From d5abae41b654aa95299e7d8796e85fd12863ce11 Mon Sep 17 00:00:00 2001
From: swrup <swrup@protonmail.com>
Date: Sat, 18 Oct 2025 15:28:04 +0200
Subject: [PATCH] encode/decode rsapublickey

---
 src/binary_formats.ml | 114 ++++++++++++++++++------------------------
 src/types.ml          |  12 ++---
 2 files changed, 53 insertions(+), 73 deletions(-)

diff --git a/src/binary_formats.ml b/src/binary_formats.ml
index 83cb48c9..4edb28a7 100644
--- a/src/binary_formats.ml
+++ b/src/binary_formats.ml
@@ -38,9 +38,56 @@
      ? only for "HashCode" and "ShortHashCode"
  *)
 
+module Taler_signatures = Include.Taler_signatures
+
 let int32_size = 4
 let int64_size = 8
 
+module RsaPublicKey = struct
+  (* https://www.gnupg.org/documentation/manuals/gcrypt/MPI-formats.html
+     format: { uint16_be: n size; uint16_be: e size; n; e}
+
+    integer in big-endian format (MSB first)
+    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])
+
+  (* todo: need to strip leading zeros or something? *)
+  (* 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 to_octets ({ n; e } : Mirage_crypto_pk.Rsa.pub) =
+    let n_len = Z.size n in
+    let e_len = Z.size e in
+    let len = 4 + n_len + e_len in
+    let b = Bytes.make len '\x00' in
+    Bytes.set_uint16_be b 0 n_len;
+    Bytes.set_uint16_be b 2 e_len;
+    let n = Z.to_bits n |> rev_string n_len in
+    let e = Z.to_bits e |> rev_string e_len in
+    Bytes.blit_string n 0 b 4 n_len;
+    Bytes.blit_string e 0 b (4 + n_len) e_len;
+    Bytes.unsafe_to_string b
+
+  let of_octets =
+    let check = function
+      | false -> Error "RsaPublicKey.of_octets: invalid data"
+      | true -> Ok ()
+    in
+    fun s ->
+      let open Syntax in
+      let len = String.length s in
+      let* () = check (len >= 4) in
+      let n_len = String.get_uint16_be s 0 in
+      let e_len = String.get_uint16_be s 2 in
+      let* () = check (len = n_len + e_len + 4) in
+      let n = z_of_bits_be s 4 n_len in
+      let e = z_of_bits_be s (4 + n_len) e_len in
+      Mirage_crypto_pk.Rsa.pub ~n ~e |> unwrap_err_msg
+end
+
 (* -- Time -- *)
 
 (* microseconds since the UNIX Epoch
@@ -238,77 +285,14 @@ module UTIL = struct
 end
 
 include UTIL
-module Taler_signatures = Include.Taler_signatures
 
 (* -- Cryptographic primitives -- *)
 
-(* GNUNET_CRYPTO format *)
-module GNUNET_RsaPublicKey = struct
-  (* libgnuutil format:
-     https://docs.gnunet.org/doxygen/d9/dbe/structGNUNET__CRYPTO__RsaPublicKeyHeaderP.html
-     https://docs.gnunet.org/doxygen/d6/d70/group__libgnunetutil.html#ga9c99a81e8cd649c1c925d23211a0738f
-     https://www.gnupg.org/documentation/manuals/gcrypt/MPI-formats.html
-
-    format:
-     - rsa header
-     - modulus
-     - public_exponent
-
-    integer in big-endian format (MSB first).
-    Leading zeroes are stripped unless they are required to keep a value positive.
-  *)
-  type header = {
-    n_len: int;
-    e_len: int;
-  }
-
-  type t = {
-    header: header;
-    n: Z.t;
-    e: Z.t;
-  }
-
-  (* todo: need to strip leading zeros or something? *)
-  (* Z.to_bits is in little endian but we need it in big endian *)
-  let z_to_bigendian_bits v =
-    let s = Z.to_bits v in
-    let len = String.length s in
-    let s = String.init len (fun i -> s.[len - 1 - i]) in
-    s
-
-  let header_bin =
-    let open Bin in
-    record (fun n_len e_len -> { n_len; e_len })
-    |+ field beint16 (fun t -> t.n_len)
-    |+ field beint16 (fun t -> t.e_len)
-    |> sealr
-
-  (* note: this one has a dynamic sizeof *)
-  let bin =
-    let open Bin in
-    record (fun header n e ->
-        let n = Z.of_bits n in
-        let e = Z.of_bits e in
-        { header; n; e })
-    |+ field header_bin (fun t -> t.header)
-    (* TODO
-       here it should not be [cstring] but [bytes t.header.n_len]
-       -> just parse this without Bin *)
-    |+ field cstring (fun t -> z_to_bigendian_bits t.n)
-    |+ field cstring (fun t -> z_to_bigendian_bits t.e)
-    |> sealr
-
-  let of_pub ({ n; e } : Mirage_crypto_pk.Rsa.pub) =
-    let header = { n_len= Z.size n; e_len= Z.size e } in
-    let t = { header; n; e } in
-    t
-end
-
 module DenominationHash = MK_SRC_HASH_32 (struct
   type src = Mirage_crypto_pk.Rsa.pub
 
-  let to_octets pub =
-    GNUNET_RsaPublicKey.of_pub pub |> Bin.to_string GNUNET_RsaPublicKey.bin
+  (* function to convert src type to a string for hashing *)
+  let to_octets = RsaPublicKey.to_octets
 end)
 
 module ExchangePublicKeyP = struct
diff --git a/src/types.ml b/src/types.ml
index 45e9b7a2..0df429f6 100644
--- a/src/types.ml
+++ b/src/types.ml
@@ -132,19 +132,15 @@ end = struct
 end
 
 module RsaPublicKey = struct
-  type t = Mirage_crypto_pk.Rsa.pub
+  open Binary_formats.RsaPublicKey
 
-  let to_octets ({ n; e } : Mirage_crypto_pk.Rsa.pub) =
-    let open Binary_formats.GNUNET_RsaPublicKey in
-    let header = { n_len= Z.size n; e_len= Z.size e } in
-    let v = { header; n; e } in
-    let s = Bin.to_string bin v in
-    s
+  type t = Mirage_crypto_pk.Rsa.pub
 
   let of_b32 s =
     let open Syntax in
+    let open Binary_formats.RsaPublicKey in
     let* s = B32.decode s in
-    let* v = Util.bin_of_string Binary_formats.GNUNET_RsaPublicKey.bin s in
+    let* v = of_octets s in
     let+ v = Mirage_crypto_pk.Rsa.pub ~n:v.n ~e:v.e |> unwrap_err_msg in
     v