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

Secure Human-Computer Identification against Peeping Attacks (SecHCI): A Survey. Shujun Li , Harry Shum Visual Computing Group Microsoft Research Asia Sep. 2002. Outline. Introduction A User Study SecHCI: General Model SecHCI: A Comprehensive Survey SecHCI: Other Related Works

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

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  1. Secure Human-Computer Identification against Peeping Attacks (SecHCI): A Survey Shujun Li, Harry Shum Visual Computing GroupMicrosoft Research Asia Sep. 2002

  2. Outline • Introduction • A User Study • SecHCI: General Model • SecHCI: A Comprehensive Survey • SecHCI: Other Related Works • Our Opinions

  3. 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

  4. 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 / …

  5. 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

  6. 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

  7. 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.

  8. 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

  9. 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?

  10. 1.4 Solutions to Peeping AttackSecHCI • Matsumoto-Imai protocol proposed at EuroCrypt’91 • Not secure enough, cryptanalyzed by C.-H. Wang et al. at EuroCrypt’95 • Matsumoto protocols proposed at HCI International’95 and ACM CCS’96 • Security against peeping attack is not strong • Hopper-Blum protocols proposed at AsiaCrypt’2001 • 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 AsiaCrypt’2001 paper.

  11. 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

  12. 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 > usability, but they always forget this principle in the real world.

  13. 2. A User Study2.1 Investigation Results (2) • Fixed passwords II • All users have two or more different passwords • Most users have <=6 different passwords • Most users use 6~10-length passwords • Most users also think 6~10 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, 6~10-length passwords are good, and >16 length is unendurable.

  14. 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.

  15. 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 <= 1 minute.

  16. 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 <H(x), C(y)>, which is in the set {accept, reject, }, where  means H find C is a fake verifier.

  17. 3. SecHCI: General Model3.2 What is SecHCI? • Completeness • A HCIP is complete if Pr[<H(z),C(z)>=accept]1-Pc. • Soundness • A HCIP is sound if Pr[<H(x),C(y)>=accept]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.

  18. 3. SecHCI: General Model3.3 Definitions of Security • (p, k)-security against passive peeping attack • Pr[<A(Tk(H(z),C(z))), C(z)>=accept]p, where Adenotes adversaries observe k random sampled identifications. • (p, k)-security against active peeping attack • Pr[<A(Tk(H(z),C(z))), C(z)>=accept]p, where Adenotes adversaries observe k chosen identifications. • (q, k)-human sensitivity (consciousness) to fake verifiers • Pr[<H(z),C(z,A(Tk(H(z),C(z))))>=]1-q, where C(z,A(Tk(H(z),C(z)))) denotes the fake verifier by A.

  19. 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

  20. 4. A Comprehensive Survey4.1 Matsumoto-Imai Protocol • Matsumoto-Imai protocol [EuroCrypt’91] • 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}, W=3124. 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 i=1~, af(i)=W(i).

  21. 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. EuroCrypt’95] • 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.

  22. 4. A Comprehensive Survey4.2 Matsumoto Protocols • Matsumoto Protocol 0 [ACM CCS’96] • Fs is a finite field of order s. • The password is u vectors k1~ku, 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 i=1~u, ai=qiki, the user is accepted. • Matsumoto Protocol 1 and 2 [ACM CCS’96] • Non-essential variants of Protocol 0.

  23. 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 Matsumoto’s paper. • Security Issues • To break the password, only O(u) observations are needed for both passive and active peeping attack.

  24. 4. A Comprehensive Survey4.3 Hopper-Blum Protocols • Hopper-Blum Protocol 1 [AsiaCrypt’2001] • The password is a (0,1)-vector x{0,1}n whose weight is k. • The challenge is also a (0,1)-vector c{0,1}n. The response r is 0 or 1. • For total m challenge, if r=cx holds for at least (1-)m challenges, the user is accepted.

  25. 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.

  26. 4. A Comprehensive Survey4.3 Hopper-Blum Protocols • Hopper-Blum Protocol 2 [AsiaCrypt’2001] • 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.

  27. 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.

  28. 4. A Comprehensive Survey4.4 HumanOIDs@CMU • HumanAut@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.

  29. 4. A Comprehensive Survey4.4 HumanOIDs@CMU • PhoneOIDs@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.

  30. 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.

  31. 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.

  32. 5. Other Related Works5.2 CAPTCHAs • Distorted texts based CAPTCHAs • Gimpy@CMU • Another Gimpy-like CAPTCHA@AltaVista • Pessimal print • Visual pattern based CAPTCHAs • Bongo@CMU • Image based CAPTCHAs • PIX@CMU • CAPTCHAs based on image search problem • More image processing techniques can be used to distort involved images

  33. 5. Other Related Works5.2 CAPTCHAs • Sound/Speech based CAPTCHAs • Sounds@CMU • Byan@CityUHK • Text-only CAPTCHAs • Impossibility of text-only CAPTCHAs under six assumptions • “Find the Bogus Word” • Chinese CAPTCHAs?

  34. 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.

  35. 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?

  36. 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) P=>V: a public (random) witness; 2) V=>P: a (random) challenge; 3) P=>V: a response (dependent on the witness and the challenge).

  37. 6. Our Opinion on SecHCI6.1 A Comparison • By security against passive peeping attack • Matsumoto-Imai Protocol < Matsumoto Protocols < Hopper-Blum Protocol 2 < Hopper-Blum Protocol 1; • By security against active peeping attack • Matsumoto-Imai Protocol < Matsumoto Protocols < Hopper-Blum Protocol 1 < Hopper-Blum Protocol 2; • By usability • Hopper-Blum Protocol 2 < Matsumoto-Imai Protocol < (0,1)-version of Hopper-Blum Protocol 1  decimal version of Hopper-Blum Protocol 1  Matsumoto Protocols.

  38. 6. Our Opinion on SecHCI6.2 Our Opinion • Three principles • Intentional errors • Redundancies • Balance • Two desired requirements • The password length <= 16 • The identification time <= 1 minute.

  39. 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{0,1}n whose weight is k. • The challenge is 2m (0,1)-vectors c1,…,c2m{0,1}n. The response is 2m bits r1,…r2m. • If i=1~m, (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.

  40. Thanks for watching!

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