diff --git a/src/git_kv.ml b/src/git_kv.ml
index 044a379..3a713bc 100644
--- a/src/git_kv.ml
+++ b/src/git_kv.ml
@@ -119,6 +119,12 @@ module SHA1 = struct
   include Digestif.SHA1
 
   let hash x = Hashtbl.hash x
+  let feed ctx ?off ?len ba = feed_bigstring ctx ?off ?len ba
+  let null = digest_string ""
+  let length = digest_size
+  let compare a b =
+    String.compare
+      (to_raw_string a) (to_raw_string b)
 end
 
 module Verbose = struct
@@ -128,7 +134,46 @@ module Verbose = struct
   let print _ = Lwt.return_unit
 end
 
+module Lwt_scheduler = struct
+  module Mutex = struct
+    type 'a fiber = 'a Lwt.t
+    type t = Lwt_mutex.t
+
+    let create () = Lwt_mutex.create ()
+    let lock t = Lwt_mutex.lock t
+    let unlock t = Lwt_mutex.unlock t
+  end
+
+  module Condition = struct
+    type 'a fiber = 'a Lwt.t
+    type mutex = Mutex.t
+    type t = unit Lwt_condition.t
+
+    let create () = Lwt_condition.create ()
+    let wait t mutex = Lwt_condition.wait ~mutex t
+    let signal t = Lwt_condition.signal t ()
+    let broadcast t = Lwt_condition.broadcast t ()
+  end
+
+  type 'a t = 'a Lwt.t
+
+  let bind x f = Lwt.bind x f
+  let return x = Lwt.return x
+  let parallel_map ~f lst = Lwt_list.map_p f lst
+  let parallel_iter ~f lst = Lwt_list.iter_p f lst
+  let detach f =
+    let th, wk = Lwt.wait () in
+    Lwt.async (fun () ->
+      let res = f () in
+      Lwt.wakeup_later wk res ;
+      Lwt.return_unit) ;
+   th
+end
+
+module Scheduler = Carton.Make (Lwt)
 module Delta = Carton_lwt.Enc.Delta (SHA1) (Verbose)
+module First_pass = Carton.Dec.Fp (SHA1)
+module Verify = Carton.Dec.Verify (SHA1) (Scheduler) (Lwt_scheduler)
 
 let pack t ~commit stream =
   let open Lwt.Infix in
@@ -201,29 +246,160 @@ let pack t ~commit stream =
   stream None ;
   Lwt.return_unit
 
