Secure Human-Computer Identification against Peeping Attacks (SecHCI): A Survey

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Secure Human-Computer Identification against
Peeping Attacks (SecHCI) A Survey

• Shujun Li, Harry Shum
• Visual Computing GroupMicrosoft Research Asia
• Sep. 2002

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Outline

• Introduction
• A User Study
• SecHCI General Model
• SecHCI A Comprehensive Survey
• SecHCI Other Related Works
• Our Opinions

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1. IntroductionOutline

• Human-Computer Identification
• Problems of Widely-Used Fixed Passwords
• Yet Another Danger Peeping Attack
• In the real world
• In the theoretical world
• Known Solutions to Peeping Attack

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1.1 Human-Computer IdentificationThree
Identifications

• Knowledge-based What do you know?
• Fixed (textual/visual) password / PIN
• Pass-phase / Pass-algorithm / word-association
• Challenge-response identification protocol
• Zero-knowledge identification protocol
• Token-based What do you have?
• Magnetic-striped card / Smart card
• Hand-held one-time password generator
• Biometrics-based Who are you?
• Face / Fingerprint / Iris /

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1.1 Human-Computer IdentificationThree
Identifications Comparison

• Knowledge-based
• Fixed Password Easily understood and widely
  accepted, but vulnerable to dictionary attack and
  replay attack
• Challenge-response protocol Relatively complex
  but secure against replay attack
• Token-based
• More secure than fixed password
• You must physically have it / sensitive to loss
• Biometrics-based
• Always with you / minimal user efforts
• Performance is not really satisfactory / privacy
  involved

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1.2 Problems of Fixed Password

• Dictionary attack A troublesome paradox between
  security and usability
• Humans always select passwords from a
  dramatically small subset of the password space
• Too random or too long passwords are hard to
  remember for humans
• Compulsive password rules are useful to avoid
  problems, but users always try to circumvent the
  rules
• Partial solutions Limitations still exist
• Pass-phrases / Pass-algorithms / Word
  associations /
• Visual/graphical passwords

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1.3 Peeping AttackIn the Real World

• Your friends standing behind your shoulders can
  observe your password
• Your adversaries can install hidden cameras to
  steal your password
• Your adversaries can deploy malicious programs in
  your computer to get your password
• Powerful enemies can use TEMPEST (compromising
  emanations) devices to monitor your computer
• A lot of real stories on peeping attacks to
  banking cards (on ATMs) were reported by R. J.
  Anderson in 1994.

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1.3 Peeping AttackIn the Theoretical World

• SecHCI means such a human-computer identification
  by which one can successfully prove its identity
  without any auxiliary devices and via insecure
  communication channel.
• Two kinds of peeping attacks
• Passive peeping attack and Active peeping attack
• In passive peeping attack, adversaries can only
  passively observe the identification procedure
• In active peeping attack, adversaries can impose
  the verifiers
• Open peeping attack and Hidden peeping attack
• One more requirement
• Human sensitivity (consciousness) to faked
  verifiers

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1.4 Solutions to Peeping AttackNon-SecHCI

• Displaying on the screen instead of
  plain-password
• Shielding your input from malicious eyes.
• Visual shielding / TEMPEST shielding
• LVSVSS a shielding based on visual cryptography
• One-time passwords
• Challenge-response protocols
• Biometrics?

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1.4 Solutions to Peeping AttackSecHCI

• Matsumoto-Imai protocol proposed at EuroCrypt91
• Not secure enough, cryptanalyzed by C.-H. Wang et
  al. at EuroCrypt95
• Matsumoto protocols proposed at HCI
  International95 and ACM CCS96
• Security against peeping attack is not strong
• Hopper-Blum protocols proposed at AsiaCrypt2001
• Security against peeping attack is acceptable,
  but the usability is not good.
• PhoneOIDs proposed by M. Blum (2001)
• All proposed PhoneOIDs have been known insure
• HumanAut Project supported by CMU (2002)
• One implementation of a variant of Hopper-Blum
  protocol in AsiaCrypt2001 paper.

