Secure%20Ad-Hoc%20Network

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Secure Ad-Hoc Network

• Eunjin Jung
• ejung_at_cs.utexas.edu

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What is Ad-Hoc Network?

• Ad-Hoc Network
• Subset of peer-to-peer computing problem
• Sensor network
• Wireless and mobile
• Physically neighboring participants
• No infrastructure

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Truth is

• Ad-Hoc Network relies on
• Base Station
• Offline configuration
• Potential
• Military operation use
• Sensor network
• Pervasive, ubiquitous computing

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Challenges in Ad-Hoc Network

• Mobility
• Restricted computing resource
• Restricted power resource
• Unreliable communication
• Ad-Hoc
• Transient states
• No trustworthy third party
• Often security protocol integrated with others

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Security in Ad-Hoc Network

• Availability
• Sleep Deprivation Torture
• Power consumption is worse than computing or
  network resource consumption, because the device
  cannot recover as soon as the attack finishes
• Jamming
• Spectrum Spread, Frequency Hopping

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Security in Ad-Hoc Network

• Confidentiality
• Easier to passively eavesdrop
• Cannot rely on expensive cryptosystem
• Symmetric key cryptography is used
• Small key, frequent update vs. large key,
  intermittent update

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Security in Ad-Hoc Network

• Authorization
• Network resource
• Inherently vulnerable to bandwidth stealing
• Should reject routing unauthorized packet
• Transient states
• Security associations between principals are
  transient
• Static authorization policy is unfeasible

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Security in Ad-Hoc Network

• Authentication
• Cannot rely on central server
• Neither on public key cryptography
• Should be adaptive to transient authorization
  policy
• Should be swift to renew symmetric key
• Pre-computed certificate
• Threshold cryptography

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Security in Ad-Hoc Network

• Integrity
• Similar to any communication
• Use traditional solution based on symmetric key
• Non-Repudiation
• Based on public/private key cryptography
• Hard to achieve with limited computing resource
• Content with certificates

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Security in Ad-Hoc Network

• Tamper-Resistance
• Security not only on communication, but also on
  its physical status
• Intrusion Detection
• Shares have to be revoked and renewed when
  compromised
• Anonymity
• Hide the identity of the senders and receivers

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Security in mobile network

• AAA properties
• Authentication
• Authorization
• Accounting
• Standard in CDMA2000 packet core network

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Everything comes to

• Proper authentication scheme is the key to solve
  security problem in ad-hoc network
• Hierarchical authentication scheme
• Less mobility, higher in hierarchy
• Multilevel authentication scheme
• Link layerBT01
• Routing layerPSWCT01
• Application layer

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Traditional ways do not work

• Indirect KerberosFG96
• Assuming application-level proxy to delegate
  public key operations
• Base station can do the job if there is one
• Duplicated servers
• Tradeoff between mobility and cost

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Early works may not either

• Authentication protocols for PCS LH95
• offer even non-repudiation
• Assumption of static and high-capability HOME
  base station works with mobile-IP
• Assumption of reliable communication between home
  base station and current one
• Frequent cryptographic operation including public
  key operation on the subscribers side

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SPINS authenticated routing

• streaming authentication
  protocol
• Two-party key agreement protocol
• SNEP(Secure Network Encryption Protocol)
• data confidentiality, two-party data
  authentication, and data freshness
• Key from , further operation on
  SNEP

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SPINS authenticated routing

• Problem
• Assumption on the functionality of base station
• Lack of local operation

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Decentralized solutions

• Emulations of Certificate Authority
• Key agreement based on prior context or offline
  agreement
• Self-organized public key infrastructure

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Shamirs secret sharing scheme

• Interpolating scheme (mgt1)

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What is threshold cryptography?

• (m, n) threshold scheme
• m-out-of-n scheme, secret sharing scheme
• 1 sender(dealer) distributes partial
  secret(shares, shadows) to n participants
• Any m parts put together can retrieve the secret,
  but not less than m
• Perfect for any group of at most m-1 participants

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Threshold Scheme

• Tradeoff between security and reliability
  according to the choice of m and n
• Reliability measure
• Target of denial of service attack n-m1
• Security measure
• Target of compromising m
• Good for distributed authentication

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Emulation of Certificate Authority

• Each entity has a share of group key
• More than m entities can act as a certificate
  authority local operation
• Each entity computes partial certificate out of
  partial secret
• Proactively update shares, and actively revoke
  any compromised ones

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Still problem remains

• Requires collaborative users have to respond
  the partial certificate request anytime.
• Who can be a dealer?
• Shares are given to principals in bootstrap phase
  (still base station?)

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Password based public key infrastructure

• Prior context is assumed, so all participants
  share a weak secret.
• Extending Diffie-Hellman method to agree on
  stronger symmetric key among multi-parties.

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Password based public key infrastructure

• O(n) steps

c1S4
m1
gS1
P(c1gS1bs2S3)
gS1S2S3
m2
m4
gS1S2S3
gS1S2S3
gS1S2
m3
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Password based public key infrastructure

• Need to communicate with all group members and
  select a leader
• Static group assumption

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Self-organized public-key infrastructure

• Each user publishes its own certificate and some
  for others
• Each user maintains certificate repository, some
  issued by itself, rest by others.
• Trust graph each user is a node, and an edge
  (u,v) denotes user u published certificate to v.

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Self-organized public-key infrastructure
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Self-organized public-key infrastructure

• How many certificates should be stored in the
  repository to cover all pairs in the ad hoc
  network? covers 95
• Certificate neighbor may not be available at the
  trust graph construction time
• Tested on PGP trust graphs does that represent
  ad hoc network properly?

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No scheme is perfect yet

• Security issues in ad-hoc networks are converged
  into authentication problem without
  infrastructure, in peer-to-peer manner.
• The burden of CA is reduced, but still we need
  co-ordination