587 lines
20 KiB
TeX
587 lines
20 KiB
TeX
% $Header: /cvsroot/latex-beamer/latex-beamer/solutions/conference-talks/conference-ornate-20min.en.tex,v 1.7 2007/01/28 20:48:23 tantau Exp $
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\documentclass{beamer}
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% This file is a solution template for:
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% - Talk at a conference/colloquium.
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% - Talk length is about 20min.
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% - Style is ornate.
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% Copyright 2004 by Till Tantau <tantau@users.sourceforge.net>.
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%
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% In principle, this file can be redistributed and/or modified under
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% the terms of the GNU Public License, version 2.
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%
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% However, this file is supposed to be a template to be modified
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% for your own needs. For this reason, if you use this file as a
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% template and not specifically distribute it as part of a another
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% package/program, I grant the extra permission to freely copy and
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% modify this file as you see fit and even to delete this copyright
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% notice.
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\mode<presentation>
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{
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\usetheme{Warsaw}
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% or ...
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\setbeamercovered{transparent}
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% or whatever (possibly just delete it)
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}
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\usepackage[english]{babel}
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% or whatever
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\usepackage[latin1]{inputenc}
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% or whatever
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\usepackage{times}
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\usepackage[T1]{fontenc}
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% Or whatever. Note that the encoding and the font should match. If T1
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% does not look nice, try deleting the line with the fontenc.
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\title{GSM security nightmares}
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\subtitle
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{Running your own GSM network with OpenBSC}
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\author{Harald Welte}
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\institute
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{gnumonks.org\\gpl-violations.org\\OpenBSC\\airprobe.org\\hmw-consulting.de}
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% - Use the \inst command only if there are several affiliations.
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% - Keep it simple, no one is interested in your street address.
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\date[DORS/CLUC 2010] % (optional, should be abbreviation of conference name)
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{DORS/CLUC 2010, May 2010, Zagreb/Croatia}
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% - Either use conference name or its abbreviation.
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% - Not really informative to the audience, more for people (including
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% yourself) who are reading the slides online
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\subject{GSM Security}
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% This is only inserted into the PDF information catalog. Can be left
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% out.
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% If you have a file called "university-logo-filename.xxx", where xxx
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% is a graphic format that can be processed by latex or pdflatex,
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% resp., then you can add a logo as follows:
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% \pgfdeclareimage[height=0.5cm]{university-logo}{university-logo-filename}
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% \logo{\pgfuseimage{university-logo}}
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% Delete this, if you do not want the table of contents to pop up at
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% the beginning of each subsection:
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%\AtBeginSubsection[]
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%{
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% \begin{frame}<beamer>{Outline}
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% \tableofcontents[currentsection,currentsubsection]
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% \end{frame}
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%}
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% If you wish to uncover everything in a step-wise fashion, uncomment
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% the following command:
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%\beamerdefaultoverlayspecification{<+->}
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\begin{document}
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\begin{frame}
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\titlepage
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\end{frame}
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\begin{frame}{Outline}
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\tableofcontents
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% You might wish to add the option [pausesections]
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\end{frame}
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% Structuring a talk is a difficult task and the following structure
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% may not be suitable. Here are some rules that apply for this
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% solution:
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% - Exactly two or three sections (other than the summary).
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% - At *most* three subsections per section.
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% - Talk about 30s to 2min per frame. So there should be between about
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% 15 and 30 frames, all told.
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% - A conference audience is likely to know very little of what you
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% are going to talk about. So *simplify*!
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% - In a 20min talk, getting the main ideas across is hard
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% enough. Leave out details, even if it means being less precise than
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% you think necessary.
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% - If you omit details that are vital to the proof/implementation,
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% just say so once. Everybody will be happy with that.
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\begin{frame}{About the speaker}
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\begin{itemize}
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\item Using + playing with Linux since 1994
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\item Kernel / bootloader / driver / firmware development since 1999
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\item IT security specialist, focus on network protocol security
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\item Board-level Electrical Engineering
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\item Always looking for interesting protocols (RFID, DECT, GSM)
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\end{itemize}
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\end{frame}
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\section{GSM/3G security}
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\begin{frame}{GSM/3G protocol security}
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\begin{itemize}
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\item Observation
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\begin{itemize}
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\item Both GSM/3G and TCP/IP protocol specs are publicly available
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\item The Internet protocol stack (Ethernet/Wifi/TCP/IP) receives lots of scrutiny
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\item GSM networks are as widely deployed as the Internet
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\item Yet, GSM/3G protocols receive no such scrutiny!
