What is a CAPTCHA and How Do CAPTCHAs Work?
CAPTCHA, an acronym for “completely automated public Turing test to tell computers and humans apart,” is
a technology used to determine whether an online user is a human or a computer program such as a bot. CAPTCHAs were
developed as a type of challenge-response test used in computing to distinguish between human users and automated
bots. Such tests are used to prevent automated spamming, fraud and malicious attacks on websites, as bots in general
cannot solve them with their current level of sophistication without assistance from humans.
What are CAPTCHAs Used For?
CAPTCHAs are used to protect websites and online services from spam and automated attacks by bots. By using a
CAPTCHA, website owners can ensure that only humans, not bots, are accessing their website and using their services.
They also prevent card and payment fraud by only allowing real users to fill out payment pages on websites and
applications.
Examples of how CAPTCHAs are used:
Preventing Ticket Scalping
CAPTCHAs can help prevent ticket scalping by using CAPTCHAs to ensure that only real users are able to
purchase tickets. This can help prevent bots from buying up large numbers of tickets and then reselling them
at inflated prices.
Preventing Fake Comments
Website owners can help prevent fake comments by using CAPTCHAs to ensure that only real users are able to
post comments on a website or forum. This can help prevent spam and other types of unwanted content from
being posted.
Limiting Registrations for Services
Website operators try to prevent fraudulent account registrations by using CAPTCHAs to ensure that only real
human users are able to create accounts. This can help limit the number of fake accounts on a website or
service, which can be further abused for malicious purposes.
Maintaining Poll Accuracy
CAPTCHAs can help maintain the accuracy of online polls by ensuring that only real human users are able to
vote. This prevents bots and automated scripts from skewing the results of a poll or survey.
Securing Payment Processes
Some e-commerce websites and applications have implemented CAPTCHAs on their payment pages. This acts as an
additional step to prevent bots, which use lists of breached or stolen payment card data, from carrying out
transactions. This not only reduces payment fraud but also reduces the likelihood of the merchant being levied fines
by payment processors and potentially having their merchant reputation from being harmed.
How Does a CAPTCHA Work?
A CAPTCHA works by presenting a test or puzzle that is easy for humans to solve but difficult or impossible for bots
to solve. A website presents a CAPTCHA test to the user in the form of an image, audio file, or a simple question
that requires a response. The user completes the test by providing the correct response. This response is then sent
back to the website for verification using advanced algorithms to determine whether the response is likely to have
been provided by a human or a bot. If the response is deemed to be from a bot, the user is denied access to the
website or service.
CAPTCHA Types and Examples
There are several different types of CAPTCHA tests that can be used to determine whether an online user is a human or
a bot. The main types of CAPTCHAs are:
Text-based CAPTCHA
This type of CAPTCHA displays a series of distorted letters or numbers that the user must type into a text box. The
letters or numbers are designed to be difficult for computers to recognize but easy for humans to decipher. Examples
include Google's reCAPTCHA, which features distorted letters and numbers, and Cloudflare's CAPTCHA, which
includes simple arithmetic problems.
Image-based CAPTCHA
This type of CAPTCHA displays an image that contains a specific object or shape, and the user must identify the
object or shape in the image. Image-based CAPTCHAs can be difficult for bots to recognize, as they require advanced
image recognition software. Variations of image-based CAPTCHAs offered by some providers include selecting images of
certain objects from a collage of images, rearranging jigsaw-like images to recreate the original image, rotating
images that the user must click on when it is upright or aligned in a certain way, and similar variations.
Audio CAPTCHA
This type of CAPTCHA is similar to image-based ones but also adds an audio recording. The user listens to a series
of numbers, letters or words and enters them into a text box. These CAPTCHAs can be offered to users with visual
impairments or difficulty completing text-based CAPTCHAs. Many websites use an audio CAPTCHA, which features a
series of spoken letters and numbers.
Math or Word Problems
These CAPTCHAs require users to solve a simple math problem or answer a trivia question to prove that they are
human.
Social Media Sign-in
Some websites use social media sign-in options, such as Facebook or Google, to verify that the user is a real
person. This type of CAPTCHA relies on the assumption that bots are less likely to have social media accounts.
What is the difference between reCAPTCHA and CAPTCHA?
Google’s reCAPTCHA is different from CAPTCHAs in a few ways such as the level of security and the technology
used. “CAPTCHA” is a generic term that refers to any type of challenge-response test that is used to
determine whether a user is a human or a bot. Google developed reCAPTCHA to implement advanced algorithms and
machine learning to determine whether a user is human or not, which is considered more secure than traditional
CAPTCHAs. ReCAPTCHA also includes additional security features such as IP tracking and user behavior analysis to
prevent bots from getting through.
Another key difference between reCAPTCHA and CAPTCHA is the user experience. Traditional CAPTCHAs can be difficult
and frustrating for users to complete. ReCAPTCHA, though, uses a range of interactive tasks, such as image
recognition and mouse tracking, to create a more user-friendly experience. Overall, while both reCAPTCHA and
traditional CAPTCHAs serve the same basic purpose of verifying that a user is human, reCAPTCHA is considered to be
more secure and user-friendly due to its advanced technology and interactive design.
What Are the Alternatives to Using CAPTCHAs?
CAPTCHAs have long been frustrating and inconvenient for many internet users, which is why several alternatives now
provide similar levels of security while also offering a better user experience. Common CAPTCHA alternatives
are:
Honeypots
Honeypots are invisible fields that are added to web forms to detect bots. Human users can't see or interact
with these fields, but bots will try to fill them out, allowing websites to easily identify and block them.
Two-factor Authentication
Two-factor authentication (2FA) is a security process that requires users to provide two forms of identification
before they can access a system or service. This can include something the user knows (such as a password) and
something they have (such as a smartphone or security token).
Behavioral Analysis
Behavioral analysis tools can be used to identify and block bots based on their browsing behavior. This might
include the speed at which they navigate through a website, patterns of mouse and touchpad movements or scrolling
and tapping behavior on smartphones.
Email Verification
Email verification can be used to confirm the identity of a user by sending a verification link or code to their
email address.
Social Media Log-in
Social media log-in can be used to authenticate users and confirm their identity, as many social media platforms
require users to verify their email addresses and phone numbers.
Radware’s Crypto Challenge
Crypto
challenge mitigation is based on the cryptographic proof-of-work concept used in various blockchains and
designed to deliver continuous, invisible browser-based challenges to suspected bots that automatically and
exponentially become more difficult if solved. It uses a challenge-response model that creates a “cyber
counterstrike” by forcing an attacker’s CPU to work harder and longer, thus taking a toll on the
attacker’s resources. Crypto challenge also mitigates sophisticated CAPTCHA-solver and avoider bots.