-let to_octets t =
-  (* TODO maybe preserve edn and branch as well? *)
+let to_octets t = match t.head with
+  | None -> assert false (* TODO(dinosaure): empty PACK file *)
+  | Some commit ->
+    let buf = Buffer.create 0x100 in
+    let stream = Option.iter (Buffer.add_string buf) in
+    let open Lwt.Infix in
+    pack t.store ~commit stream >|= fun () ->
+    Buffer.contents buf
+
+let digest ~kind ?(off = 0) ?len buf =
+  let len =
+    match len with Some len -> len | None -> Bigstringaf.length buf - off in
+  let ctx = SHA1.empty in
+  let ctx =
+    match kind with
+    | `A -> SHA1.feed_string ctx (Fmt.str "commit %d\000" len)
+    | `B -> SHA1.feed_string ctx (Fmt.str "tree %d\000" len)
+    | `C -> SHA1.feed_string ctx (Fmt.str "blob %d\000" len)
+    | `D -> SHA1.feed_string ctx (Fmt.str "tag %d\000" len) in
+  let ctx = SHA1.feed_bigstring ctx ~off ~len buf in
+  SHA1.get ctx
+
+let analyze stream =
+  let where = Hashtbl.create 0x100 in
+  let child = Hashtbl.create 0x100 in
+  let sizes = Hashtbl.create 0x100 in
+
+  let replace tbl k v = match Hashtbl.find_opt tbl k with
+    | Some v' -> if v' < v then Hashtbl.replace tbl k v
+    | _ -> Hashtbl.add tbl k v in
+
+  let rec go acc tmp decoder = let open Lwt.Infix in
+    match First_pass.decode decoder with
+    | `Await decoder ->
+      ( stream () >>= function
+      | Some str ->
+        let tmp = Bigstringaf.of_string str ~off:0 ~len:(String.length str) in
+        go acc tmp (First_pass.src decoder tmp 0 (String.length str))
+      | None -> failwith "Truncated PACK file" )
+    | `Peek decoder ->
+      let keep = First_pass.src_rem decoder in
+      ( stream () >>= function
+      | Some str ->
+        let tmp = Bigstringaf.create (keep + String.length str) in
+        Bigstringaf.blit tmp ~src_off:0 tmp ~dst_off:0 ~len:keep ;
+        Bigstringaf.blit_from_string str ~src_off:0 tmp ~dst_off:keep 
+          ~len:(String.length str) ;
+        go acc tmp (First_pass.src decoder tmp 0 (keep + String.length str))
+      | None -> failwith "Truncated PACK file" )
+    | `Entry ({ First_pass.kind= Base _; offset; size; _ }, decoder) ->
+      Hashtbl.add where offset (First_pass.count decoder - 1) ;
+      Hashtbl.add sizes offset size ;
+      go (Verify.unresolved_base ~cursor:offset :: acc) tmp decoder
+    | `Entry ({ First_pass.kind= Ofs { sub= v; source; target; }
+              ; offset; _ }, decoder) ->
+      Hashtbl.add where offset (First_pass.count decoder - 1) ;
+      replace sizes Int64.(sub offset (of_int v)) source ;
+      replace sizes offset target ;
+      ( try let vs = Hashtbl.find child (`Ofs Int64.(sub offset (of_int v))) in
+            Hashtbl.replace child (`Ofs Int64.(sub offset (of_int v))) (offset :: vs)
+        with _ -> Hashtbl.add child (`Ofs Int64.(sub offset (of_int v))) [ offset ] ) ;
+      go (Verify.unresolved_node :: acc) tmp decoder
+    | `Entry ({ First_pass.kind= Ref { ptr; target; source; }
+              ; offset; _ }, decoder) ->
+      Hashtbl.add where offset (First_pass.count decoder - 1) ;
+      replace sizes offset (Stdlib.max target source) ;
+      ( try let vs = Hashtbl.find child (`Ref ptr) in
+            Hashtbl.replace child (`Ref ptr) (offset :: vs)
+        with _ -> Hashtbl.add child (`Ref ptr) [ offset ] ) ;
+      go (Verify.unresolved_node :: acc) tmp decoder
+    | `End _hash ->
+      let where ~cursor = Hashtbl.find where cursor in
+      let children ~cursor ~uid =
+        match Hashtbl.find_opt child (`Ofs cursor),
+              Hashtbl.find_opt child (`Ref uid) with
+        | Some a, Some b -> List.sort_uniq compare (a @ b)
+        | Some x, None | None, Some x -> x
+        | None, None -> [] in
+      let weight ~cursor = Hashtbl.find sizes cursor in
