US Robotics USR2450 Informations techniques Page 20

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V 2.2 Copyright SystemExperts 2001,2002,2003
39
GSM Security
n International Mobile Equipment Identity (IMEI) for
each device to determine if device is allowed on the
network
n Shared secret: Stored in the Authentication Center
(AuC) and subscriber's SIM card
n Authentication: The AuC generates a random number sends it to
the mobile. Mobile uses A3 cipher and shared key to generate a
signed response sent back to the AuC
n Encryption: Use a key derived from A8 cipher using the same
pseudo random number+subscriber-key as above. Cipher key is
used with the TDMA frame number, in the A5 cipher to create a
value to XOR with data
n same process in IS-54/136 & PCS1900
V 2.2 Copyright SystemExperts 2001,2002,2003
40
Today’s Data Systems
n Primary mobile wireless data services are…
n Cellular Digital Packet Data (CDPD)
n iDEN packet service
n Circuit-switched data service for CDMA networks
(e.g., SprintPCS)
n Circuit-switched data services for GSM networks
n Modems and analog phones
n All of these services offer speeds in the 9.6 Kbps to
19.2 Kbps range
n How they deliver…
n Smart phones (phones with micro-browsers)
n Wireless modems (PC card or cable with phone)
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