduler.read_full
       ~pos:Crypto_box.boxzerobytes ~len:encrypted_length fd buf >>=? fun () ->
     let remote_nonce = cryptobox_data.remote_nonce in
diff --git a/src/lib_protocol_environment/sigs/v1/mBytes.mli b/src/lib_protocol_environment/sigs/v1/mBytes.mli
index 8c9cdec2c..f089d1b3a 100644
--- a/src/lib_protocol_environment/sigs/v1/mBytes.mli
+++ b/src/lib_protocol_environment/sigs/v1/mBytes.mli
@@ -20,14 +20,11 @@ val sub: t -> int -> int -> t
     and of length [len]. No copying of elements is involved: the
     sub-array and the original array share the same storage space. *)
 
-val shift: t -> int -> t
-(** [shift src ofs] is equivalent to [sub src ofs (length src - ofs)] *)
-
 val blit: t -> int -> t -> int -> int -> unit
 (** [blit src ofs_src dst ofs_dst len] copy [len] bytes from [src]
     starting at [ofs_src] into [dst] starting at [ofs_dst]. *)
 
-val blit_from_string: string -> int -> t -> int -> int -> unit
+val blit_of_string: string -> int -> t -> int -> int -> unit
 (** See [blit] *)
 
 val blit_to_bytes: t -> int -> bytes -> int -> int -> unit
@@ -39,8 +36,8 @@ val of_string: string -> t
 val to_string: t -> string
 (** [to_string b] dump the array content in a [string]. *)
 
-val substring: t -> int -> int -> string
-(** [substring b ofs len] is equivalent to [to_string (sub b ofs len)]. *)
+val sub_string: t -> int -> int -> string
+(** [sub_string b ofs len] is equivalent to [to_string (sub b ofs len)]. *)
 
 
 
@@ -129,7 +126,7 @@ val (>=) : t -> t -> bool
 val (>) : t -> t -> bool
 val compare : t -> t -> int
 
-val concat: t -> t -> t
+val concat: string -> t list -> t
 
 val to_hex: t -> [ `Hex of string ]
 val of_hex: [ `Hex of string ] -> t
diff --git a/src/lib_stdlib/jbuild b/src/lib_stdlib/jbuild
index 835fdc87a..818fa95c7 100644
--- a/src/lib_stdlib/jbuild
+++ b/src/lib_stdlib/jbuild
@@ -4,6 +4,8 @@
  ((name tezos_stdlib)
   (public_name tezos-stdlib)
   (libraries (ocplib-endian.bigstring
+              bigstring
+              cstruct
               hex
               re
               zarith
diff --git a/src/lib_stdlib/mBytes.ml b/src/lib_stdlib/mBytes.ml
index 05d27c897..24a0be90d 100644
--- a/src/lib_stdlib/mBytes.ml
+++ b/src/lib_stdlib/mBytes.ml
@@ -7,97 +7,23 @@
 (*                                                                        *)
 (**************************************************************************)
 
-open Bigarray
-
-type t = (char, int8_unsigned_elt, c_layout) Array1.t
-
-let create sz = Array1.create char c_layout sz
-let length = Array1.dim
-let sub = Array1.sub
-let shift ba off = sub ba off (length ba - off)
-let blit src srcoff dst dstoff len =
-  Array1.blit (sub src srcoff len) (sub dst dstoff len)
-let copy ba =
-  let ba' = create (Array1.dim ba) in
-  Array1.blit ba ba';
-  ba'
-let fill = Array1.fill
-
-let init sz v =
-  let b = create sz in
-  fill b v ;
-  b
-
-(** Adapted from ocaml-cstruct. *)
-
-external unsafe_blit_string_to_bigstring
-  : string -> int -> t -> int -> int -> unit
-  = "caml_blit_string_to_bigstring" [@@noalloc]
-
-external unsafe_blit_bigstring_to_bytes
-  : t -> int -> bytes -> int -> int -> unit
-  = "caml_blit_bigstring_to_string" [@@noalloc]
-
-(** HACK: force Cstruct at link which provides the previous primitives. *)
-let _dummy = Cstruct.byte_to_int
-
-let invalid_bounds j l =
-  Printf.sprintf "invalid bounds (index %d, length %d)" j l
-
-let blit_from_string src srcoff dst dstoff len =
-  if len < 0 || srcoff < 0 || dstoff < 0 || String.length src - srcoff < len then
-    raise (Invalid_argument (invalid_bounds srcoff len));
-  if length dst - dstoff < len then
-    raise (Invalid_argument (invalid_bounds dstoff len));
-  unsafe_blit_string_to_bigstring src srcoff dst dstoff len
-
-let blit_to_bytes src srcoff dst dstoff len =
-  if len < 0 || srcoff < 0 || dstoff < 0 || length src - srcoff < len then
-    raise (Invalid_argument (invalid_bounds srcoff len));
-  if Bytes.length dst - dstoff < len then
-    raise (Invalid_argument (invalid_bounds dstoff len));
-  unsafe_blit_bigstring_to_bytes src srcoff dst dstoff len
-
-let to_string buf =
-  let sz = length buf in
-  let s = Bytes.create sz in
-  unsafe_blit_bigstring_to_bytes buf 0 s 0 sz;
-  Bytes.unsafe_to_string s
-
-let of_string buf =
-  let buflen = String.length buf in
-  let c = create buflen in
-  unsafe_blit_string_to_bigstring buf 0 c 0 buflen;
-  c
-
-let to_hex s = Hex.of_cstruct (Cstruct.of_bigarray s)
-let of_hex s = Cstruct.to_bigarray (Hex.to_cstruct s)
-
-let substring src srcoff len =
-  if len < 0 || srcoff < 0 || length src - srcoff < len then
-    raise (Invalid_argument (invalid_bounds srcoff len));
-  let s = Bytes.create len in
-  unsafe_blit_bigstring_to_bytes src srcoff s 0 len;
-  Bytes.unsafe_to_string s
+include Bigstring
 