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\end{itemize}
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\item There are reasons for that:
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\begin{itemize}
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\item GSM industry is extremely closed (and closed-minded)
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\item Only about 4 closed-source protocol stack implementations
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\item GSM chipset makers never release any hardware documentation
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\end{itemize}
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\end{itemize}
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\end{frame}
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\subsection{The closed GSM industry}
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\begin{frame}{The closed GSM industry}{Handset manufacturing side}
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\begin{itemize}
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\item Only very few companies build GSM/3.5G baseband chips today
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\begin{itemize}
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\item Those companies buy the operating system kernel and the protocol stack from third parties
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\end{itemize}
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\item Only very few handset makers are large enough to become a customer
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\begin{itemize}
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\item Even they only get limited access to hardware documentation
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\item Even they never really get access to the firmware source
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\end{itemize}
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\end{itemize}
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\end{frame}
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\begin{frame}{The closed GSM industry}{Network manufacturing side}
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\begin{itemize}
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\item Only very few companies build GSM network equipment
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\begin{itemize}
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\item Basically only Ericsson, Nokia-Siemens, Alcatel-Lucent and Huawei
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\item Exception: Small equipment manufacturers for picocell / nanocell / femtocells / measurement devices and law enforcement equipment
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\end{itemize}
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\item Only operators buy equipment from them
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\item Since the quantities are low, the prices are extremely high
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\begin{itemize}
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\item e.g. for a BTS, easily 10-40k EUR
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\end{itemize}
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\end{itemize}
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\end{frame}
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\begin{frame}{The closed GSM industry}{Operator side}
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\begin{itemize}
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\item Operators are mainly banks today
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\item Typical operator outsources
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\begin{itemize}
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\item Billing
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\item Network planning / deployment / servicing
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\end{itemize}
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\item Operator just knows the closed equipment as shipped by manufacturer
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\item Very few people at an operator have knowledge of the protocol beyond what's needed for operations and maintenance
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\end{itemize}
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\end{frame}
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\subsection{Security implications}
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\begin{frame}{The closed GSM industry}{Security implications}
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The security implications of the closed GSM industry are:
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\begin{itemize}
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\item Almost no people who have detailed technical knowledge outside the protocol stack or GSM network equipment manufacturers
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\item No independent research on protocol-level security
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\begin{itemize}
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\item If there's security research at all, then only theoretical (like the A5/2 and A5/1 cryptanalysis)
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\item Or on application level (e.g. mobile malware)
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\end{itemize}
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\item No open source protocol implementations
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\begin{itemize}
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\item which are key for making more people learn about the protocols
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\item which enable quick prototyping/testing by modifying existing code
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\end{itemize}
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\end{itemize}
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\end{frame}
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\begin{frame}{Security analysis of GSM}{How would you get started?}
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If you were to start with GSM protocol level security analysis, where and
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how would you start?
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\begin{itemize}
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\item On the handset side?
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\begin{itemize}
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\item Difficult since GSM firmware and protocol stacks are closed and proprietary
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\item Even if you want to write your own protocol stack, the layer 1 hardware and signal processing is closed and undocumented, too
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\item Known attempts
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\begin{itemize}
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\item The TSM30 project as part of the THC GSM project
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\item mados, an alternative OS for Nokia DTC3 phones
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\end{itemize}
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\item none of those projects successful so far
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\end{itemize}
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\end{itemize}
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\end{frame}
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\begin{frame}{Security analysis of GSM}{How would you get started?}
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If you were to start with GSM protocol level security analysis, where and
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how would you start?
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\begin{itemize}
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\item On the network side?
