China’s Micius satellite, launched in 2016, was celebrated around the world as the first of its kind — a quantum communication satellite. It was built to send secret messages between Earth and space using the laws of quantum physics.
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The goal was to create an unhackable system, one that couldn’t be broken even by the most powerful computers.
This was done using a technology called Quantum Key Distribution (QKD). This method uses tiny particles of light, called photons, to carry information. These photons are sent from the Micius satellite to a ground station on Earth. The magic of quantum physics means that if anyone tries to spy on these particles, the message changes, and the tampering is revealed immediately.
To make things even more secure, Micius used a special trick called the decoy state protocol. This means it mixes real messages with fake ones. The fake ones act as traps — if someone tries to intercept them, the system knows something’s wrong.
But now, new information shows that Micius and its security system might not be as perfect as it seemed.
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Timing Errors Give Away the Secret
Between 2021 and 2022, scientists studying data from Micius found something unusual. They noticed that the laser pulses, which carry the photons, weren’t firing exactly when they were supposed to. These laser signals were sometimes slightly off — by just 100 to 300 picoseconds. That’s only a tiny fraction of a second, but in quantum communication, even such a small delay can be dangerous.
The problem is that these tiny timing errors could allow someone with very sensitive equipment to tell the difference between a real signal and a fake one. That’s not supposed to be possible. The strength of the system depends on the idea that attackers can’t tell which photons are real and which are just decoys.
If an attacker figures out which are the real photons, they can start collecting information about the actual encryption key. This kind of trick is called a side-channel attack. It doesn’t attack the encryption directly. Instead, it uses clues from the way the system behaves — like small timing differences — to find a way in.
To help understand this better, think of it like a combination lock. The lock is perfect, but someone might be able to hear small clicks when you turn the dial. By listening closely, they could guess the code. That’s what the attacker might do with Micius — listen to the “clicks” caused by the timing delays in the laser pulses.
Tests showed that using those timing clues, a well-equipped attacker could tell the difference between real and fake signals 98.7 percent of the time. That’s a huge problem for something that’s supposed to be secure.
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Fixes Suggested, But the Flaw Remains
The flaw lies not in the theory of quantum communication, but in the way it was built and operated in real life. Quantum encryption is still sound — the problem comes from how the Micius satellite handled its laser pulses.
The reason for the flaw may be due to small differences in how each of the lasers on the satellite fires. If multiple lasers are used, and they don’t fire at exactly the same time, delays can happen. Those delays were enough to break the secrecy that was supposed to be guaranteed.
Several solutions have been suggested to fix this issue. One idea is to use just one laser instead of several, which could remove the chance of these small timing mismatches. Another fix might be to better synchronize the lasers, making sure they all fire at exactly the right moment.
More careful pre-launch testing could also catch these problems before satellites are sent into space. Scientists also believe that satellites like Micius should be built with systems that allow fine-tuning from Earth. That way, if something goes wrong, ground controllers can adjust the lasers’ timing, temperature, current, or other key settings.
While the flaw doesn’t mean quantum communication is useless, it does show how important it is to pay attention to every tiny detail in space technology. Even the smallest errors — ones that happen in trillionths of a second — can open the door for someone to slip in unnoticed.
This discovery highlights how real-world devices, even ones based on groundbreaking theories, can still face serious risks. It’s a reminder that space security isn’t just about big ideas — it’s about making sure every piece of equipment works perfectly, down to the tiniest part.
