REVISITING DEFENSES AGAINST LARGE SCALE ONLINE PASSWORD GUESSING ATTACKS
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REVISITING DEFENSES AGAINST LARGE SCALE ONLINE PASSWORD GUESSING ATTACKS. Mansour Alsaleh,Mohammad Mannan and P.C van Oorschot . CONTENTS INTRODUCTION PGRP COOKIES Vs IP ADDRESS COMPARISON WITH OTHER ATT BASED PROTOCOLS LIMITATIONS EMPIRICAL EVALUATION CONCLUSION.

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REVISITING DEFENSES AGAINST LARGE SCALE ONLINE PASSWORD GUESSING ATTACKS

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Revisiting defenses against large scale online password guessing attacks

REVISITING DEFENSES AGAINST LARGE SCALE ONLINE PASSWORD GUESSING ATTACKS

Mansour Alsaleh,Mohammad Mannan and P.C van Oorschot


Revisiting defenses against large scale online password guessing attacks

  • CONTENTS

  • INTRODUCTION

  • PGRP

  • COOKIES Vs IP ADDRESS

  • COMPARISON WITH OTHER ATT BASED PROTOCOLS

  • LIMITATIONS

  • EMPIRICAL EVALUATION

  • CONCLUSION


Revisiting defenses against large scale online password guessing attacks

  • INTRODUCTION

  • Online guessing attacks are commonly observed against web applications and SSH logins

  • Automated Turing Tests-Limits the number of guesses from a single machine.

  • Focus on reducing user annoyance by challenging users with fewer ATTs and subjecting bot logins to more ATTs.

  • Introduces a new protocol called password guessing resistant protocol.

  • PGRP make use of both cookies and IP address.


Revisiting defenses against large scale online password guessing attacks

AUTOMATED TURING TEST


Revisiting defenses against large scale online password guessing attacks

PASSWORD GUESSING RESISTANT PROTOCOL

FLOWCHART

START

Un,pw,cookie,W,FT,FS

If

F 1

B

NO

YES

A


Revisiting defenses against large scale online password guessing attacks

B

A

NO

NO

If

F2

If

F3

FS[srcIP,un]=FS[srcIP,un]+1

YES

ATTchallenge incorrect

If

F4

YES

YES

NO

FS[srcIP,un]=0

Add srcIP to W

FS[srcIP,un]=0

Add srcIP to W

YES

FT[un]=FT[un]+1

If

F5

NO

If

f6

Un,pw is incorrect

ATT challenge is incorrect

NO

Else


Revisiting defenses against large scale online password guessing attacks

F2—((Valid(cookie,un,k1,true)V((srcIP,un) c w))

(FS[srcIP,un]<k1))

(FT[un]<k2)

F3—(ATTChallenge()=pass)

F4—((Valid(cookie,un,k1,false)V((srcIP,un) c w))

(FS[srcIP,un]<K1)

F5—(validUsername(un)

(FT[un]<k2)

F6—(ATTChallenge()=pass)

F1—LoginCorrect(un,pw)


Revisiting defenses against large scale online password guessing attacks

COOKIES Vs IP ADDRESS


Revisiting defenses against large scale online password guessing attacks

  • PGRP make use of both IP address and cookies to minimize user inconvenience during login process.

  • PGRP uses text based CAPTCHA.


Revisiting defenses against large scale online password guessing attacks

  • DECISION FUNCTION FOR REQUESTING ATTs

  • The decision to challenge the user with an ATT depends on two factors:

  • 1) whether the user has authenticated successfully from the same machine previously.

  • 2) The total number of failed login attempts for a specific user account.

  • USERNAME PASSWORD PAIR IS VALID

  • The user wont be asked to answer an ATT challenge if

  • valid cookie is received and FS[srcIP,un] is less than k1

  • IP address is in white list and FS[srcIP,un] is less than k1

  • FT[un]<k2


Revisiting defenses against large scale online password guessing attacks

  • USERNAME PASSWORD IS INVALID

  • User wont be asked to answer ATT challenge if

  • valid cookie is received and FS[srcIP,un] is less than k1

  • IP address is in white list and FS[srcIP,un] is less than k1

  • FT[un]<k2

    OUTPUT MESSAGES

    PGRP shows messages in case of

  • incorrect {username,password} pair

  • incorrect answer to the ATT challenge.


