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tesla & snep

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  • Low overhead (1 MAC) Communication (same as SNEP) Computation (~ 2 MAC computations) Perfect robustness to packet loss Independent of number of receivers No digital signature required

spins spins Presentation Transcript

  • SPINS: Security Protocols for SensorSPINS: Security Protocols for Sensor NetworksNetworks By : BHUMIKA SHAH(M.E I.T)
  • OutlineOutline  Introduction to sensor networks -What are sensor network? -Hardware  Security for sensor networks - Research Problem  Proposed Techniques - SPINS building blocks  Applications  Discussion  Conclusion
  • Sensor networksSensor networks Applications: environmental monitoring and disaster prevention building monitoring and automation monitoring the physical conditions of patients (e.g., elderly people)  battlefield Energy consumption is an issue: multi-hop communications in-network processing specially designed protocols sleep mode energy harvesting View slide
  • Hardware specification[1]Hardware specification[1] View slide
  • Is security on sensors possible at all?[1]Is security on sensors possible at all?[1] Memory constraints:- -memory is not enough to store even the variables of standard asymmetric key crypto systems. -standard implementations of symmetric key primitives (ciphers and hash functions) need to be optimized in order to fit in the memory. -available memory may increase in the future (price is still an issue). -some asymmetric crypto systems may require less resources. Processor:- -4 MHz, 8 bit RISC processor, with 32 general purpose registers -limited instruction set • good support for bit- and byte-level I/O operations • lack of arithmetic and logic operations Battery power:- -will remain a crucial limitation for some time -communications consume much more energy than computation -crypto algorithms and PROTOCOLS must be designed and optimized to reduce energy consumption
  • System AssumptionsSystem Assumptions  Communication patterns -Node to base station (e.g. sensor readings) -Base station to node (e.g. specific requests) -Base station to all nodes  Base Station -Sufficient memory, power -Shares secret key with each node  Node -Limited resources, limited trust A B D E F G C Base Station
  • Communication architecture[2,3]Communication architecture[2,3]  RF communications broadcast – easy to eavesdrop messages – easy to inject fake messages – easy to delete messages (jamming) – modification of messages on-the-fly is hard – but: delete – modify - re-inject may work  Typical communication patterns: – many-to-one (nodes to base station) (measurement) – one-to-many (base station to all nodes) (control information)  Nodes can – recognize packets addressed to them (addressing) – handle broadcast messages – forward packets toward the base station (using the routing topology)  The base station can access individual nodes using source routing, if needed
  • Trust setup[1]Trust setup[1]  The base station is trusted by all nodes  Sensor nodes are untrusted – they are unattended – they are not tamper resistant – they can be captured and compromised  RF communication channels are untrusted  Initial keys – each node has a unique key that it shares with the base station – compromise of this key affects only a single sensor  Time synchronization – upper bound on the node ‘s clock drift
  • Security for Sensor Networks[1]Security for Sensor Networks[1]  Data Authentication:- – it is easy to inject fake packets into the network – special requirements of broadcast authentication • symmetric MAC cannot be used • asymmetric digital signatures are not feasible  Data Confidentiality:- – sensor readings might be sensitive, some control data (e.g. keys) must be kept secret – eavesdropping is easy.  Data Integrity:-integrity of sensor readings and control data is important  Data Freshness:-freshness of sensor readings is usually important and replay of old packets is easy – weak freshness • provides partial message ordering, but no delay information • useful for sensor readings – strong freshness • allows delay estimation • required by time synchronization
  • Notation[4]Notation[4]
  • ContributionsContributions SNEP -Sensor Network Encryption Protocol -Secures point-to-point communication µTESLA -Micro Timed Efficient Stream Loss-tolerant Authentication -Provides broadcast authentication
  • Properties of SNEP[1]Properties of SNEP[1]  Semantic security – same messages are encrypted differently each time due to the different counter value  Data authentication and integrity by using MAC  Weak freshness and replay protection – counter is part of the MAC – it ensures message ordering  Low communication overhead – counter is not sent, it is maintained locally by both parties – using the block cipher in CTR mode results in a stream cipher �  Encrypted messages has the same length as plain messages – MAC adds only 8 bytes per message  Reduced computational overhead – MAC verification doesn’t need decryption
  • Key Generation /Setup[4]Key Generation /Setup[4]  Nodes and base station share a master key pre-deployment  Other keys are bootstrapped from the master key: ◦ Encryption key ◦ Message Authentication code key ◦ Random number generator key Counter RC5 Block CipherKey Master KeyMAC KeyEncryption Keyrandom
