use mirage-crypto Z_extra

src/crypto.ml

@@ -1,9 +1,6 @@
 open Syntax
 
 module Binary_format_rsa = struct
-  (* TODO tests:
-         - need to strip leading zeros?
-         - endianess ok? *)
   (* RSA public key binary format
        https://www.gnupg.org/documentation/manuals/gcrypt/MPI-formats.html
        := { uint16_be: n size; uint16_be: e size; n; e}
@@ -12,19 +9,9 @@ module Binary_format_rsa = struct
        leading zeroes are stripped unless they are required to keep a value positive
        no 0-termination *)
 
-  let rev_string len s = String.init len (fun i -> s.[len - 1 - i])
-
-  (* we reverse bytes because Z.of_bits reads bytes in little endian *)
-  let z_of_bits_be src pos len =
-    String.sub src pos len |> rev_string len |> Z.of_bits
-
-  let z_to_bits_be z =
-    let bits = Z.to_bits z in
-    rev_string (String.length bits) bits
-
   let z_array_to_octets (arr : Z.t array) =
     let nb = Array.length arr in
-    let bits_arr = Array.map z_to_bits_be arr in
+    let bits_arr = Array.map Mirage_crypto_pk.Z_extra.to_octets_be arr in
     let len_arr = Array.map String.length bits_arr in
     let len = (2 * nb) + Array.fold_left ( + ) 0 len_arr in
     let b = Bytes.make len '\x00' in
@@ -42,13 +29,10 @@ module Binary_format_rsa = struct
       bits_arr;
     Bytes.unsafe_to_string b
 
-  let check = function
-    | false -> Error "rsa of_octets error, invalid data"
-    | true -> Ok ()
-
   let z_array_of_octets ~nb s =
     let s_len = String.length s in
-    let* () = check (s_len > 2 * nb) in
+    if s_len <= 2 * nb then Error "rsa of_octets error"
+    else
       let pos = ref 0 in
       let len_arr =
         Array.init nb (fun _i ->
@@ -56,14 +40,14 @@ module Binary_format_rsa = struct
             pos := !pos + 2;
             len)
       in
-    let* () =
       let len = (2 * nb) + Array.fold_left ( + ) 0 len_arr in
-      check (s_len = len)
-    in
+      if s_len <> len then Error "rsa of_octets error"
+      else
         let z_arr =
           Array.init nb (fun i ->
               let len = len_arr.(i) in
-          let z = z_of_bits_be s !pos len in
+              let s = String.sub s !pos len in
+              let z = Mirage_crypto_pk.Z_extra.of_octets_be s in
               pos := !pos + len;
               z)
         in