 include EndianBigstring.BigEndian
+module LE = EndianBigstring.LittleEndian
+
 include Compare.Make(struct
     type nonrec t = t
     let compare = Pervasives.compare
   end)
 
-module LE = struct
-  include EndianBigstring.LittleEndian
-end
+let make sz c =
+  let buf = create sz in
+  fill buf c ;
+  buf
 
-let concat b1 b2 =
-  let l1 = length b1 in
-  let l2 = length b2 in
-  let b = create (l1 + l2) in
-  blit b1 0 b 0 l1 ;
-  blit b2 0 b l1 l2 ;
-  b
+let to_hex t =
+  Hex.of_cstruct (Cstruct.of_bigarray t)
 
-let pp_hex ppf t =
-  let `Hex s = to_hex t in
-  Format.pp_print_string ppf s
+let of_hex hex =
+  Cstruct.to_bigarray (Hex.to_cstruct hex)
diff --git a/src/lib_stdlib/mBytes.mli b/src/lib_stdlib/mBytes.mli
index 883197d97..638c3e6c5 100644
--- a/src/lib_stdlib/mBytes.mli
+++ b/src/lib_stdlib/mBytes.mli
@@ -12,143 +12,12 @@
     Default layout for numeric operations is big-endian.
     Little-endian operations in the LE submodule. **)
 
-open Bigarray
-
-(** Arrays are of characters, represented as uint8's, in row-major layout. *)
-type t = (char, int8_unsigned_elt, c_layout) Array1.t
+include module type of Bigstring
 include Compare.S with type t := t
 
-val create: int -> t
-(** [create n] allocates and returns an array of size [n] **)
+include EndianBigstring.EndianBigstringSig
+module LE : EndianBigstring.EndianBigstringSig
 