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\begin{itemize}
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\item Difficult since equipment is not easily available and normally extremely expensive
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\item However, network is very modular and has many standardized/documented interfaces
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\item Thus, if equipment is available, much easier/faster progress
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\end{itemize}
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\end{itemize}
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\end{frame}
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\begin{frame}{Security analysis of GSM}{The bootstrapping process}
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\begin{itemize}
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\item Read GSM specs day and night (> 1000 PDF documents) ;)
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\item Gradually grow knowledge about the protocols
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\item Obtain actual GSM network equipment (BTS)
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\item Try to get actual protocol traces as examples
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\item Start a complete protocol stack implementation from scratch
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\item Finally, go and play with GSM protocol security
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\end{itemize}
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\end{frame}
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\subsection{The GSM network}
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\begin{frame}{The GSM network}
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\begin{figure}[h]
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\centering
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\includegraphics[width=100mm]{gsm_network.png}
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\end{figure}
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\end{frame}
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\begin{frame}{GSM network components}
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\begin{itemize}
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\item The BSS (Base Station Subsystem)
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\begin{itemize}
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\item MS (Mobile Station): Your phone
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\item BTS (Base Transceiver Station): The {\em cell tower}
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\item BSC (Base Station Controller): Controlling up to hundreds of BTS
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\end{itemize}
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\item The NSS (Network Sub System)
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\begin{itemize}
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\item MSC (Mobile Switching Center): The central switch
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\item HLR (Home Location Register): Database of subscribers
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\item AUC (Authentication Center): Database of authentication keys
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\item VLR (Visitor Location Register): For roaming users
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\item EIR (Equipment Identity Register): To block stolen phones
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\end{itemize}
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\end{itemize}
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\end{frame}
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\begin{frame}{GSM network interfaces}
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\begin{itemize}
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\item Um: Interface between MS and BTS
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\begin{itemize}
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\item the only interface that is specified over radio
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\end{itemize}
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\item A-bis: Interface between BTS and BSC
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\item A: Interface between BSC and MSC
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\item B: Interface between MSC and other MSC
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\end{itemize}
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GSM networks are a prime example of an asymmetric distributed network,
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very different from the end-to-end transparent IP network.
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\end{frame}
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\subsection{The GSM protocols}
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\begin{frame}{GSM network protocols}{On the Um interface}
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\begin{itemize}
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\item Layer 1: Radio Layer, TS 04.04
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\item Layer 2: LAPDm, TS 04.06
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\item Layer 3: Radio Resource, Mobility Management, Call Control: TS 04.08
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\item Layer 4+: for USSD, SMS, LCS, ...
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\end{itemize}
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\end{frame}
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\begin{frame}{GSM network protocols}{On the A-bis interface}
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\begin{itemize}
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\item Layer 1: Typically E1 line, TS 08.54
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\item Layer 2: A variant of ISDN LAPD with fixed TEI's, TS 08.56
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\item Layer 3: OML (Organization and Maintenance Layer, TS 12.21)
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\item Layer 3: RSL (Radio Signalling Link, TS 08.58)
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\item Layer 4+: transparent messages that are sent to the MS via Um
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\end{itemize}
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\end{frame}
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\section{Implementing GSM protocols}
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\subsection{Getting started}
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\begin{frame}{Implementing GSM protocols}{How I got started!}
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\begin{itemize}
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\item In September 2008, we were first able to make the BTS active and see it on a phone
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\begin{itemize}
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\item This is GSM900 BTS with 2 TRX at 2W output power (each)
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\item A 48kg monster with attached antenna
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\item 200W power consumption, passive cooling
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\item E1 physical interface
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\end{itemize}
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\item I didn't have much time at the time (day job at Openmoko)
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\item Started to read up on GSM specs whenever I could
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\item Bought a HFC-E1 based PCI E1 controller, has mISDN kernel support
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\item Found somebody in the GSM industry who provided protocol traces
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\end{itemize}
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\end{frame}
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\subsection{Timeline}
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\begin{frame}{Implementing GSM protocols}{Timeline}
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\begin{itemize}
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\item In November 2008, I started the development of OpenBSC
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\item In December 2008, we did a first demo at 25C3
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\item In January 2009, we had full voice call support
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\item In June 2009, I started with actual security related stuff
