Transcript TinySec: A Link Layer Security Architecture for Wireless Sensor Networks Seetha Manickam Modified by Sarjana Singh.

TinySec: A Link Layer Security Architecture
for Wireless Sensor Networks
Seetha Manickam
Modified by Sarjana Singh
Overview
 Motivation
 TinySec-Introduction
 Sensor Networks Security threats and Need
for link layer security architecture design
 Design goals
 Tiny sec Design
 Security Analysis of Tinysec
 Performance Evaluation of Tiny Sec
 Conclusion
Motivation
• Sensor networks : Resource constraint
networks – small memories, weak
processors, limited energy.
• Conventional security protocols (802.11b ,
802.15.4 are found to be insecure , adds
lot of overhead (16-32 bytes) ).
• Need for a new security architecture for
sensor networks –TINYSEC.
TINYSEC
• Light weight and efficient generic link layer
security package.
• Developers can easily integrate into
sensor network applications.
• A research platform that is easily
extensible and has been incorporated into
higher level protocols.
Security threats in Sensor Networks
• Use of wireless communications -In a broadcast
medium, adversaries can easily eavesdrop on, intercept,
inject and alter transmitted data.
• Adversaries can Interact with networks from a distance
by expensive radio transceivers and powerful
workstations.
• Resource consumption attacks: Adversaries can
repeatedly send packets to drain nodes battery and
waste network bandwidth, can steal nodes.
• However , these threats are not addressed. Focus is on
guaranteeing message authenticity, integrity and
confidentiality.
Motivation for Link layer security in
Sensor Networks
• End-End security Mechanisms : Suitable only for
conventional networks using end-end communications
where intermediate routers only need to view the
message headers.
• BUT, in Sensor networks In-network processing is done
to avoid redundant messages-Requires intermediate
nodes to have access to whole message packets and
just not the headers as in conventional networks.
..contd..
Motivation for Link layer security in
Sensor Networks
• Why end-end security mechanisms not suitable
for sensor networks?
• If message integrity checked only at the
destination, the networks may route packets
injected by an adversary many hops before they
are detected. This will waste precious energy.
• A link layer security mechanism can detect
unauthorized packets when they are first
injected onto the network.
Design Goals
• Security Goals
• Performance Goals
• Usability Goals
Security Goals
• A link layer security protocol should satisfy
three basic security properties:
• Access control and Message integrity
-prevent unauthorized parties from participating
• Confidentiality
- keeping information secret form unauthorized parties
• Explicit omission: Replay protection
-an adversary eavesdropping a legitimate message sent
between 2 authorized parties and replays it at a some
time later
Performance goals
• A system using cryptography will incur
increased overhead in length of the
message.
• Increased message length results-decreased message throughput
-increased latency
-Increased Power Consumption( Sensor
Networks )
Usability Goals
• Security Platform- Higher level security protocols
can use Tinysec to create secure pair wise
communication between neighboring nodes.
• To reduce the effort, TinySec should provide
proper interfaces
• Transparency- Should be transparent to the user
• Portability- Should fit into the radio stack so that
porting the radio stack from one platform to
another is easy.
Security Primitives
• Message Authentication code
- A cryptographic checksum for checking
the message integrity
• Initialization vector (IV)
-A side input to the encryption algorithm.
- Provides Semantic Security
TINYSEC-DESIGN
Two Security Options
1.Authentication Encryption (Tinysec-AE)
2. Authentication only (Tinysec-Au)
• Encryption :
 Specifying the IV format
 Selecting an encryption Scheme( CBC)
Tinysec IV format
• IV too long- add
unnecessary bits to the
packet
• Too short – Risk of
repetition
• How long should be the
IV? N bit IV repeat after
2^n +1. If we use a n bit
counter repetitions will
not happen before that
point.
Encryption schemes
• CBC is the most appropriate scheme for sensor
networks –why?
• Works better with repeated IVs.
• IVs can be pre encrypted for use since it is
proved that CBS mode is highly secure with non
repeated IVS.
• One drawback- Message expansion 
• Use Cipher text stealing-Cipher text
length=plaintext length
TinySec packet Format
Security Analysis of TinySec
Message Integrity and Authenticity
• Security of CBC-MAC is proportional to the length of the
MAC.
• Is the choice of 4 byte MAC- less secure then? – NO!!!!!
..Not for sensor networks!
• Given 4 byte MAC- adversary should make at least 2^31
tries. Even if the adversary flood the channel, he can
send only 40 forgery attempts/sec, sending 2^31 would
take 20 months. Battery operated nodes do not have that
much energy to collect all those packets.
Confidentiality analysis for Tinysec
• Combination of carefully formatted IVs ,
low data rates and CBC mode for
encryption achieves high confidentiality in
TinySec.
• The format of the last 4 bytes –maximizes
the number of packets each node can
send before there is a repetition of IV.
• For a network of n nodes, n.2^16 packets
will be sent before the reuse of IV.
Keying Mechanisms
• Appropriate keying mechanism for a
particular network depends on several
factors.
• Tinysec key- A pair of skipjack key-one for
authentication, one or encryption.
• Simplest keying mechanism: Use a single
key for the entire network, Preload the key
before deployment.-Adversary can
compromise on node and get the key..
Keying mechanism –contd.
• Use per-link keying, separate Tinysec key
for each pair of node wishing to
communicate. Drawback: Key distribution
becomes a challenge.
• Allow a group of nodes to share a TinySec
key rather than each pairs. Group keying
provides an intermediate level of
resilience.
Implementation of TinySec
•
•
•
•
Implemented on Berkeley sensor nodes.
Integrated into TOSSIM simulator.
3000 lines of nesC code.
TinyOS 1.1.2 radio stack modified to
incorporate TinySec.
• Level of protection can be included in
the data payload.
Performance Evaluation of TinySec
• Increases the computation costs and the
energy cost of sending a packet, but these
costs must be modest compared to the
security that Tinysec provides.
Cipher Performance
Energy Costs
Throughput
Performance summary
• The energy, bandwidth and latency
overhead –all are less than 10% by using
Tinysec.
• Overhead-due to the increased packet
size for cryptography.
• Tinysec is very competitive with other
solutions.
• Tinysec has gathered a number of external
users.
Conclusions
• We have learnt that there are design
vulnerabilities in the conventional
protocols for sensor networks.
• Conventional protocols tend to be
conservative in their security guarantees,
typically adding 16-32 bytes of overhead.
• Tinysec addresses these with extreme
careful design and takes advantages of
the limitations of sensor networks.
References
Source :
http://www.ece.mtu.edu/ee/faculty/cchigan/EE59
70-Seminar/TinySec.ppt