"Come on, tell me what's going on?" Xie Han pushed the envelope in front of Zhang Chenyan. The envelope seemed quite thick, and the sender's identity was already indicated on the surface—Doctor.
Zhang Chenyan was puzzled. Why would the doctor send him a letter?
Most of his communication with the doctor was in the digital world, as it was much more convenient. Yet now, the doctor chose to send a letter, which could only mean he had something very important and urgent to notify Zhang Chenyan about, and since Zhang Chenyan couldn't enter the digital world at the moment, the doctor resorted to this method.
What could be so urgent? Zhang Chenyan couldn't figure it out.
"It seems there is something you're hiding from me after all," Xie Han said, putting down her chopsticks and looking at Zhang Chenyan. Though her tone wasn't interrogative, her demeanor still made Zhang Chenyan nervous.
"I'm not doing anything bad behind your back," Zhang Chenyan retorted, using a common tactic children employ to argue with their parents.
"Aren't you worried I already opened the envelope and read it?" Xie Han probed further.
Zhang Chenyan glanced at the envelope. The opening was on the back, so from this angle, he couldn't tell if it had been opened. But, maintaining his stance, he said confidently, "I trust you. You respect my privacy. Since it says 'To Zhang Chenyan' on the envelope, you wouldn't open my things."
This statement both conveyed his trust and subtly retaliated against Xie Han.
Xie Han, somewhat exasperated by Zhang Chenyan, feigned annoyance. "Fine, you win. Take the envelope and open it in your room. Don't forget to do the dishes tonight."
With that, Xie Han picked up her chopsticks and resumed eating.
Seeing this, Zhang Chenyan quickly grabbed the envelope and ran to his room, carefully closing the door behind him.
Holding the envelope, Zhang Chenyan felt something was off. It didn't feel like it contained paper; it was heavier and harder.
What is the doctor trying to say? Zhang Chenyan couldn't fathom it.
He hastily opened the envelope, only to find a piece of glass and a brief note inside.
After reading the note, Zhang Chenyan understood. The piece of glass in his hand was a new invention by the doctor, called a "new barrier." Though it looked like glass, it was much more advanced.
Not only could it maximally prevent temperature loss, but it was also extremely tough, acting like the barrier Zhang Chenyan had seen in the ground experience hall. Additionally, the doctor had used an old but practical technique: one-way visibility. Through this "new barrier," people could see outside, but creatures outside couldn't see in.
Realizing this, Zhang Chenyan understood the doctor's excitement. This development meant humanity had a better chance of returning to the surface, a highly beneficial prospect for the future.
Not only the creator of this material, but even Zhang Chenyan felt incredibly excited. If he could enter the digital world now, he would celebrate with the doctor.
Unfortunately, he had to stay home for the time being, so his joy could only be internal.
Yesterday, he had visited the surface experience hall, and today he learned about a possible return to the surface. The timing couldn't be more fitting. Perhaps before yesterday, Zhang Chenyan couldn't imagine life on the surface, but now, he had hope.
While contemplating how to celebrate with the doctor once he returned to the digital world, 0810 suddenly appeared in front of him.
Yes, without any warning, 0810 appeared.
As a high-level AI, she had no physical form in the physical world, existing only as a holographic projection.
This wasn't 0810's first appearance in the physical world, but it was Zhang Chenyan's first time seeing her holographic projection in such circumstances—a very pretty girl suddenly appearing in your bedroom while you're laughing manically at a piece of glass.
Fortunately, 0810 had business to attend to and wasted no time in teasing Zhang Chenyan.
"The current investigation results point to a problem with the hash algorithm."
True to her style, 0810 always delivered the most shocking news in the calmest manner.
Last time it was the duplicate IDs, and now it was the hash algorithm.
"A problem with the hash algorithm?" Zhang Chenyan immediately grasped the gravity of the situation but couldn't understand how the hash algorithm could have issues.
The hash algorithm was indispensable in the metaverse. People had long been accustomed to life in the metaverse, relying heavily on the stable operation of hash algorithms.
Simply put, a hash algorithm transforms an input of any length into a fixed-length output, known as the hash value. This conversion is a form of compression mapping, meaning the hash value space is much smaller than the input space. Different inputs may hash to the same output, making it impossible to determine the unique input from the hash value alone.
This was a feature of the hash algorithm.
"If we explain the hash algorithm as a function, it compresses any length of message into a fixed-length message digest," 0810 explained. "But you should also know, its significance in the metaverse lies in this function—identical inputs always yield the same output; different inputs yield different outputs with high probability."
"No problem there," Zhang Chenyan shrugged. "I've studied this. It's an essential course for anyone working in the digital world."
"Can you find its inverse pattern?" 0810 asked.