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\item In August 2009, we had the first field test with 2BTS and > 860 phones
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\end{itemize}
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\end{frame}
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\subsection{OpenBSC}
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\begin{frame}{Security analysis of GSM}{OpenBSC}
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What is OpenBSC
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\begin{itemize}
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\item A {\em GSM network in a box} software
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\item Implements minimal subset of BSC, MSC, HLR, SMSC
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\item Is Free and Open Source Software licensed under GNU GPL
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\item Supports Siemens BS-11 BTS (E1) and ip.access nanoBTS (IP based)
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\item Has classic 2G signalling, voice and SMS support
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\item Implements various GSM protocols like
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\begin{itemize}
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\item A-bis RSL (TS 08.58) and OML (TS 12.21)
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\item TS 04.08 Radio Resource, Mobility Management, Call Control
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\item TS 04.11 Short Message Service
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\end{itemize}
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\end{itemize}
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\end{frame}
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\section{Security analysis}
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\subsection{Theory}
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\begin{frame}{Known GSM security problems}{Scientific papers, etc}
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\begin{itemize}
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\item No mutual authentication between phone and network
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\begin{itemize}
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\item leads to rogue network attacks
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\item leads to man-in-the-middle attacks
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\item is what enables IMSI-catchers
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\end{itemize}
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\item Weak encryption algorithms
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\item Encryption is optional, user does never know when it's active or not
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\item DoS of the RACH by means of channel request flooding
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\item RRLP (Radio Resource Location Protocol)
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\begin{itemize}
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\item the network can obtain GPS fix or even raw GSM data from the phone
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\item combine that with the network not needing to authenticate itself
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\end{itemize}
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\end{itemize}
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\end{frame}
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\subsection{The Baseband}
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\begin{frame}{Known GSM security problems}{The Baseband side}
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\begin{itemize}
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\item GSM protocol stack always runs in a so-called baseband processor (BP)
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\item What is the baseband processor
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\begin{itemize}
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\item Typically ARM7 (2G/2.5G phones) or ARM9 (3G/3.5G phones)
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\begin{itemize}
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\item Runs some RTOS (often Nucleus, sometimes L4)
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\item No memory protection between tasks
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\end{itemize}
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\item Some kind of DSP, model depends on vendor
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\begin{itemize}
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\item Runs the digital signal processing for the RF Layer 1
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\item Has hardware peripherals for A5 encryption
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\end{itemize}
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\end{itemize}
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\item The software stack on the baseband processor
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\begin{itemize}
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\item is written in C and assembly
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\item lacks any modern security features (stack protection, non-executable pages, address space randomization, ..)
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\end{itemize}
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\end{itemize}
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\end{frame}
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\subsection{Observations}
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\begin{frame}{Interesting observations}{Learned from implementing the stack}
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While developing OpenBSC, we observed a number of interesting
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\begin{itemize}
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\item Many phones use their TMSI from the old network when they roam to a new network
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\item Various phones crash when confronted with incorrect messages. We didn't even start to intentionally send incorrect messages (!)
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\item There are tons of obscure options on the GSM spec which no real network uses. Potential attack vector by using rarely tested code paths.
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\end{itemize}
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\end{frame}
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\subsection{GSM Protocol Fuzzing}
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\begin{frame}{GSM Protocol Fuzzing}{Theoretical basis}
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How to do GSM protocol fuzzing
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\begin{itemize}
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\item From the handset to the network
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\begin{itemize}
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\item Basically impossible due to closeness of baseband
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\item However, some incomplete projects working on it
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\end{itemize}
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\item From the network side
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\begin{itemize}
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\item Easy in case of {\em rogue network} attacks
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\item Fuzzing target is the GSM stack in the baseband processor
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\end{itemize}
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\item As an A-bis man in the middle
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\begin{itemize}
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\item Needs access to an A-bis interface of an actual network
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\item Very attractive, since no encryption and ability to fuzz both network and handset
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\end{itemize}
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\end{itemize}
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\end{frame}
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\begin{frame}{A-bis injection}{for A-bis over IP}
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How to do inject messages into A-bis over IP?
