In UMTS, security mechanism is developed to take care of all the gsm security shortfalls. UMTS security is also referred as 3G security.
Five security groups exist in 3G networks as shown in the figure.
• Network Access Security
• Network domain security
• User domain security
• Application domain security
• visibility, configurability of security
Network Access Security helps protect air interface and also provide 3g subscribers to access the 3g network securely. In UMTS authentication, key 'K' is shared between network and UE. The network transmits random generated number 'RAND' and 'AUTN' in the message authentication challenge to the UE. AUTN makes it possible for UE to authenticate the 3g network. USIM generates response back to the network with ciphering and integrity keys. This helps network authenticate the UE.
The major difference between gsm security and 3g security is that network authentication was not possible with gsm compliant UE. This is possible in UMTS compliant UE.
cipher key (Kc) in 3g security is of length 128 bits which was 64 bits in gsm. In gsm, ciphering was provided to air interface only and ciphering between MS and BTS is not provided. In UMTS, security is provided between UTRAN and RNC. Hence 3g security is extended between UE and RNC.
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