-val init: int -> char -> t
-(** [init n c] allocates and returns an array of size [n] initialized
-    with [c]. *)
-
-val length: t -> int
-
-val copy: t -> t
-val fill: t -> char -> unit
-
-val sub: t -> int -> int -> t
-(** [sub src ofs len] extract a sub-array of [src] starting at [ofs]
-    and of length [len]. No copying of elements is involved: the
-    sub-array and the original array share the same storage space. *)
-
-val shift: t -> int -> t
-(** [shift src ofs] is equivalent to [sub src ofs (length src - ofs)] *)
-
-val blit: t -> int -> t -> int -> int -> unit
-(** [blit src ofs_src dst ofs_dst len] copy [len] bytes from [src]
-    starting at [ofs_src] into [dst] starting at [ofs_dst]. *)
-
-val blit_from_string: string -> int -> t -> int -> int -> unit
-(** See [blit] *)
-
-val blit_to_bytes: t -> int -> bytes -> int -> int -> unit
-(** See [blit] *)
-
-val of_string: string -> t
-(** [of_string s] create an byte array filled with the same content than [s]. *)
-
-val to_string: t -> string
-(** [to_string b] dump the array content in a [string]. *)
-
-val substring: t -> int -> int -> string
-(** [substring b ofs len] is equivalent to [to_string (sub b ofs len)]. *)
-
-(** Functions reading and writing bytes  *)
-
-val get_char: t -> int -> char
-(** [get_char buff i] reads 1 byte at offset i as a char *)
-
-val get_uint8: t -> int -> int
-(** [get_uint8 buff i] reads 1 byte at offset i as an unsigned int of 8
-    bits. i.e. It returns a value between 0 and 2^8-1 *)
-
-val get_int8: t -> int -> int
-(** [get_int8 buff i] reads 1 byte at offset i as a signed int of 8
-    bits. i.e. It returns a value between -2^7 and 2^7-1 *)
-
-val set_char: t -> int -> char -> unit
-(** [set_char buff i v] writes [v] to [buff] at offset [i] *)
-
-val set_int8: t -> int -> int -> unit
-(** [set_int8 buff i v] writes the least significant 8 bits of [v]
-    to [buff] at offset [i] *)
-
-(** Functions reading according to Big Endian byte order *)
-
-val get_uint16: t -> int -> int
-(** [get_uint16 buff i] reads 2 bytes at offset i as an unsigned int
-      of 16 bits. i.e. It returns a value between 0 and 2^16-1 *)
-
-val get_int16: t -> int -> int
-(** [get_int16 buff i] reads 2 byte at offset i as a signed int of
-      16 bits. i.e. It returns a value between -2^15 and 2^15-1 *)
-
-val get_int32: t -> int -> int32
-(** [get_int32 buff i] reads 4 bytes at offset i as an int32. *)
-
-val get_int64: t -> int -> int64
-(** [get_int64 buff i] reads 8 bytes at offset i as an int64. *)
-
-val get_float: t -> int -> float
-(** [get_float buff i] reads 4 bytes at offset i as an IEEE754 float. *)
-
-val get_double: t -> int -> float
-(** [get_float buff i] reads 8 bytes at offset i as an IEEE754 double. *)
-
-val set_int16: t -> int -> int -> unit
-(** [set_int16 buff i v] writes the least significant 16 bits of [v]
-    to [buff] at offset [i] *)
-
-val set_int32: t -> int -> int32 -> unit
-(** [set_int32 buff i v] writes [v] to [buff] at offset [i] *)
-
-val set_int64: t -> int -> int64 -> unit
-(** [set_int64 buff i v] writes [v] to [buff] at offset [i] *)
-
-val set_float: t -> int -> float -> unit
-(** [set_float buff i v] writes [v] to [buff] at offset [i] *)
-
-val set_double: t -> int -> float -> unit
-(** [set_double buff i v] writes [v] to [buff] at offset [i] *)
-
-module LE: sig
-
-  (** Functions reading according to Little Endian byte order *)
-
-  val get_uint16: t -> int -> int
-  (** [get_uint16 buff i] reads 2 bytes at offset i as an unsigned int
-      of 16 bits. i.e. It returns a value between 0 and 2^16-1 *)
-
-  val get_int16: t -> int -> int
-  (** [get_int16 buff i] reads 2 byte at offset i as a signed int of
-      16 bits. i.e. It returns a value between -2^15 and 2^15-1 *)
-
-  val get_int32: t -> int -> int32
-  (** [get_int32 buff i] reads 4 bytes at offset i as an int32. *)
-
-  val get_int64: t -> int -> int64
-  (** [get_int64 buff i] reads 8 bytes at offset i as an int64. *)
-
-  val set_int16: t -> int -> int -> unit
-  (** [set_int16 buff i v] writes the least significant 16 bits of [v]
-      to [buff] at offset [i] *)
-
-  val set_int32: t -> int -> int32 -> unit
-  (** [set_int32 buff i v] writes [v] to [buff] at offset [i] *)
-
-  val set_int64: t -> int -> int64 -> unit
-  (** [set_int64 buff i v] writes [v] to [buff] at offset [i] *)
-
-end
-
-val concat: t -> t -> t
-(** Returns a new array with adjacent copies of the two input arrays **)
-
-val to_hex: t -> Hex.t
-val of_hex: Hex.t -> t
-
-val pp_hex: Format.formatter -> t -> unit
+val make : int -> char -> t
+val of_hex : Hex.t -> t
+val to_hex : t -> Hex.t
diff --git a/src/lib_stdlib/mBytes_buffer.ml b/src/lib_stdlib/mBytes_buffer.ml
index 41cc1075f..9950740ed 100644
--- a/src/lib_stdlib/mBytes_buffer.ml
+++ b/src/lib_stdlib/mBytes_buffer.ml
@@ -71,7 +71,7 @@ let write_double buf float =
 let write_string_data buf str =
   let len = String.length str in
   resize_if_necessary buf len ;
-  MBytes.blit_from_string str 0 buf.buffer buf.offset len ;
+  MBytes.blit_of_string str 0 buf.buffer buf.offset len ;
   buf.offset <- buf.offset + len
 
 let write_sized buffer (writer : unit -> unit) =
diff --git a/src/proto_alpha/lib_protocol/src/unclaimed_public_key_hash.ml b/src/proto_alpha/lib_protocol/src/unclaimed_public_key_hash.ml
index fdf37a34b..67aeae370 100644
--- a/src/proto_alpha/lib_protocol/src/unclaimed_public_key_hash.ml
+++ b/src/proto_alpha/lib_protocol/src/unclaimed_public_key_hash.ml
@@ -19,7 +19,7 @@ let zero = MBytes.of_string (String.make size '\000')
 let to_b58check s =
   Ed25519.Public_key_hash.to_b58check
     (Ed25519.Public_key_hash.of_bytes_exn
-       (MBytes.concat s zero))
+       (MBytes.concat "" [s; zero]))
 
 let of_b58check_exn s =
   let pkh = Ed25519.Public_key_hash.of_b58check_exn s in