From 9b11341ffdac7f364659b8906f7cd1e308ba6683 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=D0=A1=D0=B5=D1=80=D0=B3=D0=B5=D0=B9=20=D0=9F=D1=80=D0=BE?=
 =?UTF-8?q?=D1=85=D0=BE=D1=80=D0=BE=D0=B2?= <seriy.pr@gmail.com>
Date: Wed, 3 Oct 2018 22:04:15 +0200
Subject: [PATCH] Simplify obfuscated handshake parsing

---
 src/mtp_obfuscated.erl | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/src/mtp_obfuscated.erl b/src/mtp_obfuscated.erl
index 740af94..8a136be 100644
--- a/src/mtp_obfuscated.erl
+++ b/src/mtp_obfuscated.erl
@@ -66,17 +66,15 @@ from_header(Header, Secret) when byte_size(Header) == 64  ->
     {DecKey, DecIV} = init_up_decrypt(Header, Secret),
     St = new(EncKey, EncIV, DecKey, DecIV),
     {<<_:56/binary, Bin1:8/binary, _/binary>>, St1} = decrypt(Header, St),
-    <<HeaderPart:56/binary, _/binary>> = Header,
-    NewHeader = <<HeaderPart/binary, Bin1/binary>>,
-    case NewHeader of
-        <<_:56/binary, 16#ef, 16#ef, 16#ef, 16#ef, _/binary>> ->
-            DcId = get_dc(NewHeader),
+    case Bin1 of
+        <<16#ef, 16#ef, 16#ef, 16#ef, _/binary>> ->
+            DcId = get_dc(Bin1),
             {ok, DcId, mtp_abridged, St1};
-        <<_:56/binary, 16#ee, 16#ee, 16#ee, 16#ee, _/binary>> ->
-            DcId = get_dc(NewHeader),
+        <<16#ee, 16#ee, 16#ee, 16#ee, _/binary>> ->
+            DcId = get_dc(Bin1),
             {ok, DcId, mtp_intermediate, St1};
-        <<_:56/binary, 16#dd, 16#dd, 16#dd, 16#dd, _/binary>> ->
-            DcId = get_dc(NewHeader),
+        <<16#dd, 16#dd, 16#dd, 16#dd, _/binary>> ->
+            DcId = get_dc(Bin1),
             {ok, DcId, mtp_secure, St1};
         _ ->
             metric:count_inc([?APP, protocol_error, total], 1, #{labels => [unknown]}),
@@ -96,7 +94,7 @@ init_up_decrypt(Bin, Secret) ->
     KeyHash = crypto:hash('sha256', <<Key/binary, Secret/binary>>),
     {KeyHash, IV}.
 
-get_dc(<<_:60/binary, DcId:16/signed-little-integer, _/binary>>) ->
+get_dc(<<_:4/binary, DcId:16/signed-little-integer, _/binary>>) ->
     DcId.