Shulou(Shulou.com)11/24 Report--

"You never know if you're sitting across the net from a person or a dog."

- Netizens joked

Are the users of video, travel, shopping and other websites necessarily human? Could it be a computer disguised as a human?

In order to be able to identify humans and computers,"Captcha" came into being.

Today, let's learn about the past and present lives of Captcha!

01, first understand what is the "Turing test" Since the world's first computer appeared in 1946, intelligent humans have considered the possibility of computer development to replace humans. Alan Matheson Turing, known as the father of computer science and artificial intelligence, designed a famous "Turing test" to determine whether computers can behave indistinguishable from humans in intellectual behavior.

When the host asks a question and can't tell which of the two answers is human and which is computer, it shows that the computer's intelligence level is no longer different from that of humans.

The "Turing test" is for humans to judge: Who is a computer? Who is human?

The most important goal is to identify computers.

02. The reverse "Turing test" is Captcha. Then "Captcha" is judged by the computer: Who is human? Who is the computer?

The most important goal is to identify humans.

This can be seen from the full Chinese and English names of Captcha: CAPTCHA (Completely Automated Public Turing Test to Tell Computers and Humans Apart), also known as HIP (Human Interaction Proof).

The most typical Captcha is shown below.

From the current point of view, this Captcha is indeed a bit crude.

But in an age when computer technology was underdeveloped, such a Captcha was enough to identify humans:

Only humans can recognize severely distorted letters or numbers in Captcha;

The computer cannot recognize it.

Based on such a Captcha, various computer systems (e.g., websites, mailboxes, etc.) successfully identify a real human and allow the human to continue operating, such as logging into mailboxes, voting, etc.

03. Captcha for "protection" Computer technology can also cause problems for humans when various computer systems cannot recognize humans and computers, such as:

Mail box flooding registration, resulting in spam flying everywhere;

Barbaric vote brushing, resulting in unfair voting results;

Tickets plug-in preemption, resulting in return tickets can not be bought.

In 1999, when a website launched an online poll to choose the best computer science schools in the United States, it was technically one vote per person. But voting sites are designed without much consideration, based only on the IP address of the voter's computer.

So someone wrote a computer script to do batch scanning: change an IP address after each vote, and then continue voting. In this case, thousands of IP addresses represent thousands of different people, and thousands of votes can be cast.

Such computer technology undoubtedly affected the fairness of the entire voting.

Therefore, all kinds of computer systems need a strong "shield" to protect themselves.

In fact, the first Captcha (character type) appeared to counter the computer technology of "automatic ticket swiping."

04. More and more solid "shield" So do you know what strange "Captcha" there are?

01. Character type Captcha is the Captcha we see most often every day. It is usually a combination of letters and numbers, and these characters are often distorted, distorted, and flipped to increase the difficulty of recognition.

With the development of computer technology, the security degree of character-type Captcha is decreasing and gradually replaced by other types of Captcha.

02. Computational Computational Captcha, usually mathematical formulas, requires humans to launch intelligent brains to perform complex calculations in order to obtain correct results.

Unfortunately, this kind of Captcha, which can provide high security, is difficult for computers to recognize, but most humans find it difficult themselves. Therefore, computational Captcha has not been widely used.

03. The biggest feature of click-type Captcha is that the user only needs to click with the mouse and does not need to input anything. Through this kind of human-specific behavior, as well as some operation data and browsing data of the user in the browser, the real human can be identified together.

Click-type Captcha has higher security and better user experience.

In some important computer systems, such as bullet train ticketing websites, large shopping websites, large video websites and other places with large number of users and high data security requirements, click-type Captcha can effectively identify human beings and avoid attacks from other computers.

04. Sliding-type sliding Captcha judges whether the user is human by collecting the user's actions. For example, the trajectory of a human dragging a slider will be a fast and slow process: first drag quickly, then align slowly, and then release instantaneously.

The user experience of this kind of Captcha is good. Although the success rate of computer technology breakthrough is more than 60%, the cost of computer technology simulating human behavior is relatively large, and the loss is not worth the loss.

05. SMS SMS Captcha is the most commonly used way. All kinds of App will generally adopt this method, simple and direct, through the operator to send text messages, security is guaranteed.

Each Captcha corresponds to a mobile phone number and is generally valid for only 60 seconds to 90 seconds, leaving no chance for others to exploit the loophole.

06. Code scanning type Captcha, in fact, first ensure that you have successfully logged in on your mobile phone, and then continue to log in on your PC by scanning the QR code. This is a common method used by major video websites and shopping websites today.

Let humans test themselves. Hey, that's great.

07. Biometrics All kinds of Face Recognition, Fingerprint Recognition, Voice Print Recognition and even Iris Recognition can be counted as biometric Captcha. It is simpler to use, and because of the uniqueness of these biological characteristics in each human being, it is like a unique key with high security.

05. More and more sharp "spears" Although "shields" are very strong, with the continuous progress of computer technology, sharp "spears" emerge one after another.

In order to break through the protection of Captcha, the following computer technology has been developed:

OCR technology OCR (Optical Character Recognition) technology can directly convert text content on pictures and photos into editable text.

In 2003, some people automatically recognized simple character Captcha through image recognition algorithm (Shape Context), and the success rate could reach 93%.

OCR technology can only break through some simple character-type Captcha. It takes more time for slightly more complex characters (such as twisting and flipping), and generally cannot be recognized successfully before character-type verification fails.

02. Machine Learning Model In 2005, someone used machine learning model (CNN) to automatically recognize the Captcha of a single character. The recognition success rate of computer was even higher than that of human beings.

However, to use machine learning models to recognize character-type Captcha requires multiple high-performance computers and a large amount of training data, so the cost of model recognition is too high for ordinary people to afford.

03. In order to crack the SMS Captcha, the disguised mobile phone base station needs to first block the signal of the target mobile phone, then try to log in to the website with this mobile phone number, and also be able to disguise the target mobile phone to receive SMS.

Each link has to be completed in a short time. It is simply Mission Impossible. Moreover, every step is illegal and the cost of cracking is sky-high.

04. The ultimate "disguise""What can defeat human beings will eventually be human beings themselves"!

When human beings have the computer technology to go out of space civilization, can we clone a human and let this copied human crack all kinds of Captcha?

Of course, this is just a small series of lost fantasy, may be seen in science fiction films, fans do not take it seriously oh!

Well, that's all for today's content. Let's review it together with Xiaobian:

The "Turing test" is to tell who is a computer;

"Captcha" is to distinguish who is human;

Strange "Captcha" protect various computer systems;

"Computer technology" is constantly improving its ability to disguise itself as human.

As a "shield," how can Captcha be safer and easier to use?

As a spear, how can computer technology break through the strict defense of Captcha?

These questions need to be answered by smarter humans and smarter computer technology.

It can be predicted that Captcha, as a "battleground between humans and computers," will usher in more opportunities for attack and defense, and at the same time bring more changes to our society. Let's wait and see!

This article comes from Weixin Official Accounts: ZTE Document (ID: ztedoc), Author: ZTE Document

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.