+      let oracle = { Carton.Dec.where
+                   ; Carton.Dec.children
+                   ; Carton.Dec.digest
+                   ; Carton.Dec.weight } in
+      Lwt.return (List.rev acc, oracle)
+    | `Malformed err -> failwith err in
+
+  let o = Bigstringaf.create De.io_buffer_size in
+  let allocate _ = De.make_window ~bits:15 in
+  let decoder = First_pass.decoder ~o ~allocate `Manual in
   let open Lwt.Infix in
-  match t.head with
-  | None -> Lwt.return ""
-  | Some head ->
-    Store.read_exn t.store head >|= function
-    | Commit c ->
-      let l = Encore.to_lavoisier Git_commit.format in
-      Encore.Lavoisier.emit_string c l
-    | _ -> assert false
+  go [] De.bigstring_empty decoder >>= fun (matrix, oracle) ->
+  Lwt.return (Array.of_list matrix, oracle)
+
+let stream_of_string str =
+  let closed = ref false in
+  fun () -> match !closed with
+  | true -> Lwt.return_none
+  | false -> closed := true ; Lwt.return_some str
+
+let map contents ~pos len =
+  Bigstringaf.of_string ~off:(Int64.to_int pos) ~len contents
+
+let unpack contents =
+  let open Lwt.Infix in
+  analyze (stream_of_string contents) >>= fun (matrix, oracle) ->
+  let z = De.bigstring_create De.io_buffer_size in
+  let allocate bits = De.make_window ~bits in
+  let never _ = assert false in
+  let pack = Carton.Dec.make contents ~allocate ~z ~uid_ln:SHA1.length
+    ~uid_rw:SHA1.of_raw_string never in
+  Verify.verify ~threads:4 pack ~map ~oracle ~verbose:ignore ~matrix >>= fun () ->
+  let index = Hashtbl.create (Array.length matrix) in
+  let iter v =
+    let offset = Verify.offset_of_status v in
+    let hash = Verify.uid_of_status v in
+    Hashtbl.add index hash offset in
+  Array.iter iter matrix ;
+  let pack =
+    Carton.Dec.make contents ~allocate ~z ~uid_ln:SHA1.length
+      ~uid_rw:SHA1.of_raw_string (Hashtbl.find index) in
+  init_store ()
+  >|= Rresult.R.reword_error (Rresult.R.msgf "%a" Store.pp_error)
+  >|= Rresult.R.failwith_error_msg >>= fun store ->
+  let rec go commit idx =
+    if idx < Array.length matrix
+    then
+      let cursor = Verify.offset_of_status matrix.(idx) in
+      let weight = Carton.Dec.weight_of_offset ~map pack ~weight:Carton.Dec.null cursor in
+      let raw = Carton.Dec.make_raw ~weight in
+      let v = Carton.Dec.of_offset ~map pack raw ~cursor in
+      let kind = match Carton.Dec.kind v with
+        | `A -> `Commit
+        | `B -> `Tree
+        | `C -> `Blob
+        | `D -> `Tag in
+      Store.write_inflated store ~kind
+        (Cstruct.of_bigarray ~off:0 ~len:(Carton.Dec.len v) (Carton.Dec.raw v)) >>= fun hash ->
+      ( if kind = `Commit
+        then Store.shallow store hash
+        else Lwt.return_unit ) >>= fun () ->
+      go (if kind = `Commit then Some hash else None) (succ idx)
+    else Lwt.return commit in
+  go None 0 >>= fun head -> Lwt.return (store, head)
 
 let of_octets ctx ~remote data =
   (* TODO maybe recover edn and branch from data as well? *)
-  let open Lwt_result.Infix in
-  let l = Encore.to_angstrom Git_commit.format in
-  Lwt.return
-    (Result.map_error (fun e -> `Msg e)
-       (Angstrom.parse_string ~consume:All l data)) >>= fun head ->
-  let head = Git_commit.tree head in
-  init_store () >|= fun store ->
-  let edn, branch = split_url remote in
-  { ctx ; edn ; branch ; store ; head = Some head }
+  let open Lwt.Infix in
+  Lwt.catch
+    (fun () ->
+       unpack data >>= fun (store, head) ->
+       let edn, branch = split_url remote in
+       Lwt.return_ok { ctx ; edn ; branch ; store ; head; })
+    (fun _exn ->
+       Lwt.return_error (`Msg "Invalid PACK file"))
 
 let exists t key =
   let open Lwt.Infix in
diff --git a/src/pack.ml b/src/pack.ml
new file mode 100644
index 0000000..8b13789
--- /dev/null
+++ b/src/pack.ml
@@ -0,0 +1 @@
+