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Securing Against Fraud in Mobile Communications: Systems Design and Development in 3G Mobile Networks By Securing Against Fraud in Mobile Communications: Systems Design and Development in 3G Mobile Networks by Yujiro Mochizuki M.S., Management of Technology,Massachusetts Institute of Technology, 2004 B.A., Economics, Keio University, 1996 Submitted to the Engineering Systems Division in Partial Fulfillment of the Requirements for the Degree of Master of Science in Technology and Policy at the Massachusetts Institute of Technology February 2006 © 2006, Yujiro Mochizuki. All rights reserved. The author hereby grants to MIT permission to reproduce and to distribute publicly paper and electronic copies of this thesis document in whole or in part. Signature of Author: ,c6ofgy and Policy Program, Eeering Systems Division November 12, 2005 Certified by: Michael Cusumano Slo/ Management Review Professor Management S0ach'fS/ of Management //1//./// / Thesis Supervisor Certified by: d-'b v (Y /Joel( Cutcher-Gershenfeld / xecutive Director, Engineering Systems Learning Center Senior Research Scientist, Sloan School of Management j/A_} fwA Thesis Reader / Accepted by: /Professor ad Dava J. Newman Professor of Aeronautics and A onautcs and Engineering Systems Director, Technology and Policy Program e_ . e OF TECHNOLOGY ARCH8VES MAY 3 12006 LIBRARIES Securing Against Fraud in Mobile Communications: Systems Design and Development in 3G Mobile Networks by Yujiro Mochizuki Submitted to the Engineering Systems Division on November 12, 2005 in Partial Fulfillment of the Requirements for the Degree of Master of Science in Technology and Policy ABSTRACT Network security ensures the consistency, integrity, and reliability of telecommunications systems. Authorized network access prevents fraudulent communications and maintains the availability of the systems. However, limited development time, cost reduction pressure and requirement for high reliability in software development have forced mobile carriers to implement the insufficient and inflexible authentication mechanisms. Technical specifications including network architecture, network protocols, and security algorithm are widely available to the public. In addition, both secured and unsecured networks are interconnected by global roaming services. The inadequate system design will make the mobile systems vulnerable to unauthorized access to mobile communications. Compared with GSM mobile systems, 3G mobile systems are equipped with more robust and flexible security mechanisms. The official position taken by mobile carriers, such as NTT DoCoMo, KDDI, and Vodafone, is that fraudulent communications, usually in the form of cloned mobile phones, are impossible with their 3G mobile systems. Examining the NTT DoCoMo's case, however, we find that this statement is based on weak security assumptions. In order to avoid potential threats and to secure the 3G mobile systems, this thesis (1) explores the security architecture and mechanisms in 3G systems, (2) analyzes the current platform architecture and platform innovations of the network software, and (3) suggests a secure system design and development. Thesis Supervisor: Michael A. Cusumano Title: Sloan Management Review Professor of Management 2 Table of Contents 1 Introduction ...................................................... 11 1.1 Operation of the 3G Systems ................................ 13 1.2 Purpose of This Thesis.................................. 15 1.3 Scope of This Thesis .................................. 17 1.4 Overview of the Core Network ...................................... 18 1.5 Thesis Structure ........................................ 22 2 Network Security in 3G Mobile Systems ...................................................... 23 2.1 Security Principles ...................................................... 23 2.2 3G Security Features ...................................................... 24 2.3 Security Architecture ...................................................... 25 2.4 Network Access Security Mechanisms ...................................................... 28 2.4.1 Authentication Procedure ...................................................... 28 2.4.2 Verification of Sequence Number (SQN) against Replay Attacks ..........................33 2.4.3 Generation of Authentication Vectors ...................................................... 35 2.5 Security Issues about 3G Mobile Networks ...................................................... 38 3 Network Software Development ...................................................... 40 3.1 Requirements for Network Software ..................................................... 40 3.1.1 Reliability (Maturity and Availability)...................................................... 42 3.1.2 Security ......................................................................................................... 43 3.1.3 Compatibility (Interoperability) ...................................................... 44 3.1.4 Real-time Response (Time Behavior) ...................................................... 46 3.1.5 Configurability for Geographical Distribution of the System (Maintainability) ....47 3.2 Platform Innovations in Network Software ...................................................... 48 3 3.2.1 Component Standardization ................................................... 50 3.2.2 Architectural Innovation and Product Architecture ................................................. 51 3.2.3 Product Platform and Product Family ................................................... 54 3.3 Difficulties in Platform Innovation ................................................... 56 3.3.1 Time-to-Market Pressure ................................................... 57 3.3.2 Pressures for Cost Reduction ................................................... 58 3.3.3 Requirements for High Reliability ................................................... 59 3.3.4 Complex Architecture . .................................................. 60 3.3.5 Scalability ................................................... 61 4 Analysis of the Existing Network Software ................................................... 63 4.1 Insufficient Implementation of the Authentication Mechanisms................................. 64 4.1.1 Insufficient SQN Management ................................................... 67 4.1.2 Support Only Fixed-length Parameters................................................... 70 4.1.3 No Support for AMF ................................................... 71 4.2 Reasons for Insufficient implementation ................................................... 72 4.2.1 Strategic Viewpoint .................................................. 75 4.2.2 Economic Viewpoint ................................................... 76 4.2.3 Engineering Viewpoint ................................................... 78 4.2.4 Political Viewpoint ................................................... 81 4.2.5 Social/Cultural Viewpoint ................................................... 82 4.3 Tradeoffs between Performance and Security ................................................... 83 4.3.1 Dynamic Steps ................................................... 83 4.3.2 Network Traffic ................................................... 86 4.3.3 CPU Usage.................................................................................................. 89 5 Securing Against Fraud in Mobile Communications ................................................... 92 4 5.1 Learning from DoCoMo's Network Software Development ...................................... 92 5.2 Strategies for Securing Mobile Systems ................................................. 94 5.2.1 Before Deployment ................................................. 96 5.2.2 After Deployment ................................................. 101 6 C onclusion.......................................................................................................... 107 6.1 Security in 3G Mobile Systems ................................................. 107 6.2 Lessons Learned in Actual 3G Mobile Systems ................................................. 108 6.3 Strategies for Mobile Carriers ................................................. 109 Abbreviations and Terminologies ......................................... 113 End Notes ......................................... 115 Bibliography......................................... 120 5 List of Figures Figure 1-1: Number of UMTS Networks Worldwide (Total as of January 2005) ............. 12 Figure 1-2: Market Share of Japanese Mobile Subscribers (Total as of October 2005) ...... 14 Figure 1-3: Market Share of Japanese 3G Mobile Subscribers (Total as of October 2005)14 Figure 1-4: Core Network in 3G (UMTS) Systems ............................................................ 20 Figure 1-5: Thesis Structure ............................................................. 22 Figure 2-1: UMTS Domains ............................................................. 26 Figure 2-2: Overview of the UMTS Security Architecture .................................................. 27 Figure 2-3: Authentication Mechanisms (Key Agreement) .................................................32 Figure 2-4: Verification of the SQN ............................................................. 34 Figure 2-5: Generation of the Authentication Vectors (AuC) .............................................. 35 Figure 2-6: User Authentication Function (USIM) ............. ............................... 36 Figure 3-1: Quality Model for External and Internal
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