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2. A User StudyGoals and Brief Description

• Goals
• Investigate the users opinions on security and
  usability of human-computer identification
  system, especially fixed passwords and SecHCI
• Show the significance of peeping attack and
  SecHCI
• Confirm some principles in the design and
  implementation of human-computer identification
  systems
• Brief description
• A web site is constructed
• 18 questions are involved
• About 100 volunteers attended

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2. A User Study 2.1 Investigation Results (1)

• Fixed passwords I
• Almost all users ever forgot their passwords
• Most users ever told other of their passwords
• Most users think security is more important than
  convenience (usability) after careful
  consideration
• Many users ever encountered hesitation when they
  set a new password
• Some users even have no really secret passwords
• Summary for most users, security gt usability,
  but they always forget this principle in the real
  world.

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2. A User Study2.1 Investigation Results (2)

• Fixed passwords II
• All users have two or more different passwords
• Most users have lt6 different passwords
• Most users use 610-length passwords
• Most users also think 610 is the best password
  length
• Most users think 15 (about) is the upper bound of
  the password length for all security applications
• Summary for most users, 610-length passwords
  are good, and gt16 length is unendurable.

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2. A User Study 2.2 Investigation Results (3)

• Peeping attack
• Most users think peeping attack is a real danger
  in the security world, especially when their
  money and privacy is endangered.
• Most users will follows at least partial warns
  from security experts and technical news.
• Summary the significance of peeping attack is
  confirmed, especially for electronic financial
  applications.

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2. A User Study 2.2 Investigation Results (4)

• SecHCI
• Most users wish the identification procedure can
  be finished within 1 minute
• Most users think security and usability should be
  balanced in the design of secure human-computer
  identification
• Summary a good SecHCI must balance security and
  usability, and the consuming time for one
  identification should be lt 1 minute.

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3. SecHCI General Model 3.1 Fundamentals

• SecHCI should be a challenge-response protocol
  with time-variant parameters like the following
  one.
• Define SecHCI as a HCIP human-computer
  interactive protocol (H,C) with auxiliary input.
  The transcript between H and C is T(H(x), C(y)),
  and the output of the protocol is ltH(x), C(y)gt,
  which is in the set accept, reject, ?, where ?
  means H find C is a fake verifier.

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3. SecHCI General Model3.2 What is SecHCI?

• Completeness
• A HCIP is complete if PrltH(z),C(z)gtaccept?1-Pc.
  
• Soundness
• A HCIP is sound if PrltH(x),C(y)gtaccept?Ps.
• (?, ?, ?)-Human-Only Executability (HOE)
• A HCIP is (?, ?, ?)-human-only executable if any
  T(H(x),C(y)) can be carried by (1-?) population
  with the error probability ?, and can be finished
  within ? seconds.
• A SecHCI is a HCIP satisfying completeness and
  soundness, and (?, ?, ?)-HOE with acceptable
  parameters.

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3. SecHCI General Model3.3 Definitions of
Security

• (p, k)-security against passive peeping attack
• PrltA(Tk(H(z),C(z))), C(z)gtaccept?p, where A
  denotes adversaries observe k random sampled
  identifications.
• (p, k)-security against active peeping attack
• PrltA(Tk(H(z),C(z))), C(z)gtaccept?p, where A
  denotes adversaries observe k chosen
  identifications.
• (q, k)-human sensitivity (consciousness) to fake
  verifiers
• PrltH(z),C(z,A(Tk(H(z),C(z))))gt??1-q, where
  C(z,A(Tk(H(z),C(z)))) denotes the fake verifier
  by A.

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3. SecHCI General Model3.4 Security in the Real
World

• Basic Attacks
• Random response attack (soundness)
• Brute force (exhaustive) attack
• Dictionary attack
• Peeping Attacks
• Store-and-replay attack
• Intelligent off-line password attack
• Differential attack / Deduction-based attack /
  Intersecting attack
• Multi-onlooker peeping attack
• Advanced Attacks
• Partially-known password attack
• Malicious administrator attack
• Denial-of-Logon attack

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4. A Comprehensive Survey4.1 Matsumoto-Imai
Protocol

• Matsumoto-Imai protocol EuroCrypt91
• An simple example to show the basic idea
  ?1,2,,9,0, ?1,2,,8??, the password is
  ?1,2,4,6??, ?1,2,3,4??, W3124. Assume
  ?(?)8 and ?(?)4, the challenge q is a
  bijection from ? to ?, and the response is a
  ?-length word a(a1,,a?) whose characters are
  all in ?. The accepted responses should satisfy
  the following requirement extract all characters
  in q and also in ?, and record their order in q
  to compose a list f(f1,,f?), then ?i1?,
  af(i)W(i).

