How high-speed quantum encryption could help secure the future internet

By Jean-Jacques DeLisle, contributing writer

Quantum computing promises computational speeds at a threshold previously unimagined. There are many practical benefits to having accessible quantum computing technologies in this world of big data and new data-driven scientific discovery. However, the current generation of security codes and cryptography relies on the principle that computers with modern capabilities would take too much processing time to be a threat. This isn’t the case with upcoming quantum computers, and a new regime of cryptographic technologies are required to provide security for banking, health care, governmental, and military systems.

According to Daniel Gauthier, professor of physics at Ohio State University, we are now likely to have a functioning quantum computer that might be able to start breaking the existing cryptographic codes in the near future. “We really need to be thinking hard now about different techniques that we could use for trying to secure the internet,” said Gauthier.

Researchers from several U.S. universities and a university in Singapore have striven to develop a commercially viable method of thwarting the security problem that quantum computers pose. Their solution is to use other quantum phenomenon to provide provably secure and high-rate quantum key distribution. Unlike many far-reaching research projects, these researchers constructed their system with commercial off-the-shelf components and leveraged a protocol that could also be used with free-space quantum channels, not just fiber-optic and infrastructure-based quantum channels.

A new technique can transmit quantum encryption codes quickly and safely. Image source: Pixabay.

One of the main issues that the group sought to find a solution for was the low key generation rates of earlier quantum key distribution systems, which are several orders of magnitude slower than conventional key distribution systems. With such a low key generation rate, the early systems were unsuitable for use with many high-data-rate communications processes. Other prior work features quantum key distribution systems based on superconducting nanowire single-photon detectors and qubits (quantum bits), which improved, but still limit, the key generation rates.

“At these rates, quantum-secure-encryption systems cannot support some basic daily tasks, such as hosting an encrypted telephone call or video streaming,” said Nurul Tamir Islam, a graduate student in physics at Duke University.

This latest research proposed the use of high-dimensional (d>2) quantum states, or “qudits,” to provide greater robustness and improved efficiency compared to earlier quantum key distribution systems. Qudits pose an interesting promise because the number of bits that can be encoded on a qudit is unbounded, scaling logarithmically with d. Qudits can also be used to increase the key generation rate in systems limited by the saturation of single-photon detectors, and qudits feature greater resistance to quantum channel noise, which allows for lower bit-error rates compared to qubit-based systems.

“It was changing these additional properties of the photon that allowed us to almost double the secure key rate that we were able to obtain if we hadn't done that,” said Gauthier, who began the work as a professor of physics at Duke University before moving to Oregon State University.

The security for this new quantum key distribution system is based on entropic uncertainty relations for qudits, a recently developed technique. This new process enables finite-key bounds for mutually unbiased states and is thus secure versus coherent attacks. A three-intensity decoy-state method is used to estimate the single-photon statistics and extract the secret key, and a bound for an extractable secret key length is determined by measured data.

“We wanted to identify every experimental flaw in the system and include these flaws in the theory so that we could ensure our system is secure and there is no potential side-channel attack,” said Islam. “All of this equipment, apart from the single-photon detectors, exists in the telecommunications industry, and with some engineering, we could probably fit the entire transmitter and receiver in a box as big as a computer CPU.”

Given the threat of quantum computing to conventional cryptography and security technologies, greater research efforts are necessary to realize commercially viable systems for protecting critical information. If these encryption systems can be made available prior to the advent of accessible quantum computing, we may avoid a time when even the most secure conventional encryption technologies could easily be hacked.