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Implications of Unlicensed Mobile Access for GSM security. From : Proceeding of the First International Conference on Security and Privacy for Emerging Areas in Communications Networks, 2005 Author : Sandro Grech, Pasi Eronen Presented by : Ying Long Chen. Outline.

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implications of unlicensed mobile access for gsm security

Implications of Unlicensed Mobile Access for GSM security

From:Proceeding of the First International

Conference on Security and Privacy for Emerging

Areas in Communications Networks, 2005

Author:Sandro Grech, Pasi Eronen

Presented by:Ying Long Chen

outline
Outline
  • Overview of UMA
    • Introduction
    • Background: GSM and GPRS security
    • UMA overview
  • Security Analysis
  • Protecting against the attack
  • Conclusion
introduction
Introduction
  • Why UMA
    • Indoor coverage issue for GSM
    • Bandwidth issue
    • The standardization work is continued by 3GPP
gsm and gprs security
GSM and GPRS Security
  • Authentication:avoid fraudulent access by a cloned MS
  • Encryption:avoid unauthorized listening
  • Parameters:
    • Ki:used to achieve authentication(128 bit)
      • Ki is stored in AUC and SIM
      • Ki is not known to the subscriber
    • Rand:128-bit random number by the home system
    • SRES:32-bit generated by Algorithm A3
    • Kc:generated by Algorithm A8 for the encryption
    • Frame number:a TDMA frame number encoded in the data bits
gsm and gprs security1
GSM and GPRS Security
  • Authentication algorithm:
    • A3
      • Authentication function
      • Stored in AUC and SIM
  • Encryption algorithm:
    • A8
      • To generated the encryption key
      • Stored in AUC and SIM
    • A5
      • An algorithm stored in the MS (handset hardware) and the visit system
      • Used for data ciphering and deciphering
uma overview
UMA overview

UMA security mechanisms

uma overview1
UMA overview

1. Unlicensed Interface Security:

  • Outside the scope of UMA

2. Up Interface Security

  • Traffic between the phone and the UNC is protected by IPSec ESP tunnel, which is established and maintained using IKEv2

3. CN authentication, GPRS ciphering

  • The authentication between the phone and UNC does not replace the normal GSM authentication between the phone and MSC

4. Data application security

  • Outside the scope of UMA
uma security mechanisms
UMA Security Mechanisms
  • Authentication Mechanisms
    • UMA stage 2 states that mutual authentication between Mobile Station and UNC shall be accomplished using Internet Key Exchange (IKEv2) protocol and the Extensible Authentication Protocol (EAP)
  • Confidentiality Mechanisms
    • IPsec protect all signal and user traffic sent between MS and UNC-SGW over the Up interface.
uma security mechanisms1
UMA Security Mechanisms
  • Integrity Mechanisms
    • As part of IPsec, messages could be integrity protected. IPsec use a hash with a secret key to provide integrity protection. This scheme is called an HMAC(Hashed Message Authentication Code)
  • User Credentials
    • All long-term security credentials used for subscriber and network authentication are stored on the SIM
uma security analysis
UMA Security Analysis
  • IKEv2
    • IMSI not protected enough
      • During the initial stage of the EAP-SIM and EAP-AKA procedures, when the Mobile Station sends IKE SA INIT, it will transfer its Network Access Identifier (NAI), containing the IMSI. This message is encrypted.
      • But an attacker intercepting traffic to the UNC-SGW could act as a false UNC-SGW and receive the NAI of the Mobile Station before it has to authenticate itself as a valid UNC. This information could be used to locate a mobile subscriber, hence violating the subscriber identity. This identity probing is a known issue caused by the IKEv2 protocol
    • Dos attack:
      • Before the responder authenticate the initiator,the responder will compute DH agreed key (指數運算),so the attacker can make a lot of request to build IKE SA.
uma security analysis1
UMA Security Analysis
  • Open Platform
    • Unauthorized access and identity spoofing
      • By virus or Trojan horse
    • Exploitation of implementation weakness
      • Such as buffer overflow
    • Denial of service
      • Attack from WLAN、internet
    • Eavesdropping
    • Location spoofing
protecting against the attack
Protecting against the attack
  • Protecting non-malicious users’ terminals
  • Technical prevention of unapproved terminals
  • Legal prevention of unapproved terminals
  • Detecting and disabling misbehaving terminals
  • Increasing core network resistance to attacks
conclusion future work
Conclusion & Future Work
  • Since the UMA specifications have been published only recently, it is possible that they contain problems with potential security implications.
  • Future work is also required to determine the security impact of UMA in roaming situations, to identify better countermeasures against denial-of-service attacks, and to investigate mechanisms for detecting misbehavior and fraud
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