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4. A Comprehensive Survey4.1 Matsumoto-Imai
Protocol

• Security problems
• Only one observation is enough to know ?.
• This protocol cannot resist replay challenge
  attack (an active peeping attack). Only several
  observations is needed to decrypt ? and then find
  W. C.-H. Wang et al. EuroCrypt95
• In passive peeping attack, the number of
  observations is also rather small.
• C.-H. Wang et al. proposed a modified version,
  but whose usability is too poor.

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4. A Comprehensive Survey4.2 Matsumoto Protocols

• Matsumoto Protocol 0 ACM CCS96
• Fs is a finite field of order s.
• The password is u vectors k1ku, where ki is
  v-dimensional vector in Fsv.
• The challenge is a non-zero v-dimensional vector
  qi in Fsv-0 the response ai is a element in
  Fs.
• If ?i1u, aiqi?ki, the user is accepted.
• Matsumoto Protocol 1 and 2 ACM CCS96
• Non-essential variants of Protocol 0.

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4. A Comprehensive Survey4.2 Matsumoto Protocols

• Usability Issues
• Protocol 1 can make implementations easier.
• Protocol 2 can provide a better trade-off between
  security and usability.
• Some graphical implementations of Protocol 1 and
  2 are given in Matsumotos paper.
• Security Issues
• To break the password, only O(u) observations are
  needed for both passive and active peeping attack.

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4. A Comprehensive Survey4.3 Hopper-Blum
Protocols

• Hopper-Blum Protocol 1 AsiaCrypt2001
• The password is a (0,1)-vector x?0,1n whose
  weight is k.
• The challenge is also a (0,1)-vector c?0,1n.
  The response r is 0 or 1.
• For total m challenge, if rc?x holds for at
  least (1-?)m challenges, the user is accepted.

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4. A Comprehensive Survey4.3 Hopper-Blum
Protocols

• Security Issues
• Hopper-Blum Protocol 1 cannot resist replay
  challenge attack (active peeping attack).
• Some Errors and More Problems
• The result of Theorem 1 is wrong.
• The masquerading probability of random response
  attack is slightly overestimated.
• Paradox exists between security and usability,
  especially on the value of k.

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4. A Comprehensive Survey4.3 Hopper-Blum
Protocols

• Hopper-Blum Protocol 2 AsiaCrypt2001
• Basically, Protocol 2 is similar to Protocol 1
  with two chief modifications.
• Modification 1 the response is calculated with
  sum of k mins.
• Modification 2 the linear error-correcting
  mechanism is introduced to avoid malicious change
  of legal challenges.

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4. A Comprehensive Survey4.3 Hopper-Blum
Protocols

• Merits
• Protocol 2 can resist active peeping attack.
• Protocol 2 has 0.1-human sensitive to fake
  verifiers.
• Problems
• Usability of Protocol 2 is even more poor than
  Protocol 1.
• Some problems in Protocol 1 still exist in
  Protocol 2.

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4. A Comprehensive Survey4.4 HumanOIDs_at_CMU

• HumanAut_at_CMU
• An image-based SecHCI, n images are involved and
  n/2 images compose the password.
• A non-essential variant of Hopper-Blum Protocol
  1. The challenge is always a vector with fixed
  weight.
• Usability is poor when n is too large.
• Pass-Rules
• You can freely change all n images.
• Then you can use some meaningful features of the
  n/2 pass-images to remember so many pictures.

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4. A Comprehensive Survey4.4 HumanOIDs_at_CMU

• PhoneOIDs_at_CMU
• PhoneOIDs is challenge-response protocols for
  use over the phone, which means SecHCI protocols
  of two parties with limited computation
  capabilities.
• Many PhoneOIDs have been proposed, but all are
  insecure.

