title: Global System for Mobile Communication (GSM) categories: [cheatsheets]

tags: [mobile]

Global System for Mobile Communication (GSM)

Worldwide standard for mobile Communication.

Glossary:

AuC = Authentication Center
BSS = Base Station Sub-System
BSC = Base Station Controller
BTS = Base Transiever Station
IMSI = International Mobile Subscriber Identification
MSISDN = Mobile Subscriber International ISDN Number
SIM = Subscriber Identitiy Module

Architecture

Authentication works with a Challenge-Response Protocoll.

Authentication Vector: (Ri, SRES*i, Kbsc,msi)

Beeing:

Ri - from the AuC choosen random number
SRES*i = A3(Ri, Kms) (Signed Response)
Kms - Authentication key (saved in the SIM)
Kbsc,msi - Session Key after successfull authentication
Kbsc,msi = A8(Ri, Kms)

A3() and A8() are cryptographically secure hash functions

More about the authentication:

http://www.teletopix.org/gsm/how-authentication-center-auc-works-in-gsm/