Revisiting defenses against large scale online password guessing attacks

  • WHY NOT TO BLACKLIST OFFENDING IP ADDRESSES?

  • List may consume considerable memory.

  • Legitimate users from blacklisted IP address could be blocked


Revisiting defenses against large scale online password guessing attacks

  • COMPARISON WITH OTHER ATT BASED PROTOCOLS

  • SECURITY ANALYSIS

  • SINGLE ACCOUNT ATTACKS

    Based on 4 questions:

    Q1. What is the expected number of passwords that an adversary can eliminate from the password space without answering any ATT challenge?

    Q2. What is the expected number of ATT challenges an adversary must answer to correctly guess a password?

    Q3. What is the probability of a confirmed correct guess for an adversary unwilling to answer any ATT?

    Q4. What is the probability of a confirmed correct guess for an adversary willing to answer c ATTs?


Revisiting defenses against large scale online password guessing attacks

  • FINDINGS:

  • PGRP provides improved security over PS and VS protocols.

  • Identical security with Strawmann protocol.


Revisiting defenses against large scale online password guessing attacks

  • MULTIACCOUNT ATTACKS

    Based on 2 questions

    Q1. What is the probability that an adversary knowing m usernames can correctly guess a password without answering any ATT challenge?

    Q2. What is the probability of a confirmed correct guess for an adversary knowing m usernames and willing to answer c ATTs?


Revisiting defenses against large scale online password guessing attacks

  • USABILITY COMMENTS ON ATT CHALLENGES

  • Different scenarios:

  • First time login from an unknown machine.

  • Subsequent login from a known machine

  • Valid password is provided

  • Invalid password

  • Invalid Username


Revisiting defenses against large scale online password guessing attacks

  • SYSTEM RESOURCES

  • No list maintained in PS protocol

  • FT is maintained in VS protocol

  • Information of generated cookie is maintained in all three protocols

  • Most expensive operation is generating ATTs

  • PGRP maintains W,FS,FT


Revisiting defenses against large scale online password guessing attacks

LIMITATIONS


Revisiting defenses against large scale online password guessing attacks

  • EMPIRICAL EVALUATION

  • DATA SETS

    Analysis based on 2 datasets.

  • SSH Server log

  • EMAIL Server log


Revisiting defenses against large scale online password guessing attacks

  • ANALYSIS OF RESULT

  • Done on different perspective.

  • The no of successful login attempts—Larger the ratio of successful login without answering ATT to total successful login,the more convenient is user experience.

  • The no of unique usernames in successful logins—Less no of valid users were asked to answer the ATT in PGRP

  • The no of failed login attempts with valid usernames—Less in PGRP

  • The no of unique valid usernames in failed logins–Large decrease in case of PGRP

  • The no of failed login attempts with invalid usernames—In PGRP,it triggers ATTs


Revisiting defenses against large scale online password guessing attacks

  • CONCLUSION

  • PGRP is more restrictive against brute force and dictionary attacks

  • Provide more convenient login experience

  • Suitable for large and small no of organisations


Revisiting defenses against large scale online password guessing attacks

REFERENCES

[1] Amazon Mechanical Turk. https://www.mturk.com/mturk/,

June 2010.

[2] S.M. Bellovin, “A Technique for Counting Natted Hosts,” Proc.

ACM SIGCOMM Workshop Internet Measurement, pp. 267-272,

2002.

[3] E. Bursztein, S. Bethard, J.C. Mitchell, D. Jurafsky, and C.

Fabry, “How Good Are Humans at Solving CAPTCHAs? A

Large Scale Evaluation,” Proc. IEEE Symp. Security and Privacy,

May 2010.


Revisiting defenses against large scale online password guessing attacks

THANK YOU


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