Download Link Layer Security for SAHN Protocols

Muhammad Mahmudul Islam
Ronald Pose
Carlo Kopp
School of Computer Science & Software Engineering
Monash University
Australia
 Problem statement
 Limitations of WEP and 802.11i
 Features of Link Layer Security Protocol (LLSP)
 Overview of LLSP
 Security analysis of LLSP
 Overhead of LLSP
 Future work
 Questions
What is Security
 Authentications, verifies the authenticity of the sender
 Encryption, hides information
 Integrity, prevents unauthorized modification
Security in ad-hoc networks above link layer
 Secure route discovery and route maintenance (e.g. SAR, ARIADNE,
ARAN etc)
 Secure communication on end-to-end basis (e.g. IPSec)
 Monitor traffic pattern and take necessary steps to minimize
malicious/selfish behaviors (e.g. Watchdog, Pathrater, CONFIDANT etc)
Common assumption of these solutions
 A secured layer has already been deployed that securely
distributes various keys, certificates and update information
Link Layer Security Protocol (LLSP) is a solution for
the underlying secured layer
WEP
 Lacks dynamic key management
 One way handshaking, reusing keys and the weaknesses of
RC4 make WEP vulnerable to MITM attacks
 Vulnerable to DoS attacks since association and
dissociation messages are not authenticated
 Not designed for multi-hop ad-hoc networks
802.11i
 Requires a trusted third party authentication server
(RADIUS) for authenticating new nodes
 Uses symmetric keys for authenticating new nodes and
exchanging session keys
 Not designed for multi-hop ad-hoc networks
 Uses capability to flexibly represent the access right and the












identification of each link
Authenticate and encrypt every packet for each link
Guarantee the integrity of information.
Dynamic key management
Reduces replay, MITM and DoS attacks
Not dependent on any trusted third party authentication server
Does not require any MAC-IP binding
Does not need synchronized clocks
Independent of any routing protocol
No network wide flooding of any information
Scales properly with changes in network topology
Does not suffer from initial setup delay for each session
Specially designed for SAHN-like networks







Multi-hop ad-hoc network
Ideal for cooperative nodes, e.g. connecting houses and business
Topology is quasi-static
Uses wireless technology
Multi-hop QoS routing
Decentralized
Multi Mbps broadband
service
 No charges for
SAHN traffic
 Can run alongside
TCP/IP
 Conceived by Ronald Pose & Carlo Kopp in 1997
at Monash University, Australia
Security Services Provided by LLSP
 Type 1: Authenticates a new node
 Type 2: Updates the capability (CAP) of a link
 Type 3: Updates the shared key (SHK) of a link
 Type 4: Authenticates received packets and
 Type 5: Encrypts payload of MAC layer
Authenticate a New Node
Step 1: N gets CAPNO & PBKO from O offline
New node N
O Existing node
Step 2: N generates CAPON, SHKNO & ATHREQ
ATHREQ: [CAPNO , CAPON , SHKNO , SEQNO , SIG] PBKO+
Step 3: ATHREQ
Step 4: [ATHREQ]PVKOO accepts ATHREQ if CAPNO, SIG & SEQNOare valid
Step 5: O generates SHKON & ATHREP
ATHREP: [CAPON, SHKON, SEQON, SIG]PBKN+
Step 6: ATHREP
Step 7: [ATHREP]PVKON accepts ATHREP if CAPON, SIG & SEQON are valid
Update SHK
N
O
Step 1: N generates new SHKON & SHKREQ
SHKREQ: [CAPNO , SHKON , SEQNO , SIG]PBKO+
Step 2: SHKREQ
Step 3: [SHKREQ]PVKOSHKON is updated if CAPNO, SIG & SEQNOare valid
Step 4: O generates SHKACK
SHKACK: [CAPON , SEQON , SIG]PBKN+
Step 5: SHKACK
Step 6: [SHKACK]PVKNN accepts new SHKON if CAPON, SIG & SEQON are valid
Update CAP
N
O
Step 1: N generates new CAPON & CAPREQ
CAPREQ: [CAPNO , CAPON , SEQNO , SIG]PBKO+
Step 2: CAPREQ
Step 3: [CAPREQ]PVKOCAPON is updated if CAPNO, SIG & SEQNOare valid
Step 4: O generates CAPACK
CAPACK: [CAPON , SEQON , SIG]PBKN+
Step 5: CAPACK
Step 6: [CAPACK]PVKNN accepts new CAPON if CAPON, SIG & SEQON are valid
Secure and Authenticate Data packets
N
O
Step 1: Payload: [CAPNO , DATA , SEQNO , SIG]SHKNO+
Step 2: Encrypted Payload
Step 3: [Payload]SHKNOO accepts the Payload if CAPNO, SIG & SEQNO are valid
Various Packet Formats of LLSP
32 bits
32 bits
64 bits
SAHN Node
Password
Id
Id
CAP
1024 bits
Public Key
128 bits
720 bits
48 bits
CAP CAP
SHK,
Pad
SEQ,
SIG
128 bits
Encrypted (1024 bits)
ATHREQ
128 bits
848 bits
48 bits
CAP
SHK,
Pad
SEQ,
SIG
Encrypted (1024 bits)
ATHREP/ATHACK/
SHKREQ/SHKACK
128 bits
848 bits
CAP Padding
48 bits
SEQ,
SIG
Encrypted (1024 bits)
CAPREQ/CAPACK





CAP of a link as a certificate
Encrypting CAP & SIG ensure the authenticity of each packet
SIG ensures integrity
Encrypting SIG and SEQ reduces replay attacks
Updating keys and CAP regularly makes guessing or
recomputing difficult by unauthorized nodes
 DoS attacks by flooding is not propagated, i.e. kept confined
within the neighborhood of the malicious node
Duration of authentication processes with 802.11b and HW supported AES
Authentication Type
Transmission Rate
(Mbps)
Total Duration
(ms)
Type 1
1
69.86
2
67.24
5.5
65.58
11
65.10
1
45.92
2
44.50
5.5
43.60
11
43.34
Any
In real-time using
AES HW
Type 2, Type 3
Type 4, Type 5
Communication Overhead for single pair of node (1/2)
Communication Overhead for single pair of node (2/2)
Communication Overhead for 35 pairs of node (1/2)
Communication Overhead for 35 pairs of node (2/2)
Enhance the effectiveness and robustness of LLSP by
integrating a monitoring system that can detect
malicious/selfish activities of other nodes
Integrate LLSP with channel access mechanisms of other
wireless technologies (e.g. IEEE 802.11e, 802.16) and measure
performance