1. Security Of Wireless Networks: How Low-Layers Security Can Help
November 2008
doc.: IEEE /1259r0
November 2008
Security Of Wireless Networks:  How Low-Layers Security Can Help
Date:
Authors:
Alex Reznik, InterDigital
Alex Reznik, InterDigital

2. November 2008
doc.: IEEE /1259r0
November 2008
Abstract
Following up on the authors’ earlier presentation to the WNG (IEEE /0973r0), this contribution reviews the case presented for the need for low-layer security. We then provide additional detail on how low-layer security may be implemented and the potential impact on existing specifications and implementations.
Alex Reznik, InterDigital
Alex Reznik, InterDigital

3. WLANs in the Emerging World
November 2008
WLANs in the Emerging World
Usage
Data (IP) access to a broadband network
Streaming applications over IP (e.g. VoIP, Video)
Interactive local application (distributed gaming)
Localized Mesh network with limited/no extra-net access
Machine-to-Machine communication
Home and Small Enterprise Automation
SensorNet-to-DataNet interaction
Distributed Computation
Security requirements
Secure transmitted data
Access control based on
Pre-shared keys (e.g. WPA)
ID (user and device) based access
Enforce network usage policies
Mesh security without a third-party certificate authority
Ensure network availability
Location-based requirements
The NET
Automation
WLAN
Local
Alex Reznik, InterDigital

4. Moving Forward On Security
November 2008
Moving Forward On Security
Currently existing security components provide:
End-to-end data protection
Limited or non-existing WLAN security components:
Device security
Device/host identity capability
Combined with trusted computing concepts
Location privacy assurance techniques
Local network security
Protect availability/access/usage of the physical medium
Enable location-based policies
These impact all layers of the architecture
Commonly used higher-layer protocols need to be enhanced with existing and new ones (e.g. IETF’s HIP, PBS, etc.)
Security Manager is needed for integration of higher-layer security policies and requirements with transmission medium capabilities
MAC support is required to make existing protocols attack-proof (e.g. CSMA), provide support for higher layer protocols (e.g. PBS, 802.1X-type authentication, etc.) and interface with PHY
PHY is required to monitor the medium, implement protocols as required by MAC
At all levels, services provided by secure platforms (e.g. via TPM) may be required
In this talk:
Concentrate on protection/access/usage of the physical medium
This is directly in scope for : as it inherently relies on PHY and MAC mechanisms
Alex Reznik, InterDigital

5. High-Level Threat Analysis for 802.11
November 2008
doc.: IEEE /1259r0
November 2008
High-Level Threat Analysis for
Authentication
Authorization
Confidentiality
Integrity
Availability
Non
Repudiation
Traffic Analysis ■
Passive
Eavesdropping
Active
Man in the middle
Session
high-jacking
Replay
Unauthorized
Access
Denial of
Service
False Identity
Security
Attribute
Addressed by
802.11i
802.11i +w x √
Threat
Authentication
Ensures that the nodes that are communicating are correctly identified
Authorization
Ensures that the access to the service is according to security policy
Confidentiality
Ensures that data (encrypted or sent in the clear) is only read by the appropriate parties
Integrity
Ensures that data is not modified by any party other than the communicating ones
Availability
Ensures that legitimate users are not denied access to resources (e.g. communication link, network resources, etc.) by invalid users
Non-repudiation
Ensures that a party that sent/received data cannot deny having done so
These vulnerabilities are broad when viewed from a network perspective and are subject to a broad number of different attacks. These are identified (and in part addressed by 802.1), but not by
Alex Reznik, InterDigital
Alex Reznik, InterDigital

6. Addressing the threats in a wireless setting
November 2008
Addressing the threats in a wireless setting
Challenges:
Confidentiality/authentication techniques cannot address DoS attacks aimed at the network itself
802.1AE techniques need to be examined, but are insufficient in a wireless context
Smart Jamming can masquerade as generic interference
Not addressed by 802.1AE as the problem is absent in wired systems
Terminal location is a priori uncertain
No connection to a port that signals can be traced back to
Alternate “secure key source” for confidentiality/authentication of pre i messages is desirable
802.1AE calls for cipher suites which, in principle, do not need to rely on 802.1X
None have been proposed to date
A potential approach for wireless systems
Use the richness of the wireless access medium
Enhance PHY/MAC based security tied to the wireless medium
Enhance existing security mechanism
This is commonly called “PHY Layer Security”
Alex Reznik, InterDigital

7. PHY-Layer Security “PHY-Layer” security may:
September 2008
PHY-Layer Security
“PHY-Layer” security may:
Exploit the physical properties of the wireless channel
Typically have PHY and the MAC aspects
Be complementary to other modern techniques for securing wireless nets
PHY-Layer Security may use the physical link as a non-repudiatable, shared, secret resource to:
Provide always-on, link-specific message stream authentication
Classify interference appropriately (malicious/benign) and apply appropriate counter-measures
Distinguish between co-located and distinctly located terminals
Derive and update secret keys based on link properties and without the need to use (and expose) authentication credentials
PHY-Layer Security may further use link and terminal capabilities to:
Null out an identified rogue terminal
Switch away from channels under attack
Proactively hop channels to confuse attacker
Alex Reznik, InterDigital

