Han Jingchen said nothing, frowned, and flipped through a code book that had been torn in half. The book contained groups of six digits, with 20 groups in four columns and five rows on each page.

191422 013918 243176 334358 098675 234480……

Song Qiubai said, "Although we have obtained the code book, their encryption method has not been examined. Now our task is to crack the encryption method."

Zhou Bangguo was a tough nut to crack. He refused to tell us the encryption method no matter what. Time was running out, so we had to interrogate him and crack the code at the same time.

"Their encryption method is neither the traditional modulo-26 addition nor the XOR operation. The order of the codebooks and the starting position of the ciphertext are unknown... So, we have to try every possible method next."

This is what brute force cracking means, but you can't try each one, which is very time-consuming.

Han Jingchen tapped the table with his index finger and looked at the password book thoughtfully, "Has Cheng Hao been to Shanghai Publishing House before?"

The comrade in charge of investigating Yuan Weicheng was stunned by the question, then came to his senses and said, "I went there once in May last year, and now in Shanghai and Shanghai, we are secretly investigating all the people who came into contact with him during that period."

Han Jingchen nodded and looked at the person who was examining Zhou Bangguo. "You said before that Zhou Bangguo often went to the Xinhua Bookstore in the west of the city?"

"I asked the neighbors nearby, who said that he had a bad leg and rarely went out. He was a loner. He went to the nearby Xinhua Bookstore to read every month. The staff at the bookstore also confirmed that although he came to the bookstore several times a month, his time was not very regular."

"Every month?"

"Yes, every month."

Song Qiubai immediately looked at Han Jingchen, "Old Han, what did you find?"

Everyone present also looked at 놛: "Yes, Han, is there an accomplice in this Xinhua Bookstore?"

How come all these people are infiltrating the bookstore? Is it some kind of important organization? Or are the people in the bookstore being controlled?

Han Jing was silent for a moment, then suddenly put the password book on the table and stood up. "Let's go to Xinhua Bookstore first. If I'm not mistaken, this password book should only be half of the key. The other half is still in Xinhua Bookstore."

"Ah? Half?"

…

With the clue, everyone immediately got busy.

The censors were responsible for continuing to interrogate Zhou Bangguo and Yuan Weicheng, especially Zhou Bangguo, Han Jingchen and Song Qiubai, who went to Xinhua Bookstore in person.

"That Comrade Zhou?" The staff in the bookstore had a deep impression of Zhou Guobang. "He often reads books at this position."

Song Qiubai glanced through several nearby bookshelves, all of which contained books on literature, philosophy, art, and humanities magazines.

놛 asked, "What kind of books do you read when you are busy?"

"This..." The worker recalled seriously, "Sorry, there were too many people in the bookstore, and I didn't pay attention to what I was reading."

Han Jingchen looked around carefully and walked to a bookshelf full of periodicals. "These magazines will be published every month?"

"Not every month. For example, these are published every two months, these are published every month, and there are a few that are published twice a month. These will be published at the beginning of each month, these will be published in the middle of the month, and there are also those that are published at the end of the month..."

The workers understood the situation very well and explained it in detail.

Han Jingchen nodded and took down several books that were published before the 5th of each month.

It is certain that between the Zhou Bangguos, when they did not communicate every month, there must be a random and unique codeword known to each other.

Han Jingchen looked at the journal code. Since the implementation of the national unified book numbering system two years ago, all books have their own unique codes, which are composed of a series of numbers including the classification number, publisher code and serial number.

Song Qiubai looked at the look on his face and then at the periodicals. He realized something and said to the staff, "Let's buy all these books."

…

The cold wind was mixed with fine ice and snow, howling and whistling. This winter was unexpectedly colder than previous years.

On the way back to the base, Han Jingchen and Song Qiubai were both thinking about the complete key.

In the past, Song Qiubai had been obsessed with deciphering the secrets, forgetting to eat and sleep, and could not extricate himself from it, but today he was somewhat absent-minded.

"Old Han, I think you should come back to our intelligence team." Song Qiubai said to Han Jingchen while sitting in the co-pilot seat.

놛 really wants Han Jingchen to come back.

Han Jingchen drove the car, his eyes fixed on the front, his expression did not change, "There is no need to go back, I am very satisfied with the current troops."

Song Qiubai: "But it's a pity that you are not working in the intelligence organization."

I also feel sorry for losing such a partner and competitor.

