pASSWORD tYPOS and How to Corrent Them Securelychatterjee/ppts/pwtypos...pASSWORD tYPOS in one slide...
Transcript of pASSWORD tYPOS and How to Corrent Them Securelychatterjee/ppts/pwtypos...pASSWORD tYPOS in one slide...
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pASSWORD tYPOSand How to Correct Them Securely
R. Chatterjee, A. Athalye, D. Akhawe, A. Juels, T. Ristenpart
To typo is human; to tolerate, divine.
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rahul
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Password-based authentication systems
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Password459!
Salted, slow cryptographic hash
H(Password459!) = “a5idoiaU7p..”?
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Password-based authentication systems
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Password459!
Salted, slow cryptographic hash
H(Password459!) = “a5idoiaU7p..”?
password459!
H(password459!) = “a5idoiaU7p..”?
Any typo is rejected
Typo-tolerant password checkingAllow registered password or typos of it
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Typo-tolerant password checking in industry
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Password459! pASSWORD459! password459!
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We know little about password typos
Lots of work on usability of passwords…
[Ur et al. 2012], [Shay et al. 2012, 2014], [Mazurek et al. 2013],[Bonneau, Schechter 2014] [Keith et al. 2007, 2009], [Bard 2007], [Jakobsson et al. 2012]
… but nothing on typo-tolerant password checking.
1. How can we build a typo-tolerant systems?
2. How much would tolerating typos help users?
3. Does it endanger security?
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Our work
We measure password typos at Dropbox and show they are a huge problem for both users and service providers.
We develop approaches to typo-tolerant checking, and show they improve utility with minimal security impact.
“Have your cake and eat it too”
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How to do typo-tolerant password checking?
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We focus on relaxed checkers
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Password459!password459!
H(password459!) = “a5idoiaU7p..”?
H(PASSWORD459!) = “a5idoiaU7p..”?
H(Password459!) = “a5idoiaU7p..”?
Apply caps lock
corrector
Apply first case
flip corrector
… …
Slow hash
No change in
password hash
database
Can we find a small but useful set of typo correctors?
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Capslock11%
Flip first letter case4.5%
Add char. at end4.6%
Add char. at front1%
Last digit to symbol
0.2%
Other78.8%
% of all typos
MTurk password transcription study
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Top 320%
100,000+ passwords typed by 4,300 workers
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Impact of top-3 typos in the real world
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Instrumented production login of Dropbox to quantify typos
NOTE: We did not change authentication policy.
24 hour period:
• 3% of all users failed to login because one of top 3 typos
• 20% of users who made a typo would have saved at
least 1 minute in logging into Dropbox if top 3 typos are
corrected.
Allowing typos in password will add several
person-months of login time every day.
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Typo-tolerance will significantly
enhance usability of passwords.
Can it be secure?
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Threat #1: Server compromise
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Password459!password459!
H(password459!) = “a5idoiaU7p..”?
H(PASSWORD459!) = “a5idoiaU7p..”?
H(Password459!) = “a5idoiaU7p..”?
No change in
password hash
database
No change in
security in case of
server compromise
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Threat #2: Remote guessing attack
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password
H(password) = “a5idoiaU7p..”?
H(PASSWORD) = “a5idoiaU7p..”?
H(Password) = “a5idoiaU7p..”?
Apply caps lock
corrector
Apply first case
flip corrector
Apply extra char.
at end corrector
H(passwor) = “a5idoiaU7p..”?
Web service should lock account after 𝑞 wrong guesses.
Get 3 free checks with every query.
⇒ 𝑞 queries result in 3𝑞 free password guesses.
⇒ Previously, 𝑞 queries result in no free guesses
⇒ Attacker’s success increases by 𝟑𝟎𝟎%
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Passwords are not uniformly distributed!
300% improvement, only if all checked passwords are
equally probable.
BUT, humans do not chose random passwords.
Pro
bab
ility
Passwords
Good for online guesses,
maximizes success probability
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Attack simulation using password leaks
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Adversary knows:
Distribution of passwords, and the set of correctors (Top 3)
2.75
0.79
2.94
0.96
0
0.5
1
1.5
2
2.5
3
3.5
phpbb myspace
Succ
ess
pro
bab
ility
(%
) Exact checkingTypo-tolerant checking
Exact checking
Query most probable 𝑞 passwords
Typo-tolerant checking
Query 𝑞 passwords that maximizes
success. Computed using greedy algo.
𝑞 = 10
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passwordPassword
Security-sensitive typo correction
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Don’t check a correction if the resulting
password is too popular.
Free Correction TheoremFor any non-uniform password distribution, set of
correctors, and adversarial query budget 𝑞, there exists a
typo correction scheme that corrects typos with no
degradation in security.
pASSWOR
PASSWORD
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Security of checkers with filtering
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Correct typo ensuring that total probability of all
checked password is less than Pr[𝑝𝑤𝑞].
Estimated password distribution with rockyou
2.75
0.79
2.94
0.96
2.77
0.81
0
0.5
1
1.5
2
2.5
3
3.5
phpbb myspace
Succ
ess
pro
bab
ility
(%
)
Exact checking Typo-tolerant checking
Typo-tolerant checking w/ filtering𝑞 = 10
Change in success: 0.02%
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Typo-tolerant checking can enhance users’ experience for essentially no degradation in security.
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pASSWORD tYPOS in one slide
1. Introduce typo-tolerant password checkers• Compatible with existing password databases, easy to deploy
2. Study password typos empirically• 3% of users fail to login due to correctable, top-3 typos
3. Analyze security of typo-tolerant checkers• “Free” correction theorem (In theory)
• With heuristic, works in practice too
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Thanks! [email protected]
/rchatterjee/mistypography
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