8. PHY-Layer Security - Examples
September 2008
PHY-Layer Security - Examples
Example Attack 1: A Low-Power Jammer
Attacking terminal reverses the CSMA process – transmits whenever it detects energy on the channel
Legitimate terminals forced into even increasing back-off
Average power required for the attack is low
Initial power consumption is relative high
After a fairly short period, most terminals are in a long back-off state
The CSMA protocol assists in the attack
Example Attack 2: Sybil Attack
A terminal uses multiple MAC addresses:
Increases it share of bandwidth utilization
Attempts a service specific DoS (e.g. multiple authentication/association requests)
Alex Reznik, InterDigital

9. Example Attack 1: A Low-Power Jammer
November 2008
Example Attack 1: A Low-Power Jammer
Potential Detection and Mitigation:
Detection:
Continual power measurement during channel clear state and burst reception reveal that burst should be successfully received
When this is violated sufficiently often (i.e. we observe statistically “impossible” collision pattern), an attack is likely
If MIMO is present, direction of interference may be estimated and further found to be non-random
Mitigation:
Alert security policy manager to abnormal condition, its nature, and (if possible) approximate localization
Switch channels. If possible establish a dynamic channel hopping policy.
Change the back-off protocol to eliminate increasing the expected back-off time. This will make the attack costly (in terms of energy) and may drain the battery of a true low-power attacker
If MIMO present, null away interference source.
Alex Reznik, InterDigital

10. Ex. 1: Implementation of Detection: in the PHY
November 2008
Ex. 1: Implementation of Detection: in the PHY
Alex Reznik, InterDigital

11. Ex. 1: Implementation of Detection: in the MAC
November 2008
Ex. 1: Implementation of Detection: in the MAC
Comments:
2 minor modifications in PHY
Reporting certain quantities (RSSI and Channel Clear) at all times as opposed to as a result of certain event
A new mechanism for providing this report to PHY is therefore required
No new PHY processing is needed
New MAC processing is added, existing functionality not affected
Alex Reznik, InterDigital

12. Ex. 1: Implementation of Mitigation
November 2008
Ex. 1: Implementation of Mitigation
Notes
Mitigation impacts only the Tx Control SEQR
This involves added functionality only
Currently: single Tx Policy (current CSMA/CD)
New:
a number of policies, of which existing is one
Tx Control/SEQR selects one based on request from Security Manager
No impact in the PHY
Expected for mitigation
Alex Reznik, InterDigital

13. Example Attack 2: Sybil Attack
November 2008
Example Attack 2: Sybil Attack
Potential Detection and Mitigation:
Detection
Using channel-based signatures establish the fact that multiple MAC addresses appear to be from same radio
Mitigation
Alert security policy manager to abnormal condition, its nature, and (if possible) approximate localization
If required by policy, establish that when treated as an aggregate these do not follow the proper protocol for a single terminal
De-associate all MAC addresses with suspect channel signature
If MIMO present, null away transmission from suspect location
Alex Reznik, InterDigital

14. Ex. 2: Implementation of Detection
November 2008
Ex. 2: Implementation of Detection
Notes
PHY Impact:
No new functionality
Reporting of CIR
MAC Impact
Increasing existing address matching functionality to check for signature/address consistency
Addition of “security alert/attribute” to each PDU
As before augmentation, not modification of existing functionality,
Alex Reznik, InterDigital

15. Ex. 2: Implementation of Mitigation
November 2008
Ex. 2: Implementation of Mitigation
Notes
Primary mitigation strategies involve management-level activities
Additional management procedures added to address security needs
PHY-based (MIMO) countermeasures require minor modifications to PHY beamformer
Alex Reznik, InterDigital

16. Observations Detection Mitigation:
November 2008
Observations
Detection
Requires Physical Measurements to be made available …
SW based “detection” algorithms determine alerts
Mitigation:
Requires MAC Control of Parameters of Existing Protocols ….
Enables MAC to encrypt control frames as follows…
New control/man. Frames to support all this???
Alex Reznik, InterDigital

17. Review of Previous Straw Poll Results
November 2008
Review of Previous Straw Poll Results
Do you believe that future systems/applications will require security beyond what currently has?
Yes \ No \ Need more info \ Don’t care: 21 \ 11 \ 2 \ 1
Do you believe that protecting against DOS attacks requires security beyond what currently has?
Yes \ No \ Need more info \ Don’t care: 8 \ 2 \ 18 \ 0
Do you believe that protecting against False Identity attacks requires security beyond what currently has?
Yes \ No \ Need more info \ Don’t care: 6 \ 3 \ 22 \ 0
Should start a study group to address physical layer security?
Yes \ No \ Need more info \ Don’t care: 2 \ 15 \ 17 \ 0
Alex Reznik, InterDigital

18. November 2008
Straw Poll 1
Is detection of attacks like Example 1 and Example 2 desirable for ?
Yes No
Need more info
Don’t care
Alex Reznik, InterDigital

19. November 2008
Straw Poll 2
Is mitigation of attacks like Example 1 and Example 2 desirable for ?
Yes No
Need more info
Don’t care
Alex Reznik, InterDigital