GSM signal security

by

Ravikumar V

MSISDN = CC + NDC + SN

• MSISDN = Mobile Subscriber international

ISDN No.• CC = Country Code• NDC = National Destination Code• SN = Subscriber No.

MSRN = CC + NDC + SN

• MSRN = Mobile Station Roaming No.• SN in MSISDN->points a database in HLR• SN in MSRN ->points a database in VLR

IMSI = MCC + MNC + MSIN

• IMSI = International Mobile Subscriber Identity • MCC = Mobile Country Code• MNC = Mobile Network Code• MSIN = Mobile Subscriber Identification No.

Fixed line subscriber calling to mobile,mobile terminated call

LAI = MCC + MNC + LAC

• LAI = Location Area Identity• LAC = Location Area code

VLRLAC LAI

BSS

CGI = MCC + MNC + LAC +CI

• CI = Cell Identity• CGI = Cell Global Identity

BSSCI CGI

BTS MS

• Location Registration(1st time) getting through IMSI

• After every location regi. & newe location update,New TMSI is generated.

• LAI & TMSI saved in SIM• BTS’s LAI Compares SIM’s LAI every time

mobile receives data through control channels.• Generic location update->when MS enters in

new LA of other MSC/VLR.• Periodic location update->timer control

periodic updates.

• HON = Handover No.• HON is only used When inter MSC handover

occurs

HON = CC + NDC + SN

Authentication & ciphering

Authentication & ciphering

A3 & A8=Authentication A5=ciphering

RAND=Random no.SRES=Signed ResponseKi=authentication keyKc=ciphering key

NetworkAuthentication Request ( RAND + CKSN )Authentication Response ( SRES )A3/A8

Ki

FNo( Kc + CKSN )

( CKSN )

NetworkChannel Request

Immediate Assignment

( stored in SIM )

( stored in MSC/VLR )

Initial Message ( CKSN )

If CKSN Checked , No authentication

Ciphering Key Sequence No ( CKSN )MM - Common Procedures