  • Building blocks: SNEP[1]Building blocks: SNEP[1]  Sensor Network Encryption Protocol (SNEP): A B : encKenc,C(data) | macKmac(C|encKenc,C(data)) where – encKenc,C is encryption in CTR mode with key Kenc and counter C – macKmac is CBC-MAC computation with key Kmac – MAC is computed over the encrypted data and counter C – MAC length is 64 bits – Kenc and Kmac is derived from the master key K (shared by the node and the base station) through a one way function: Kenc = macK(1) Kmac = macK(2)
  • Authentication, Confidentiality[1]Authentication, Confidentiality[1]  Without encryption can have only authentication  For encrypted messages, the counter is included in the MAC  Base station keeps current counter for every node Node A M, MAC(Kmac, M) {M}<Kencr, CA>, MAC(Kmac, CA|| {M}<Kencr, CA>) Node B
  • SNEP with strong freshness[1]SNEP with strong freshness[1] A B : NA, request B A : encKenc,C(response) | macKmac(NA|C|encKenc,C(response)) where – the request can use plain SNEP for confidentiality and authentication – NA is an unpredictable random number computed as NA = macKrnd(S) – after generating a random number, S is incremented by one – Krnd is a key derived from the master key K (shared by the node and the base station) through a one way function: Krnd = macK(3) and regenerated from time to time: Krnd’ = macK (Krnd)
  • Strong Freshness[1]Strong Freshness[1] • Nonce generated randomly • Sender includes Nonce with request • Responder include nonce in MAC, but not in reply Node A Request, NA {Response}<Kencr, CB), MAC(Kmac, NA || CB|| {Response}<encr, CB>) Node B
  • Counter Exchange Protocol[1]Counter Exchange Protocol[1] Bootstrapping counter values Node A CA CB, MAC(Kmac, CA||CB) Node B To synchronize: A →B : CA B →A : CB, MAC(Kmac,CA || CB).
  • Code re-use in SNEP[2]Code re-use in SNEP[2]  Only encryption part of RC5 is implemented  This is used – to encrypt and to decrypt (due to CTR mode) data – to implement the MAC function – to generate encryption and MAC keys from the master key – to generate random numbers
  • Building block:Building block: µµTESLA Authenticated BroadcastTESLA Authenticated Broadcast  Main idea: asymmetry through delayed disclosure of authentication keys – base station computes a MAC with a key unknown to the sensors – base station sends and sensors receive the message with the MAC – later, the base station discloses the key used to compute the MAC  Assumptions: – loose time synchronization between the base station and the sensors – each sensor knows an upper bound on the maximum synchronization error – initial secret between the base station and each sensor to bootstrap the whole mechanism
  • Key Setup[1]Key Setup[1]  Main idea: One-way key chains  K0 is initial commitment to chain  Base station gives K0 to all nodes Kn Kn-1 K1 K0 X ……. F(Kn) F(K1)F(K2)
  • Broadcast[1]Broadcast[1]  Divide time into intervals  Associate Ki with interval i  Messages sent in interval i use Ki in MAC  Ki is revealed at time i + δ  Nodes authenticate Ki and messages using Ki K0 K1 K2 K3 … 0 1 2 3 4 time δ
  • Broadcasting Authenticated Packets[1]Broadcasting Authenticated Packets[1]  In interval j, base station broadcasts Msg  Node verifies that key Kj has not been disclosed yet  Node stores Msg Node A Base Station Tnow, Ki, Ti, Tint, δ, MAC(Kmaster, Nonce | Tnow | …) Nonce Msg, MAC(Kj, Msg)
  • Node authenticating packets[1]Node authenticating packets[1]  After disclosure interval δ, base station broadcasts Kj  Node verifies that F(Kj) = Kj-1, or F(F(Kj)) = Kj-2, etc.  Node verifies MAC of Msg  Node delivers Msg Node A Base Station Tnow, Ki, Ti, Tint, δ, MAC(Kmaster, Nonce | Tnow | …) Nonce Msg, MAC(Kj, Msg) Kj δ
  • Perfect robustness to packet loss[1]Perfect robustness to packet loss[1] K2 K3 K4 K5 tTime 2 Time 3 Time 4 Time 5 K1 P5 K3 P3 K1 P2 K0 P1 K0 Verify MACs P4 K2 FF Authenticate K3
  • µµTESLA PropertiesTESLA Properties  Asymmetry from delayed key disclosure[1]  Self-authenticating keys[1]  Requires loose time synchronization[3]  Low overhead (1 MAC) - Communication (same as SNEP) - Computation (~ 2 MAC computations)  Independent of number of receivers
  • Applications[1]Applications[1] Authenticated Routing Node to Node Agreement A B: NA, A B S: NA,NB, A, B, MAC(K’BS, NA || NB || A || B) S A: {SKAB}KSA , MAC(K’SA,NA || A || {SKAB}KSA ) S B: {SKAB}KSB , MAC(K’SB,NB || B || {SKAB}KSB )
  • Discussion: DrawbacksDiscussion: Drawbacks  The µTESLA protocol lacks scalability[1] - require initial key commitment with each nodes, which is very communication intensive  SPINS uses source routing, so vulnerable to traffic analysis[2,3]
  • Conclusion[1,3]Conclusion[1,3]  Strong security protocols affordable - First broadcast authentication  Low security overhead - Computation, memory, communication  Apply to future sensor networks -Energy limitations persist -Tendency to use minimal hardware  Base protocol for more sophisticated security services
  • ReferencesReferences [1] Adrian Perrig, Robert Szewczyk, Victor Wen, David Culler, J. D. Tygar.”SPINS: Security Protocols for Sensor Networks” [2] International Journal of Advanced Research in Computer Science andSoftware Engineering[Volume- 3, Issue-8, August- 2013] “Emerging Trends in Cryptography” [3] Pritam Gajkumar Shah Lecturer, Telecom Engineering Department RV College of Engineering, Bangalore ” Network Security Protocols for Wireless Sensor Networks-A Survey ” [4] Ali Modirkhazeni, Norafida Ithnin, Mohammadjavad Abbasi” Secure Hierarchal Routing Protocols in Wireless Sensor Networks; Security Survey Analysis ”
  • Thank youThank you