Along with AI, quantum technology is one of the hot topics in the tech world. With the big difference that the first one is now ready for use. What about quantum computers?

If the prophecies of doom are to be believed, quantum computing will make any current form of encryption as useful as a trailer hitch on an airplane. Are these messages correct? Should we start fearing quantum capabilities yet? We let Kristof Verslype, cryptographer at Smals, speak.

Suggest a little

Quantum technology works with qubits. These are subatomic particles that only have a fixed value when we actually measure them.

Verslype begins with something that is almost a mantra for many: quantum computers will solve all problems that are too difficult or even impossible for classical computers. “People sometimes tend to attribute mythical properties to a technology they do not understand,” he explains. “The same applies to quantum computers.”

People sometimes tend to attribute mythical properties to a technology they do not understand.

Kristof Verslype

“Then the question arises: What is actually the theoretical performance of quantum computers?” Verslype goes further. That depends on the problem. He divides it into four categories:

• No added value
• Probably no added value
• Possible added value
• Clear added value

“Sufficiently powerful quantum computers can have added value,” emphasizes Verslype. A good example is simulations of natural processes. “And we are confident that sufficiently powerful computers will be able to crack large parts of our modern cryptography.” The important words have already been said.

Global

“Despite or perhaps because of this uncertainty, you can see that a lot of resources around the world are flowing into quantum technology. The estimate for this year is $36 billion,” says Verslype.

He distinguishes between two types of quantum technology:

• computer
• communication

“Quantum communication or quantum Key exchange “It’s not the most practical solution, but it’s a way to protect us from the threat of powerful quantum computers when it comes to data in transit.” Verslype continues.

Current condition

For the more practical side of things, Verslype uses a message as an example. The headline says Google has achieved “quantum supremacy.” What exactly does that mean? “Less than you would intuitively think,” he explains. “This means that a quantum computer can solve a problem that a classical computer cannot solve.”

Days later, IBM denied the claim. There was a similar breakthrough in China, but just like Google, with a problem tailored to quantum technology. So not directly representative of reality.

The currently most powerful quantum computer is the 2022 IBM Osprey (433 qubits). “What can we expect in the coming years?” Verslype asks the question itself. The IBM Condor with 1,121 qubits is on the way. This is the first quantum computer with more than a thousand qubits. According to Veslype, a great achievement.

“What’s also interesting is that they are aiming for exponential growth,” he continues. “This means that the number of qubits doubles every few months. However, the number of qubits does not say everything. They contain noise and the more noise, the less precise the qubits are and the less powerful the quantum computer is.”

The more noise, the less precise qubits are.

Kristof Verslype

Building a quantum computer faces three major challenges:

• insulation for a long coherence time – the quantum state is sensitive to external stimuli and remains coherent during this time
• Error correction – applied to the concept that a group of qubits forms a logical qubit
• Scalability – exponential qubit growth over sufficient time and with high accuracy

“If quantum computers are ever to pose a threat to modern cryptography, we need not a few hundred, but tens of millions of qubits,” says Verslype.

Two main types

The word “cryptography” was mentioned a second time. “In the past, cryptography was used to protect data at rest,” says Verslype. “But today we see that cryptography is much more. There is the category Public key, for example with authentication. There is also symmetric cryptography, whose largest block consists of symmetric encryption.”

“Symmetric encryption means that encryption and decryption occur with the same key. The global standard is AES,” he continues. “Breaking encryption usually means that an attack succeeds in discovering the decryption key. bee Public key-Encryption Anyone can encrypt with the public key, but only the owner of the private key can perform decryption.”

Symmetrical

Verslype explains the influence of powerful quantum computers on symmetric encryption using a fictional example.

• Data encryption with a length of 6 bits – 64 possible keys
• The average attacker needs 32 attempts
• With a quantum computer, the possible number of keys is reduced to 8
• The average attacker then only needs 4 attempts
• Increase encryption to 12 bits
• Potential key count for quantum computers increases to 64

“In reality we use at least 128 bits. By doubling it to 256 bits, the risk is almost completely contained.” Verslype reassures us.

The number of logical qubits required for 256-bit encryption is 6681. That’s at least ten million physical qubits.

audience

After Public key-Encryption. “Most systems are currently based on RSA or Elliptic Curve encryption,” says Verslype. “RSA is about prime numbers.”

An RSA assumption is that the product of an operation with two sufficiently large prime numbers cannot be decomposed by an algorithm. To break an RSA of 2048 bits requires approximately 4,096 logical or twenty million physical qubits.

Breaking a p256 elliptic curve (a NIST standard) requires 1536 logical or thirteen million physical qubits. These are numbers that we have not yet arrived at. To pose a real threat to modern cryptography, not only are many more qubits needed, but they also need to be much more precise.

collect data

Verslype: “Modern Public keyCryptography involves mechanisms based on assumptions that no longer apply to powerful quantum computers. We need to develop new cryptographic mechanisms that are also important for powerful quantum computers.”

For him it is clear: “Suppose there is an attacker today who collects a lot of encrypted data.” It can store this data for years until access to a sufficiently powerful quantum computer is available. At this point our attacker can decrypt this data. This scenario makes us think long in advance.”

This is why NIST started standardization. Four algorithms were selected to become the standard next year, as well as eight alternatives. The KUL has already broken one of these eight. In addition, since 2022 there has been a call to find better digital signature solutions. It is also important to know that the implementation of algorithms can sometimes be vulnerable.

Diploma

In all likelihood, a real threat from quantum computing is still a long way from current cryptography. Verslype even cites a report from 2021 in which the American NSA does not dare to say whether and when a sufficiently powerful quantum computer will ever be created. A year later, the agency advised that it was best to prepare now.

Finally, Verslype also provides what the Federal Office for Information Technology BSI says about quantum computers. This organization recommends that post-quantum cryptography should not be used in isolation, but only in hybrid mode. However, he was assured that they would abandon this within a few years.

Added to this is cryptographic flexibility, which prepares existing mechanisms for the future in the best possible way. “I notice that this is rarely really defined, I would like to make it a little more concrete,” says Verslype. So he wants to see this on three levels:

• Organizations – clear guidelines for cryptography
• Interwoven across projects
• Programming – modular coding is always good

So we still have a long way to go, but there’s nothing wrong with thorough preparation.