Wet air, icy concrete roads.

The yellow flowers at the school gate bloomed in unison, but there was no fragrance, but there was an astringent feeling.

The teaching building of Zuolu No. 1 University is surrounded by a strange atmosphere.

A piece of A4 paper, covered with dirt, was stuck in the center of the bulletin board.

And it was this piece of paper that attracted countless students to come and watch.

On the top of that piece of paper, a large, eye-catching skull was printed. This pattern really attracts the attention and curiosity of students who don't usually care about the bulletin board.

Just looking at the skull, I don't see what it means. The students could only keep looking.

Underneath the pattern, there are two groups of letters listed as if there is some pattern.

examp

lbcdf

ghijk

norst

uvwyz

――――――

keywo

rdabc

fghij

lmnps

tuvxz

And directly below these two sets of letters, a string of letters that look even more weird is given.

【rj/mr/om/de/gn/dr/xr/et/rm/ev/fo/ur/oo/al/td/fk/ly】

"Hey! What to do! Scatter, scatter, scatter! ”

Finally, a teacher appeared nearby to maintain order. And mixed with the student crowd, several teachers standing in front of the bulletin board also frowned.

I habitually bit the tip of my right thumb, biting on the outside of my fingernail and the inside of my thumb, biting hard, and the piece of flesh that I was bitten turned red and white.

Since I don't have any memory of before I came to this school, I can't be sure if this habit has been maintained from before until now.

"Now, Su Chen, what does this mean?"

The girl next to me asked in a whisper as she looked at me thinking about something seriously.

"Whose prank? Or did the microcomputer teacher's report slip stick up? ”

“t…… t、h…… t、h、e……”

I muttered to myself.

"Huh?"

She tilted her head in confusion.

"My pen is out of water, Luo Ling, can you lend me a pen, I want to write it down."

Hearing my words, she nodded, reached into her school bag, pulled out a doll pencil case embroidered with a large crocodile head, and took out a pink pen.

I held the black umbrella in my left hand, and with my right hand, I took out the small black book I carried with me from the built-in pocket of my clothes.

The kitten on the left shoulder purred in dissatisfaction because it felt the vibration and was disturbed to sleep.

After memorizing the odd monograms, the girl and I struggled to squeeze through the crowd and walked slowly to the classroom of the fifth class of high school.

"That, Su Chen, can you read those letters?"

Luo Ling suddenly tugged at the corner of my coat and asked tentatively.

"It's not so much that I can read it, but that I know how to understand it."

As I spoke, I couldn't help but sigh.

I really can't think of a guy who would do such a thing, or any reason to do it.

"Roar? Can you understand it too? It's amazing! ”

Behind me came a calm and calm male voice.

"Woo~~Ahh

The sound came so suddenly that I let out a small scream of shame.

I jerked around, and at some point standing behind me was the number two person in the Occult Research Society, and the first-class danger designated by the Student Council and the Political and Educational Office—Mickey in a white coat with messy hair.

"It's you...... Don't be scary, okay......"

I stroked my chest and said as I breathed.

"Hehehehe, I'm just talking in a normal way. But it's normal for you to be scared, because I've hidden my breath! Roar hahahahaha!! ”

As she spoke, Mickey let out an exaggerated laugh.

The weirdest thing is that no one is even laughing at the people passing by, they are all respectful and distant.

"Uh...... Su Chen, Mickey, what the hell is on that list......"

Luo Ling's pale blue eyes were full of curiosity, and she asked a little impatiently.

"Well, I think it's a two-party password."

Mickey pushed his glasses and replied with a smile.

"Ear... House...... Password? ”

Luo Ling asked suspiciously.

I took a deep breath and began to explain the auricula to her...... No, it's a two-party password.

"The so-called two-party password is encrypted with two 5×5 matrices. Each matrix has 25 letters and is a cryptographic method. ”

"Whoa! That's right! ”

Mitch continued with me.

"And it's still very simple. First, find the position of the first letter in the upper matrix, then find the position of the second letter in the lower matrix, and find the first letter in the upper matrix, and the second letter in the same column; In the matrix below, find the first letter in the same column, and the second letter as the same letter, and those two letters are the result of encryption. ”

Listening to the words of the two of us, Luo Ling also blinked thoughtfully.

"Sounds simple, but isn't the encryption method the same as the decryption method?"

"That's right, so it's too simple to say that the encryption method of the two-party password."

I replied.

And then she tilted her head again, as if she was thinking about something.

"In that case...... If two words are in the same column...... Isn't the content exposed? ”

She's thinking really fast!

I looked at the little book in my hand and nodded.

"Yes, this is one of the weaknesses of the two-party password, for example, with the matrix just now, if the yw is encrypted, then the encrypted/processed cipher is still yw. In this case, about 20% of the encrypted content will be exposed."

As soon as I finished speaking, her eyes brightened instantly.

"Good...... It seems to be really funny! Hey, let's crack the ciphertext now!! ”

After that, Luo Ling jumped and 'broke in' into the fifth class of the second year of high school.

I always feel ......

"Seems to have aroused her interest......

I said to Mitch.

……

However, I was silent.

I turned my head and the Mickey guy disappeared from behind me at some point......

……

"RJ/MR/OM/DE/GN/DR/XR/ET/RM/EV/FO/UR/OO/AL/TD/FK/LY, I should have copied correctly."

After deciphering the ciphertext, I bit the tips of my fingers again and tightened my eyebrows.

Sitting in the last room by the window, I cocked my stool and swayed back and forth, still thinking about the plaintext of the two-party password.

The kitten on my shoulder almost fell to the ground a few times, but it finally changed its mind, jumped on my legs, curled up comfortably, and continued to rest.

"Luo Ling, what did you solve over there?"

I turned my head to look at Luo Ling, who was sitting across the seat from me, and she also seemed to have doubts about the plaintext I had deciphered.

"Hmm...... Let me read it...... th/eb/om/bw/il/lb/ed/et/on/at/ed/at/fo/ur/te/en/oc/lo/ck…… That's it. ”

It looks like the decipherment is correct.

the/bomb/will/be/detonated/at/fourteen/o'clock

Translated, the bomb will be detonated at fourteen o'clock.