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\begin{itemize}
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\item Problem
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\begin{itemize}
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\item A-bis/IP uses one TCP connection for OML and RSL messages
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\item OML initialization is essential for BTS to become operational
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\item TCP makes insertion of additional messages relatively hard
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\end{itemize}
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\item Solution: Build an {\em A-bis injection proxy}
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\begin{itemize}
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\item Transparently pass OML and RSL packets between BTS and BSC
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\item Add additional stateless UDP sockets for injecting messages, one socket each for
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\end{itemize}
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\begin{itemize}
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\item injecting OML/RSL to the network
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\item injecting OML/RSL to the BTS
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\end{itemize}
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\end{itemize}
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\end{frame}
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\begin{frame}{A-bis Injection Proxy}{Principle of operation}
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\begin{itemize}
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\item Proxy needs to be brought between BTS and BSC
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\item Luckily, A-bis/IP SSL support not always used
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\item Thus, physical access to the Ethernet link sufficient
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\item Configure system with two interfaces
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\begin{itemize}
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\item BSC-facing interface has IP of BTS
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\item BTS-facing interface has IP of BSC / default gw
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\end{itemize}
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\item BTS will make TCP connection to proxy
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\item proxy will make independent TCP connection to BSC
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\end{itemize}
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\end{frame}
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\begin{frame}{scapy GSM support}{The actual fuzzing}
|
|
How to actually craft the packets for the fuzzing
|
|
\begin{itemize}
|
|
\item GSM has many, many protocols
|
|
\item Writing custom code will be a hard-coded special case for each of them
|
|
\item Solution: Use scapy and implement the GSM protocols as scapy "layers"
|
|
\begin{itemize}
|
|
\item IPA protocol header
|
|
\item RSL protocol layer
|
|
\item RLL data indication / data request
|
|
\item GSM 04.08 RR / MM / CC messages
|
|
\end{itemize}
|
|
\end{itemize}
|
|
\end{frame}
|
|
|
|
\begin{frame}{OpenBSC silent calls}{A more elegant fuzzing interface}
|
|
\begin{itemize}
|
|
\item Injection at the A-bis level has many problems
|
|
\begin{itemize}
|
|
\item you can only do it while a call is active
|
|
\item you simply piggy-back on existing RR connections
|
|
\end{itemize}
|
|
\item The OpenBSC {\em silent call} feature can help
|
|
\begin{itemize}
|
|
\item we use OpenBSC to establish a RR connection
|
|
\item in the GSM master/slave model, the phone will not close a connection unless told to do so
|
|
\item we then send arbitrary data to the phone and receive its responses
|
|
\item this currently only works from within OpenBSC, but we'll provide UDP injection sockets soon
|
|
\end{itemize}
|
|
\end{itemize}
|
|
\end{frame}
|
|
|
|
\section{Summary}
|
|
|
|
\subsection{What we've learned}
|
|
|
|
\begin{frame}{Summary}{What we've learned}
|
|
\begin{itemize}
|
|
\item The GSM industry is making security analysis very difficult
|
|
\item It is well-known that the security level of the GSM stacks is very low
|
|
\item We now have multiple solutions for sending arbitrary protocol data
|
|
\begin{itemize}
|
|
\item From a rogue network to phones (OpenBSC, OpenBTS)
|
|
\item From an a-bis proxy to the network or the phones
|
|
\end{itemize}
|
|
\item There is ongoing work for a phone-based tool to fuzz the network
|
|
\end{itemize}
|
|
\end{frame}
|
|
|
|
\subsection{Where we go from here}
|
|
|
|
\begin{frame}{TODO}{Where we go from here}
|
|
\begin{itemize}
|
|
\item The tools for fuzzing mobile phone protocol stacks are available
|
|
\item It is up to the security community to make use of those tools (!)
|
|
\item Don't you too think that TCP/IP security is boring
|
|
\item Join the GSM protocol security research projects
|
|
\item Boldly go where no man has gone before
|
|
\end{itemize}
|
|
\end{frame}
|
|
|
|
\subsection{Where we go from here}
|
|
|
|
\begin{frame}{Current Areas of Work / Future plans}
|
|
\begin{itemize}
|
|
\item Packet data (GPRS/EDGE) support in OpenBSC
|
|
\begin{itemize}
|
|
\item GPRS/EDGE is used extensively on modern smartphones
|
|
\item Enables us to play on IP level with those phones without a heavily filtered operator network
|
|
\end{itemize}
|
|
\item UMTS(3G) support in OpenBSC
|
|
\item Access to MS side layer 1
|
|
\item Playing with SIM Toolkit from the operator side
|
|
\item Playing with MMS
|
|
\item More exploration of RRLP
|
|
\end{itemize}
|
|
\end{frame}
|
|
|
|
\subsection{Further Reading}
|
|
|
|
\begin{frame}{Further Reading}
|
|
\begin{itemize}
|
|
\item http://openbsc.gnumonks.org/
|
|
\item http://airprobe.org/
|
|
\item http://openbts.sourceforge.net/
|
|
\item http://bb.osmocom.org/
|
|
\end{itemize}
|
|
\end{frame}
|
|
|
|
\end{document}
|