GSM System Security

Security in the GSM system By Jeremy Quirke | Last updated 1 st May 2004 © 2004 AusMobile http://www.ausmobile.com SECURITY IN THE GSM SYSTEM ........................... .............. ................................................................ 1 INTRODUCTION ............................ .............. ............................ .............. .............. .............. ........................ 2 SECURITY FEATURES OFFERED BY GSM............................................ .............. ............................... 2 AUTHENTICATION ...................................................................................................................................... 3 The SIM card ...................................................................... .............. .............. .............. .............. .......... 3 Additional local security in the SIM...................................................................................................... 4 The A3 algorithm and authentication procedure ............................... .......... ........... ..................... ......... 4 Authentication failure ........................................................................................................................... 6 More on the A3 algorithm..................................................................................................................... 6 CIPHERING.................................................................................................................................................. 6 Ciphe ring algorithms............................................................ .............. .............. .............. ...................... 8 A NONYMITY............................................................................................................................................... 8 DISTRIBUTION OF THE AUTHENTICATION AND CIPHERING INFORMATION THROUGHOUT THE NETWORK ... 10 IMPLEMENTATIONS OF A3, A8 ................................................................................................................. 11 FREQUENCY HOPPING ............................................................................................................................... 11 FLAWS WITH THESE MEASURES ............ .............. ............................ .............. ............................ ...... 13 NETWORK DOES NOT AUTHENTICATE ITSELF TO A PHONE ........................................................................ 13 COMMON IMPLEMENTATION OF A3/A8 IS FLAWED – CONTAINS A NARROW PIPE ...................................... 13 COMMON IMPLEMENTATION OF A3/A8 IS FLAWED – REDUCES STRENGTH OF CIPHERING KEY K C............ 14 VULNERABILITIES IN THE SUBSCRIBER IDENTITY CONFIDENTIALITY MECHANISM .................................... 14 OVER THE AIR CRACKING OF K I................................................................................................................ 15 CIPHERING OCCURS AFTER FEC ............................................................................................................... 17 FLAWS IN A5/1 AND A5/2 ALGORITHM..................................................................................................... 18 MEASURES TAKEN TO ADDRESS THESE FLAWS .............. .............. ............................ ............. .... 18 GSM - NEWER A3/A8 IMPLEMENTATION................................................................................................. 18 GSM - A5/3 CIPHERING............................................................................................................................ 19 GPRS – GEA3 CIPHERING........................................................................................................................ 19 GPRS/UMTS – CIPHERING BEFORE FEC........................ ......................................................................... 19 UMTS – NETWORK AUTHENTICATION TO PHONE ..................................................................................... 19 UMTS – IMPROVED, STRONGER ALGORITHMS ......................................................................................... 20 Authentication and key generation...................................................................................................... 20 Ciphering and integrity....................................................................................................................... 21 CONCLUSION............................ .............. ............................ .............. ............................ .............. ............. 22 REFERENCES ............................ .............. ............................ .............. ............................ .............. ............. 23 APPENDIX A – A5/1 IMPLEMENTATION........ .............. .............. ............................ .............. ............. 24 BASIC ALGORITHM ................................................................................................................................... 24 I NITIAL STATE .......................................................................................................................................... 25 GENERATING CIPHER STREAM .................................................................................................................. 25 APPENDI X B – ALGORITHMS USED BY AUSTRALIAN OPERATORS...................... ................. 25 GSM/GPRS ............................................................................................................................................. 25

GSM System Security

Documents

Transcript of GSM System Security