Quantum key distribution for a post-quantum world


The emergence of quantum computing and its ability to solve calculations at incredible speed by exploiting the fundamental properties of quantum mechanics could revolutionize our world. But what does this quantum future mean for data security?

As quantum computing scales from the test lab to the real world, this unprecedented new form of computing power has massive implications for current forms of encryption and public key cryptography (PKC), such as Rivest-Shamir- Aleman (RSA) and Elliptic Curve Cryptography (ECC). Faced with the processing capabilities of quantum computing, which can analyze large data sets orders of magnitude faster than current digital computers, these forms of encryption will become essentially vulnerable to bad actors.

In the coming post-quantum future, cryptography solutions based on the rules of quantum physics are essential to ensure that sensitive digital information is distributed securely over the future quantum internet. One of the pillars of this more secure quantum computing future is called quantum key distribution (QKD), which uses basic properties of physics to derive encryption keys for secure encryption between two locations simultaneously.

Harness the power of photons

At the physical level, the data bits sent during key exchanges for today’s common encryption techniques, such as RSA and ECC, are encoded using large photon pulses or voltage changes. With QKD, everything is encoded in a single photon, relying on quantum mechanical properties that enable detection and prevent successful eavesdropping. Quantum objects exist in a state of superposition where the value of a property of the object can be described as a set of probabilities for different values.

The transmission of coded photons occurs on what is called the quantum channel. A separate channel, called the classic channel, established between the two endpoints handles clock synchronization, key filtering or any other data exchange; this channel could be any conventional data communication channel.

Several varieties of QKD

A number of implementations and protocols for QKD are emerging as the technology evolves. For example, discrete variable QKD (DV-QKD) is used in many commercial QKD systems today. A DV-QKD system consists of two terminals: a transmitter and a receiver. The quantum connection between these endpoints could be free space or dark fiber. In this case, the transmitter encodes a bit value, 0 or 1, onto a single photon by controlling the phase or polarization of the photon. A separate data connection between the two endpoints is used to communicate information about quantum measurements and synchronization.

While initial QKD implementations consisted of separate dedicated fibers for quantum and data channels, newer versions can use separate wavelengths for each channel on the same fiber, allowing for more cost-effective deployments and efficiencies. .

Other implementations include the continuous variable QKD (CV-QKD) and entanglement. With CV-QKD, the sender applies a random source of data to modulate the position and momentum quantum states of the transmission. QKD entanglement, on the other hand, exploits quantum phenomena where two quantum particles are generated in such a way as to share quantum properties; no matter how far apart they are later, a measurement of a property on each will result in the same values.

Upcoming challenges for QKD

Distance remains a constraint when implementing QKD over fiber because individual transmitted photons will be absorbed over distance. The laser force is attenuated to create the individual photons, and standard telecommunications equipment cannot be used to repeat or reinforce the signal. In general, between 60 miles and 90 miles is the practical limit.

Methods to extend the distance include secure exchange, dual-field QKD, and quantum repeaters.

  • Trusted exchanges act like a repeater – receiving optical signals, converting them to digital, then converting them back to optical. Trusted exchanges must be secure to prevent an intruder from reading the transmission while it is in digital form.
  • The dual QKD field adds a mid node that receives signals from both terminal nodes, increasing the distance between the terminals to potentially hundreds of kilometers.
  • Quantum repeaters could eventually break down the distance barriers of QKD over fiber, providing a similar function to repeaters in today’s telecommunications: to amplify or regenerate data signals so they can be transferred from terminal to terminal. another.

Advances in single photon sources and low noise detectors will further improve viable distances for QKD.

What’s next for QKD

QKD has significant value in a quantum world due to its ability to enable symmetric key sharing between endpoints and identify when eavesdropping on the quantum channel occurs. However, before it can be widely implemented by carriers, QKD must be supported in a carrier environment, delivering the availability and reliability that their customers expect.

For example, disruption of the quantum channel can lead to the loss of key material in real time; however, having secure key storage associated with QKD allows key material to continue to be distributed during the investigation of the Quantum Channel unavailability. It also means that approaches and capabilities for troubleshooting and managing QKD equipment and services need to be developed.

Since QKD is based on quantum mechanics, the observation state will have an impact on the quantum system, which in itself poses problems for troubleshooting and management. As technology continues to evolve and improve, QKD implementations on smaller mobile devices such as drones may eventually become possible. Regardless of how QKD evolves, it seems to be a promising solution for securing communications over the quantum internet.


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