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5. Other Related Works5.1 Visual/Graphical
Passwords

• Selective pictures based passwords
• PassfaceTM In each round, select your pass-face
  from 9 candidate faces.
• Déjà Vu Select m portfolio images from n
  candidate images.
• Point-and-click passwords
• PassPic Click your pass-positions with your
  pass-order
• Graphical Password Windows in Passlogix v-GOTM
  SSO Click several things to construct your
  password.
• Drawing-based passwords
• Draw-a-Secret (DAS) Draw your pass-strokes on a
  m?n grid.

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5. Other Related Works5.2 CAPTCHAs

• CAPTCHA stands for Completely Automated Public
  Turing Test to Tell Computers and Humans Apart,
  also called Reverse Turing Test by some
  researchers.
• The chief application of CAPTCHA is to foil
  malicious online robots, and can also be used to
  relax the security against random response attack
  in SecHCI protocols.
• The first paper on CAPTCHA occurred in 1996 (by
  M. Naor). The first implementation of CAPTCHA is
  designed in 1997. The initial booming of
  interests on CAPTCHAs is promoted by the
  occurrence of Gimpy, a CAPTCHA designed by M.
  Blum et al. at CMU in 2000. Now a CAPTCHA project
  is supported by Aladdin Center of CMU.

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5. Other Related Works5.2 CAPTCHAs

• Distorted texts based CAPTCHAs
• Gimpy_at_CMU
• Another Gimpy-like CAPTCHA_at_AltaVista
• Pessimal print
• Visual pattern based CAPTCHAs
• Bongo_at_CMU
• Image based CAPTCHAs
• PIX_at_CMU
• CAPTCHAs based on image search problem
• More image processing techniques can be used to
  distort involved images

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5. Other Related Works5.2 CAPTCHAs

• Sound/Speech based CAPTCHAs
• Sounds_at_CMU
• Byan_at_CityUHK
• Text-only CAPTCHAs
• Impossibility of text-only CAPTCHAs under six
  assumptions
• Find the Bogus Word
• Chinese CAPTCHAs?

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5. Other Related Works5.3 More Topics on HIPs

• HIP means Human Interactive Proof, which covers
  many topics, such as SecHCI protocol, CAPTCHA,
  and visual/graphical password.
• There is a HIP project at Aladdin Center of CMU
  to support research and product transfer of
  theoretical results.

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5. Other Related Works5.3 More Topics on HIPs

• Formal Studies on Security and Complexity of HIPs
• Computer Vision and HIPs
• Biometrics
• Visual Cryptography
• Human-Error-Tolerant Passwords (or Fuzzy
  Commitment)
• Other Sides?

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5. Other Related Works5.4 ZK Identification
Protocol

• Many Zero-Knowledge based identification
  protocols have been proposed. The basic idea used
  in ZK protocols may be useful for the design of
  SecHCI protocols.
• The general model of ZK identification protocols
  1) PgtV a public (random) witness 2) VgtP a
  (random) challenge 3) PgtV a response
  (dependent on the witness and the challenge).

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6. Our Opinion on SecHCI6.1 A Comparison

• By security against passive peeping attack
• Matsumoto-Imai Protocol lt Matsumoto Protocols lt
  Hopper-Blum Protocol 2 lt Hopper-Blum Protocol 1
• By security against active peeping attack
• Matsumoto-Imai Protocol lt Matsumoto Protocols lt
  Hopper-Blum Protocol 1 lt Hopper-Blum Protocol 2
• By usability
• Hopper-Blum Protocol 2 lt Matsumoto-Imai Protocol
  lt (0,1)-version of Hopper-Blum Protocol 1 ?
  decimal version of Hopper-Blum Protocol 1 ?
  Matsumoto Protocols.

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6. Our Opinion on SecHCI6.2 Our Opinion

• Three principles
• Intentional errors
• Redundancies
• Balance
• Two desired requirements
• The password length lt 16
• The identification time lt 1 minute.

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6. Our Opinion on SecHCI6.3 A Prototype Protocol

• Following our opinions on SecHCI, we can give a
  prototype protocol as follows
• The password is a (0,1)-vector x?0,1n whose
  weight is k.
• The challenge is 2m (0,1)-vectors c1,,c2m
  0,1n. The response is 2m bits r1,r2m.
• If ?i1m, (r2i-1-c2i-1?x)(r2i-c2i?x)1 (mod 2),
  then the user is accepted.
• Such a protocol may be OK as a new solution of
  SecHCI.

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