I've heard of similar systems. The main problem they ran into, as you
pointed out, is they often rely on cultural references and/or good
English parsing skills. The other snag is that even if you come up with
a set of questions that doesn't hit these snags, as a chunk of text the
bad guys can come up with a parser to figure out the question. You
figure if they can come up with algorithims to recognize spoken words,
parsing a sentence to figure out what numbers you want wouldn't be that
much more difficult. Actually, I suspect it would be easier.
This is just a tough nut to crack. The stuff that computers do not do
well is handle fuzzy noisy stuff like blurry image or noisy spoken word
recognition. The very things that make it hard for a human to pass a
cpatcha are the things that protect it from hackers.
CB
Jayson Smith wrote:
A few more thoughts...
I've actually thought of a system which might actually solve this
problem, but it has a few problems of its own. My idea would be to
have the captcha be digits, and to have questions the web visitor must
answer in order to determine those digits. E.G.
Okay, your first digits can be calculated by answering this question.
How many months are in a year? Your next digit is. What's the number
of days in a week? If you have two dozen eggs, what number of eggs do
you have? That's your last set of digits.
In this example, the answer would be 12724. Questions would be
asked deliberately in several different formats in order to confuse
voice recognition systems. There would be many of these questions,
each of which was asked several different ways. To assemble the audio
captcha, you'd take a random subset of these questions.
One problem is that the visitor would have to know good English.
Another issue is that these questions would have to be things which
almost anybody would know. For example, asking for the number of
innings in a baseball game would stump someone who didn't know
anything about that sport.
Jayson
----- Original Message ----- From: "Chris Blouch" <[EMAIL PROTECTED]>
To: "General discussions on all topics relating to the use of Mac OS X
by theblind" <[email protected]>
Sent: Thursday, June 19, 2008 2:05 PM
Subject: Re: Please Join Me In Making Craigslist Accessible Again
Exactly. Just like their visual counterparts, audio captchas are
obfuscated to resist cracking by voice recognition. I know one of the
guys who did one of the voices for AOL's captcha and they had to make
it tougher to keep out the hackers. Hence a random mix of letters and
numbers with different voices and background noise. As I mentioned
before, it's an arms race. As the algorithms of the bad guys get
better the cognitive load required to understand the captcha will
rise to the point where regular folks won't be able to pass the test.
Turing would be impressed.
While we could switch to some other tests they would have to be
sufficiently complex to fool an algorithm while simple enough that a
real human being can solve them and not necessarily require English
as a first language. I haven't seen another better solution yet.
There are some visual ones with random photos and letters where you
have to identify which one is a cat or whatever, but that's not
really accessible.
CB
Jayson Smith wrote:
Some more observations...
On my Windows machine, I acted like I was trying to sign up for
a new account, and it gave me the old-style audio captcha. I went to
post, but don't actually have anything real to post, so didn't go
through with it, so don't know what I'd have gotten.
As for the old audio captcha, assuming it's gone, I'd be
surprised if they go back to it. As I pointed out earlier, the
phonetic words they used are very well known world-wide. I'm sure
these very words were specifically designed so that any one of them
can be distinguished from any other word in that set, E.G. during a
radio transmission in less than optimal signal conditions. Probably
pretty easy for a voice recognition system to crack that.
Jayson
----- Original Message ----- From: "Tiffany D" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Wednesday, June 18, 2008 6:48 PM
Subject: Please Join Me In Making Craigslist Accessible Again
*Please pass this onto any groups or individuals you think could help.
This is serious.
*
Hello to all,
As most of you know by now, many sites use capcha for making posts
etc. Craigslist was always one of the best in this regard. Their
audio was clear and clean, even employing words for letters (a, as in
alpha) to make understanding the codes easier. However, I just logged
in today and when I tried to make a post, I noticed that it didn't
work at all on my Macbook. When I tried posting with my Windows XP
computer, I discovered that their formatting has changed. Not only is
their an extra step to post, but the audio capcha is now similar to
AOL, with many voices speaking at once and it's very difficult to hear
the actual letters in the capcha. I propose creating a petition, to
be signed by all blind and visually-impaired people, as well as other
concerned parties, asking Craigslist to return the capcha to it's
former state and to once again make it Mac and VoiceOver accessible.
While I was posting an add for my personal use, my job also relies
heavily on Craigslist to generate ads and I'm clearly not the only
blind individual using it for this purpose. Please join me in this
effort. The changes are extremely recent and we may be able to stop
this before it becomes permanent.
Thank you,
Tiffany Dunn