"Are you kidding?" Zhang Chenyan laughed. "A hash algorithm converts data into a signature tightly connected to every byte of the source data. Find an inverse pattern? By what method? Lifelong perseverance?"
0810 nodded. "Exactly. You can't, and I can't either because the hash algorithm is a critical means of verifying if the original data has been tampered with."
In fact, its role wasn't limited to this. It could enhance storage space utilization, improve data query efficiency, and provide digital signatures to ensure data transmission security.
Such an important algorithm, and now 0810 was telling Zhang Chenyan that it had an issue.
Taking a deep breath, Zhang Chenyan tried to process the news. Just after hearing a great piece of news, 0810 brought such bad news. What kind of luck balance was this, and could he unsubscribe from it?
But he knew this was no time for complaints.
After half a minute, he said to 0810, "Alright, go on. Is it the algorithm itself or how we're using it? How is this related to City R?"
Only 0810 could endure Zhang Chenyan's barrage of questions. She responded one by one: "The algorithm has been in use for years without such issues. Whether it's our usage causing the problem is still under investigation. This isn't just related to City R anymore; it might concern the entire metaverse."
Hearing this, Zhang Chenyan felt his heart sink.
If it involved the entire metaverse, it meant both the physical and digital worlds were affected.
He hadn't imagined the problem could spread so widely. If they had discovered it any later, the consequences would have been…
"What exactly is the problem?" Zhang Chenyan asked calmly.
"Hash collision," 0810 said seriously. "Someone has increased the probability of hash collisions."
"You're joking, right?" Zhang Chenyan blurted out.
A hash collision means two different inputs producing the same output.
Zhang Chenyan understood that hash collisions are inevitable because the output length is fixed while the input length is infinite, leading to inevitable collisions when mapping an infinite input set to a finite output set.
Collisions aren't the issue; it's the probability of collisions that matter. The security of a hash algorithm depends on this probability. A secure hash algorithm must ensure unpredictable outputs and low collision probability.
Unpredictable outputs mean any change in the input alters the output completely, making it hard to reverse-engineer the input from the output, except by brute force.
Of course, brute-forcing a hash is far more challenging than ancient alchemy; anyone with some intelligence wouldn't choose this method.
To reduce collision probability, researchers continuously seek superior hash functions and collision-handling methods.
Methods like linear probing, quadratic probing, and double hashing in open addressing, as well as chaining, are ways to handle collisions.
Countless related studies are conducted every year.
The metaverse wasn't built overnight.
It developed over time, encountering various problems that humanity continuously worked to solve.
"Are you saying someone intentionally increased the collision probability of an algorithm we've researched and used for years, and succeeded?" Zhang Chenyan almost laughed. He couldn't understand the motive behind such actions.
They had always strived to avoid this, researching countless handling methods, only to find someone sabotaging from the shadows.
"We don't understand their motive either," 0810 said, sounding helpless.
"Who benefits most from disrupting the entire metaverse?" Zhang Chenyan pondered.
"Are you implying the conservatives or us AIs?" 0810 was sensitive to this question.
"As an AI, or among the AIs you know, does anyone wish to oppose humanity?" Zhang Chenyan countered.
0810 looked down. "But don't humans love imagining such plots? Evil entities wanting to take over Earth and rule humanity."
Zhang Chenyan didn't know how to respond. After all, he had read many novels and watched numerous shows with such themes. Finally, he shifted the topic: "Increasing hash collision probability compromises security. I feel this might be related to the duplicate IDs, making our investigation harder and slower."
0810, however, seemed fixated on the previous question. She immediately responded, "If it's related to duplicate IDs, then it's unlikely to be AI-related since duplicate IDs only appear among humans."
"We don't know the victims and beneficiaries yet. Isn't it too early to conclude?" Zhang Chenyan looked at 0810.
In the end, 0810, adhering to scientific rigor, modified her statement: "Yes, it's all speculation now. It could be AI-related. After all, I and those around me don't represent all AIs."
Zhang Chenyan conceded, "True. Humans are also suspects. After all, humanity is diverse. A few crazies aren't surprising."
"Crazies?" 0810 asked. "Mad scientists?"
Zhang Chenyan thought for a moment before answering, "I prefer your term—'evil entities.' Essentially, some mentally unstable individuals."
"And crazies? How do you distinguish them?" 0810 asked another question.
"Obsession with something or unstable mental states?" Zhang Chenyan attempted to reply.
"Does that make you a crazy?" 0810 probed.
Zhang Chenyan shook his head firmly, "We undergo multiple psychological tests before employment and regularly after. I can assure you I'm mentally healthy."
0810 nodded, her purple eyes gazing directly at Zhang Chenyan as she said, "Then you might soon go crazy."