Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.

The inaccessibility of CAPTCHA


Published on

How you may be undermining the accessibility of your online service. This presentation explains why current CAPTCHA are inaccessible, discusses some common alternatives and I explain what I think is the best approach for securing online systems whilst still remaining accessible.

Published in: Internet
  • Be the first to comment

The inaccessibility of CAPTCHA

  1. 1. The inaccessibility of CAPTCHA How you may be undermining the accessibility of your online service
  2. 2. What is CAPTCHA
  3. 3. Why use CAPTCHA? • It’s a way to stop bots from compromising your online service – Creating accounts – Spamming users – Commenting on forums
  4. 4. Why use CAPTCHA? • It’s free, fully automated and pretty straight forward to add • Requires no effort to continue using it
  5. 5. How they work • When a challenge is completed correctly the user can continue the task
  6. 6. Problems • CAPTCHA is not accessible – Many are difficult to use via the keyboard • Especially with a screen reader – Very difficult to use if you’re vision impaired – Difficult to understand any audio challenge
  7. 7. Alternatives • Google’s reCaptcha – Users only need to tick an option
  8. 8. Google reCaptcha • Uses a range of criteria to determine humanness – User behaviour on the page – If the user has a Google account
  9. 9. Problem solved? • No – In cases when the risk analysis engine can't confidently predict whether a user is a human or an abusive agent, it will prompt a CAPTCHA to elicit more cues, increasing the number of security checkpoints to confirm the user is valid
  10. 10. Do you feel confident using it? • If you can’t be sure users will never see a CAPTCHA, can you recommend using it? – An accessible website is made inaccessible
  11. 11. Captcha has been compromised • Services exist where people solve in bulk – CAPTCHA farms, using human labour
  12. 12. Background reading • Breaking CAPTCHA – automated-humans/ • Artificial intelligence smart enough to fool Captcha security check –
  13. 13. Other alternatives • Form submission times • Honeypot • Email verification
  14. 14. Form submission times • If a form has been submitted quickly consider it’s been sent by a bot – Ignore the input
  15. 15. Honeypot • Include a hidden form field on the page – If this is filled ignore the input
  16. 16. Email verification • Ask a user to confirm their email address by clicking a link emailed to them
  17. 17. All reasonable responses • Use layered security to improve the security system Email verification Form submission times Honeypot
  18. 18. Other approaches • Asking a user to add two number together • Asking a question
  19. 19. Number CAPTCHA problem • If bots can submit a form, bots can probably work out this
  20. 20. Word CAPTCHA problem • Need to create 100’s of question and answer combinations to ensure they don’t repeat
  21. 21. Besides is this a good look? • Asking trivial questions doesn’t look good on a government website – “what colour is the sky?”
  22. 22. The problem • CAPTCHA is a frontend solution to a backend problem – Why should users have to prove they are human
  23. 23. Most viable alternative • SMS text message • Self declaring on the account signup • Staff assistance if the user is having problems • Application behaviour monitoring
  24. 24. SMS text message • Send a text message with a code before the user can perform a task
  25. 25. SMS text message downside • Can incur significant cost if all users are now receiving a text message – Be discerning and provide the text message option for those who actually require it
  26. 26. Self declaration • Ask if the user requires extra screen reader support – use the SMS text message option instead of CAPTCHA Do you require extra screen reader support?
  27. 27. Self declare downside • Users may not want to self-declare to be identified as different or requiring extra help
  28. 28. Staff assistance • If you can’t avoid CAPTCHA, ensure there is help available – Confirm the user outside of CAPTCHA
  29. 29. Staff assistance example • A link asking the user to contact you if they encounter difficulties If you are having problems contact us
  30. 30. Staff assistance • Can be a suitable stop-gap whilst a long-term strategy for moving away from CAPTCHA is decided – Be pragmatic
  31. 31. Application monitoring • Large number of unused accounts created • Large number of requests from the same IP address – Investigate and block
  32. 32. The trade off • Security and accessibility can co-exist – Except when captcha is used to provide the security
  33. 33. Summary • Current CAPTCHA implementations are not accessible – Some may adhere to certain WCAG 2.0 criteria – Assume all are inaccessible
  34. 34. Summary • The Digital Service Standard advocates user needs and putting the user first – What user need is there for using CAPTCHA? – It’s a business need, not a user need