Chapter 92: Sudden Situation [Subscribe for monthly tickets]

Although cryptography is simple binary, it contains complex changes and infinite possibilities.

It’s like a good game of hide and seek.

Others learn the most important hash function in cryptography, perhaps by working hard and persisting in research.

Xu Yuan, however, likes to think outside the box and look for new solutions.

The DM5 algorithm introduced by the Standards and Technology Bureau can be used to generate message summaries.

The principle is to first fill the length of the input information, load the standard magic number after storing the record, and finally go through four rounds of loop operations.

Because the DM5 algorithm contains many irreversible operations, a lot of original information will be lost and cannot be recovered.

There are many ways to break this algorithm, but one thing needs to be made clear.

The so-called cracking does not mean restoring the summary to the original text.

After all, the fixed 128-bit summary is finite, while the number of original texts is infinite.

Each summary can be obtained by using a hash function on several original texts.

Wang Xiaoyun and his team cracked the DM5 cryptographic algorithm using collision.

For example, if the original text A can generate summary B through the DM5 algorithm, then there is no need to restore X to A. It is only necessary to find the original text M and generate the same summary B to crack it.

To put it in a more vivid way, the MD5 results of A and M are the same.

But achieving a successful collision is extremely difficult.

After all, the Bureau of Standards and Technology has set up a special website for cracking the code, but no cryptography expert has yet managed to crack it.

Many scholars even choose to give up because it is too difficult and gradually turn to other research fields.

As a result, hash functions are the least active area in cryptography.

Only after Xu Yuan officially got on track in cracking the MD5 password did he truly feel the difficulty of it.

No wonder so many cryptography experts around the world choose to give up.

During the winter vacation when I was home, I used almost several notebooks of draft paper to solve equations.

But there has been almost no progress.

You should know that this is the result of Wang Xiaoyun's team gradually mastering the method after studying it for a period of time.

-

Task: MD5 password cracking
Subject: Cryptography
Progress: 10%
Result: Not completed
"There really hasn't been any progress these days. No wonder the Bureau of Standards and Technology is so confident."

Inside the room, Xu Yuan was watching the progress bar panel that was gradually disappearing from his sight after leaving the deep learning state, muttering to himself, he had never expected that cracking the password would be much more difficult than solving the Carmichael number interval problem.

However, his self-confidence was not affected by this. Instead, he felt that he became more courageous as the setbacks became more severe.

When you successfully crack it one day, you can imagine the sense of satisfaction that will surge in your heart.

Just as Xu Yuan was about to continue to deduce the equation, his sister Xu Ying's voice suddenly came from outside the door.

"Xiao Yuan."

"Going out to eat."

I reached out and picked up the phone on the table and pressed it, only realizing it was already noon.

"Come here."

He shouted something to the outside at the top of his voice, tidied up the drafts that covered the table, then stood up and walked out of the room.

Before, he was completely immersed in deep learning in order to keep himself at optimal efficiency.

So there is no feeling.

Now that my condition has recovered, I suddenly feel hungry.

In order to ensure that he could continue to be in good condition to solve the equation in the afternoon, he chose to fill his stomach first.

As the saying goes, the body is the capital of revolution. How can we crack the code if we don't ensure this first?

Since tomorrow is New Year's Eve, the meals at home these days are basically the same as the sumptuous New Year's Eve dinner. Almost every meal is filled with fish and meat, which Xu Yuan enjoys very much.

It is also worth mentioning that during the days when he returned to his hometown from the provincial capital, he did not forget to visit his third uncle's house in his spare time.

I helped my youngest cousin Xu Xiaolin with math lessons, which were all junior high school knowledge.

Although Xu Xiaolin is a girl, her mathematical ability is much better than her brother Xu Yahui. It didn't take her long to master the learning and problem-solving methods taught by Xu Yuan.

Xu Yuan was also quite pleased about this.

In addition, Xu Xiaolin's performance in other subjects is also relatively stable, so there will be no problem for her to be admitted to Guyuan No. 1 High School in two years.

Uncle San's family was naturally very excited to hear the news.

In addition to the fact that Guyuan No. 1 High School is very famous in the city, the key point is that Xu Yuan is from Guyuan.

Since Xu Yuan was able to make it out of Guyuan No. 1 High School, maybe his daughter would also have a chance to win the top spot and be admitted to Qinghua.

Xu Yuan was not interested in what his third uncle's family thought. Anyway, he had fulfilled his obligations as an older brother.

The next day.

New Year's Eve.

In the evening, the family sat around the TV as usual, watching the Spring Festival Gala.

It was almost twelve o'clock when I reluctantly returned to my room and took advantage of the day to get a few hours of sleep.

As for the subsequent procedures of setting off firecrackers, lighting incense, visiting graves and paying New Year's greetings, Xu Yuan was very familiar with them, and following his father's instructions, everything went smoothly and happily. The family spent the New Year safely and successfully, and welcomed a new life in the New Year.

