Researchers develop secure audio captchas

May 2, 2016, Ruhr-Universitaet-Bochum

Many websites require users to prove that they are human by entering symbols that are difficult to read. For partially sighted users, acoustic solutions have been devised. IT researchers aim to improve their quality.

Words are synthetically generated and distorted

Anyone who surfs on the Internet will sooner or later encounter captchas, text boxes with machine-altered letters and symbols, used to distinguish human Internet users from machines. As partially sighted people are unable to read those symbols, an alternative to the graphic captcha is available: the captchas. They consist of synthetically generated and more or less distorted sequence of , letters, or digits that the user has to transcribe using the keyboard.

However, audio captchas often don't work very well. Human have difficulties in solving them, whereas computers often show superior performance on the task, according to IT expert Hendrik Meutzner. Together with Prof Dr Dorothea Kolossa, both from the research group Cognitive Signal Processing at the Institute of Communication Acoustics, he investigates the development of secure audio captchas.

Machine does not distinguish between words and gibberish

One of his captchas makes use of human speech comprehension. It presents a sequence of words to the listener, some of which make sense, while the rest is gibberish. "A human will be able to spot and recognise the meaningful words. The machine will find the task difficult, because the meaningful words and the gibberish sounds exhibit very similar characteristics in the time-frequency domain," says Meutzner.

For that nonsense captcha, the success rate was measured to be 60 per cent; as opposed to 14 per cent in machines. In contrast: an audio captcha currently deployed by a large online search engine is cracked by 63 per cent of the machines, as Meutzner's tests have unveiled.

Explore further: Stanford computer scientists find Internet security flaw

Related Stories

Stanford computer scientists find Internet security flaw

May 24, 2011

(PhysOrg.com) -- Researchers at the Stanford Security Laboratory create a computer program to defeat audio captchas on website account registration forms, revealing a design flaw that leaves them vulnerable to automated attacks.

reCAPTCHA eases up on the human eye

October 28, 2013

(Phys.org) —Google, assuming you are human and reading this, wants you to know that CAPTCHAs are more readable. There will be easier days ahead than having to put your face against the screen, struggling to figure out if ...

CAPTCHA evokes sympathetic (aka correct) response

October 9, 2012

(Phys.org)—CAPTCHAs by definition (stands for Completely Automated Public Turing Test to tell Computers and Humans Apart) are gotcha tools that are used to spot automated-attack attempts posing as people. CAPTCHA programs ...

Google updates hair-pulling CAPTCHA with tick box

December 4, 2014

Google's reCAPTCHA is a free anti-abuse service to protect users' websites from spam and abuse. The good news is that the CAPTCHA test can be tossed for many users, replaced with a simple one-box tick saying you're human, ...

Recommended for you

Pushing lithium ion batteries to the next performance level

December 13, 2018

Conventional lithium ion batteries, such as those widely used in smartphones and notebooks, have reached performance limits. Materials chemist Freddy Kleitz from the Faculty of Chemistry of the University of Vienna and international ...

Uber filed paperwork for IPO: report

December 8, 2018

Ride-share company Uber quietly filed paperwork this week for its initial public offering, the Wall Street Journal reported late Friday.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.