LINE-Source

Project of Reverse Engineering LINE Messaging App (for education purpose)

INFO

This project was carried out in order to obtain and make the thrift file of LINE Thrift Protocol (client-side).

And also, feel free to contribute 😄

Prerequisites

Before doing this, you need to have this on you:

• Java 1.8 or greater (Get it here)
• Thrift types understanding on a compiled thrift (Read this)
• Some apk decompiler (I'm using jadx)
• A little good understanding of java

How to

This is how i obtain the thrift file and make it human-readable form:

• Download LINE App from playstore using downloader like Evozi
  • If you're downloading a new version of LINE (maybe version 8 or greater), you'll get zip file instead of apk file. Don't worry, just extract the file and you'll find the apk (jp.naver.line.android.apk)
• Decompile apk using your decompiler (you have to decompile it into a java file)
• Now search for the new TStruct("thisIsStruct") code in a *.java file
  • But that's not an easy thing to do, the new TStruct("thisIsStruct") is definitely obfuscated by the developer and it can be something like this new A340v("thisIsStruct"). You have to figure it out by yourself
• And the result must be like this (if you're using jadx)
  • 
  • The blabla_args is a request struct, and the blabla_result is a response struct
  • In a request you could get field thrift data
  • In a response you could get responsetype and throws/exception data
• Now just click one of the result with _args in it, and you'll be redirected to the package source
  • 
  • verifyEapLogin is the struct name
  • new C6282b(arg1,arg2,arg3) is a struct field builder, but you see that it have 3 arguments. So here is the explanation :
    • OAuthWebLoginServiceActivity.f1422071 is a field name (should be string), but we got something like that. Because of the name is not a string, you have to explore the OAuthWebLoginServiceActivity.f1422071 to get the name.
    • (byte) 12 is a type of a field. (12 = struct)
    • 1 is the id of a field.
• After that, you have to scroll down a little bit and you'll get like this
  • 
  • As you can see, it's similar to the struct builder before. But this one is more useful for gathering more information.
  • So, if you found a field with struct,enum,map<byte,byte>,set<byte>,list<byte> type. You should gather information on static {.....} scope (like image above).
• And now you can make it into human-readable form, the result must be like this
  • RESPONSETYPE_STRUCT verifyEapLogin(1: OAUTHACTIVITY_STRUCT field_name) throws(1: EXCEPTION_STRUCT e)
• So, that's how to obtain and build LINE Thrift Protocol (client-side)