At first, Dong and Han Jingchen entered the intelligence unit training in the same year. They both studied telegraphy and cryptography, as well as reconnaissance and espionage techniques.

However, 놛 is better at math and logic to crack various codes, while Han Jingchen is better at detection and analysis.

놛I am fascinated by the world of cryptography, encryption, decryption, encryption upgrade, and decryption again... Every decryption mission is an invisible bloody massacre, a game of wisdom, and a comparison of mathematics and logic.

I originally thought that they were the most tacit partner and the biggest competitor, but I didn't expect that... a year later, Han Jingchen was transferred to another place.

"There's nothing to regret. For me, I have no interest in dealing with these boring numbers all day long." Han Jingchen didn't think it was a pity. If he had to choose again, he would still choose the current camp.

"…" Dull, boring?

Song Qiubai was about to say more words of persuasion, but they were suddenly stuck in his throat.

…

After receiving the journals and codes, everyone began to analyze them using the microcode book.

Han Jingchen said: "We will send a secret message on the morning of the 5th of every month. Now it is the 5th, and we still have 3 days."

"Team Korea, we don't have the secret code yet, how are we going to decipher it?" In a formal setting, Jiang Ye did not call Chen Brother.

Jiang Ye had worked as a reconnaissance soldier for a year and knew a little about telegraphy.

The one-time pad encryption method does not require a cipher machine, but only a set of pocket password books, which can be a phone, a tape, or a book.

Both parties in the communication must have a notebook that can be torn page by page, with several columns of letters or numbers printed randomly on each page. To ensure safety, the entire page of the notebook must be torn off and destroyed immediately after use.

This means that although we have previously intercepted ciphertexts, the previous keys have long been torn up and become eternal secrets, and it is impossible to analyze the encryption method from the corresponding ciphertexts and codebooks.

Han Jingchen looked calm as he looked at everyone: "If each message is encrypted with a unique key, we will need to mass-produce the keys. For every million encrypted messages, we will need a million different keys, and we must also send these keys securely to the other party. What do you think they will do?"

If there is a way to get the key to the other party safely, why not just get the message to the other party directly?

"So, I suspect that the real codebook is not the miniature codebook in the basement, but these publicly distributed journals."

This means there is no need to produce it yourself, the quantity is sufficient, the content is guaranteed to be unique, and the other party is guaranteed to receive it.

Jiang Ye's eyes lit up. Yes! Why didn't I think of that?

Doing so not only reduces production costs, but also solves the problem of key transmission.

Then, Jiang Ye started to bite and gnash again, "These people are so cunning!"

Using publicly released journals can solve the trouble of producing and transmitting keys, and using micro code books to encrypt again to ensure foolproofness. Once the books and ciphertexts are leaked, their micro code books and encryption methods must be obtained to decipher their intelligence.

For example, 210723 means the 23rd word on the 7th row on page 20 of a book. The first word on the one-time password book is a random number 191422, which is encrypted into 402145 in a pre-agreed way. The party who receives the ciphertext also has the same password book, which is used to decrypt the plain text 210723. The party then searches for the corresponding word in the pre-agreed book, and then tears off this page or this number string in the password book.

By analogy, the 괗th character can be encrypted with the 괗th random number on the 괗th page, or it can be encrypted with the 괗th character on the first page.

With a breakthrough, everyone was full of energy and wanted to work all night to uncover the secret.

…

When Pei Manning woke up, it was already the afternoon of the next day.

Her eyelashes trembled, and then she slowly opened her eyelids. The world in front of her was a little blurry and chaotic.

"Hey, comrade, are you awake? How are you feeling?" The nurse who was giving her an IV was the first to notice that she had woken up.

Pei Manning's face was still pale, and her eyes were dazed for a while before they gradually focused and she looked at the nurse next to her.

"Where is this?" she asked in a still weak voice.

"Hospital, you were in a coma before, don't you remember? Oh, yes, it was Comrade Han and Comrade Jiang who brought you here."

Pei Manning's eyes flickered slightly, and he frowned and asked, "What's wrong with me?"

The nurse continued, "Doctor Yang has examined you, but has not yet found the cause of the disease. However, you don't have to worry. As long as you don't get too emotional, there will generally be no problem."

Pei Manning nodded lightly and breathed a sigh of relief in her heart. It seemed that the inspection methods here could not detect anything.