When people started visiting relatives on the second day of the Chinese New Year, there was no doubt that Xu Yuan had become everyone's "someone else's child" again.

In addition to winning the top prize and the gold medal last time, he also proved the Carmichael number interval problem in number theory, published a paper in the Annals of Mathematics as a freshman, and participated in an academic conference that was reported by the Youth Daily. There are so many things he can talk about.

In this regard, Xu Yuan could only apologize to his cousins ​​silently in his heart again.

After the Chinese New Year until school starts again after the Lantern Festival, Xu Yuan doesn't need to do anything else.

So I can lock myself in the room again and continue to push the equations by hand to try to crack the MD5 algorithm, hoping to reach % progress as soon as possible.

Although Xu Ying and her parents didn't know what he was talking about, they would definitely not disturb him as long as he was studying.

However, as time passed, just as Xu Yuan was eagerly waiting for the cracking progress to improve, an unexpected situation occurred.

Almost as soon as he came up with the new equation, he suddenly caught a glimpse from the corner of his eye that the progress bar on the virtual panel had actually gone down.

-

Task: MD5 password cracking
Subject: Cryptography
Progress: 8%
Result: Not completed
"How could this happen?"

Xu Yuan looked at the progress bar on the panel and his face changed suddenly when he found that it had dropped by 2% compared to the previous few days.

Because he knew this matter very well.

As soon as he learned that he would see a special virtual panel progress bar when he entered the deep learning state, he conducted a detailed and thorough verification of the various uses of the panel progress bar.

If the progress bar suddenly drops, it means that you are on the wrong path.

But don't underestimate this 2%. If you don't find a way to make up for it, the mistake will only get bigger and bigger.

If you want to change it later, you will have to start all over again.

"I clearly derived the equation based on the progress of Professor Wang's team, so there shouldn't be a decline."

The sudden change made Xu Yuan lose the mood to continue calculating, so he stopped for a while and thought seriously.

First of all, he did not start from scratch to crack the MD5 password algorithm, and he is currently following the progress of Professor Wang Xiaoyun. He has enough confidence in deducing the equation.

So there is only one possibility left.

Wang Xiaoyun’s team’s current solution is problematic.

Did not grasp the correct direction.

If you continue to calculate in this way, you may eventually find an error and fail to crack the MD5 algorithm, but the time you spent will be wasted.

For scientific researchers who are racing against time, the impact this has is absolutely huge.

Think about it.

The best approach is to remind Wang Xiaoyun’s team.

Change your thinking and try again.

However, it is obviously not enough to give up the previous team's efforts just because of his words.

"It seems that I have to find time to go to Professor Wang, but before that I must find the correct direction to crack it."

The thought stayed here, and it didn't take Xu Yuan long to make a decision in his heart.

I want to determine the correct research direction for cracking MD5 passwords.

Although it seems very difficult to do this, with the data on the progress bar on the panel as a reference, it is not impossible to accomplish.

Just like this, Xu Yuan quickly immersed himself in the calculations again, and was so absorbed in it that the draft paper he had just written was thrown on the ground at random. If an outsider saw it, they would probably have the illusion that he was crazy.

The collision cracking methods of hash function passwords include brute force enumeration method, dictionary method, rainbow table method, etc.

The so-called brute force enumeration method, as the name suggests, is to simply and roughly enumerate all the original texts and calculate their hash values ​​to see which hash value is consistent with the given information summary.

Although this method is simple, it is extremely time-consuming and the desired results cannot be obtained by existing single-machine calculations.

This just proves that if the standard technical bureau releases it, it will not be cracked even if a supercomputer is used for a million years.

The dictionary rule is the opposite of the brute force enumeration method, which is to trade space for time.

But the consequence is that the storage cost is too high and the probability of use is relatively small.

Compared with these two methods, the most applicable method is the rainbow table method.

Through the attenuation function that converts the information summary into another string, through alternating operations several times, a chain of original text and hash value is formed. Each step of the operation is a different function, as beautiful as the colorful rainbow in the sky.

Wang Xiaoyun's team is currently using rainbow table collision cracking. Although it is a more balanced method compared to the other two, the results given by the progress bar on the panel show that it is not suitable for cracking the MD5 algorithm.

It is necessary to find a new collision method, and this is what Xu Yuan urgently needs to do.

The more a person is immersed in something, the faster time passes.

Because when you are really busy, you have no time to spare.

In a blink of an eye, almost half a month had passed. As the Lantern Festival approached, my sister Xu Ying had already returned to school, and my parents had gone to the provincial capital early to ask the tobacco and alcohol shop to open.

Only Xu Yuan was left at home, and he would go to Yanjing after the remaining two days of vacation.

Late that night, when Xuzhai Village was shrouded in darkness with only the occasional barking of dogs, Xu Yuan was still bent over the desk in his room, concentrating on calculating equations.

As more and more draft papers remained on the ground, Xu Yuan's expression became noticeably brighter.

……

(End of this chapter)