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Improving SSL warnings

Adrienne Porter Felt

Chrome security team

felt@chromium.org

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THE HOLY GRAIL

​

1. Warn only when under attack

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THE HOLY GRAIL

​

2. Users understand warnings

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THE HOLY GRAIL

​

3. Users follow warning advice

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How can browsers stop crying wolf?

Photo credit: https://www.flickr.com/photos/tambako

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Webmaster mistakes

Real

attacks

HOW I IMAGINED ERRORS

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0%

DEVELOPER

SSL ERRORS,

MEASURED

10%

20%

WWW SUBDOMAIN

SUBDOMAIN

SUBDOMAIN REV

OUTSIDE WILDCARD

UNKNOWN TLD

MULTI-TENANT

LOCALHOST

PRIVATE URL

% OVERRIDABLE SSL ERRORS

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a248.e.akamai.net

Client clock wrong

Captive

portal

Client missing

root certificate

Certificate mis-issuance

Anti-virus software

School or employer

State attacks

Malware

ISP adding advertisements

Gov’t content filter

Expired certificate

FALSE POSITIVE

REAL ATTACK

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a248.e.akamai.net

Client clock wrong

Captive

portal

Client missing

root certificate

Certificate mis-issuance

Anti-virus software

School or employer

State attacks

Malware

ISP adding advertisements

Gov’t content filter

Expired certificate

FALSE POSITIVE

REAL ATTACK

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a248.e.akamai.net

Client clock wrong

Captive

portal

Client missing

root certificate

Certificate mis-issuance

Anti-virus software

School or employer

State attacks

Malware

ISP adding advertisements

Gov’t content filter

Expired certificate

FALSE POSITIVE

REAL ATTACK

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a248.e.akamai.net

Client clock wrong

Captive

portal

Client missing

root certificate

Certificate mis-issuance

Anti-virus software

School or employer

State attacks

Malware

ISP adding advertisements

Gov’t content filter

Expired certificate

FALSE POSITIVE

REAL ATTACK

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a248.e.akamai.net

Client clock wrong

Captive

portal

Client missing

root certificate

Certificate mis-issuance

Anti-virus software

School or employer

State attacks

Malware

ISP adding advertisements

Gov’t content filter

Expired certificate

FALSE POSITIVE

REAL ATTACK

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Blame

the clock

Wrong clocks cause 20% of HSTS errors

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Captive

portals

4.5% of all errors caused by redirects

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Wonky

trust stores

Expired and missing certificates

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Traffic shaping

Throttle or block expensive streaming

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Schools &

employers

Network admins want to filter content

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Traffic

is $$$$$

Monetizing traffic with ads, search, etc.

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Clear-cut

attack

More common than we think?

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define,

identify,

fix

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define,

identify,

fix

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define,

identify,

fix

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define,

identify,

fix

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How do we explain this to users?

Photo credit: https://www.flickr.com/photos/sandras_weeds

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WHAT WE WANT TO CONVEY

​

Threat source: the attacker is on the network, not a malicious website

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WHAT WE WANT TO CONVEY

​

Data risk: the data on foo.com is at risk (and no other data)

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WHAT WE WANT TO CONVEY

​

False positives: be more concerned about errors on well-regarded sites

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  • Non-technical language _
  • Sixth grade reading level _
  • As brief as possible _
  • Specific about risk _
  • Enough information _

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“...the server presented a certificate issued by an entity that is not trusted by your computer’s operating system.”

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“The security certificate presented by this website

was not issued by a trusted certificate authority.”

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...security is

up to date on

your computer

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...security is

up to date on

your computer

I don’t know if my information is safe…

I don’t know what encrypted means

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  • Non-technical language F
  • Sixth grade reading level F
  • As brief as possible B
  • Specific about risk A
  • Enough information A

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“Your connection is not private. Attackers might be trying to steal your information from www.irs.gov (for example, passwords, messages, or credit cards).”

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  • Non-technical language A
  • Sixth grade reading level A
  • As brief as possible A
  • Specific about risk C
  • Enough information D

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Threat source

​

CORRECT

Chrome 37

49%

Chrome 36

38%

Safari

36%

Firefox

39%

IE

39%

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Data risk

​

BANK

ALL

Chrome 37

18%

65%

Chrome 36

18%

62%

Safari

14%

67%

Firefox

20%

69%

IE

19%

51%

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None succeed yet; how do we do better?

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Can we nudge users to heed our advice?

Photo credit: https://www.flickr.com/photos/lara604/

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  • Clear instruction _
  • Attractive preferred choice _
  • Unattractive other choice _

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OLD CHROME SSL WARNING

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OLD CHROME SSL WARNING

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OLD CHROME SSL WARNING

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  • Clear instruction B
  • Attractive preferred choice F
  • Unattractive other choice F

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  • Clear instruction C
  • Attractive preferred choice A
  • Unattractive other choice A

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ADHERENCE

N

30.9%

4,551

32.1%

4,075

58.3%

4,644

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Opinionated design works where text fails

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So in conclusion...

Photo credit: https://www.flickr.com/photos/sandras_weeds

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​

​

TODO LIST

​

  • Warn only when under attack
  • Users understand warnings
  • Users follow warning advice

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Adrienne Porter Felt

felt@chromium.org

In collaboration with...

Mustafa Acer

Alex Ainslie

Alan Bettes

Radhika Bharghava

Sunny Consolvo

Lucas Garron

Helen Harris

​

​

​

Elisabeth Morant

Chris Palmer

Robert W. Reeder

Ryan Sleevi

Parisa Tabriz

Somas Thyagaraja

Joel Weinberger