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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


  • Overview of UMA

    • Introduction

    • Background: GSM and GPRS security

    • UMA overview

  • Security Analysis

  • Protecting against the attack

  • Conclusion


  • 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