Quantum cryptography is the exploiting of quantum-mechanical properties such as quantum entanglement, measurement disturbance, no-cloning theorem, and the principle of superposition to perform encryption tasks. Quantum encryption plays a crucial role in the secure processing, storage, and transmission of information. One aspect of quantum cryptography is quantum key distribution (QKD), which offers an information-theoretically secure solution to the key-exchange problem. Quantum cryptography allows the completion of cryptographic tasks that are proven or conjectured to be impossible using only classical (i.e., non-quantum) communication. Furthermore, quantum cryptography affords the authentication of messages, which allows the legitimate parties to prove that the messages were not wiretapped during transmission. Thus, in a cryptographic set-up, it is impossible to copy, with perfect fidelity, the data encrypted in a quantum state. If one attempts to read the encrypted data, the quantum state will be changed due to wave function collapse (no-cloning theorem). This could be used to detect eavesdropping in QKD schemes, or in quantum communication links and networks. These advantages make quantum cryptography important in the digital age, where devices are increasingly interconnected and cyberattacks have become increasingly sophisticated. Quantum-mechanical properties – more specifically, quantum authentication – are critical components in the advancement of a quantum internet, as they establish robust mechanisms to ensure the long-term privacy and integrity of digital communications and systems.
History
In the early 1970s, Stephen Wiesner, then at Columbia University in New York, introduced the concept of quantum conjugate coding. His seminal paper titled "Conjugate Coding" was rejected by the IEEE Information Theory Society but was eventually published in 1983 in SIGACT News. In this paper he showed how to store or transmit two messages by encoding them in two "conjugate observables", such as linear and circular polarization of photons, so that either, but not both, properties may be received and decoded. It was not until Charles H. Bennett, of the IBM's Thomas J. Watson Research Center, and Gilles Brassard met in 1979 at the 20th IEEE Symposium on the Foundations of Computer Science, held in Puerto Rico, that they discovered how to incorporate Wiesner's findings. "The main breakthrough came when we realized that photons were never meant to store information, but rather to transmit it." In 1984, building upon this work, Bennett and Brassard proposed a method for secure communication, which is now called BB84, the first Quantum Key Distribution system. Independently, in 1991 Artur Ekert proposed to use Bell's inequalities to achieve secure key distribution. Ekert's protocol for the key distribution, as it was subsequently shown by Dominic Mayers and Andrew Yao, offers device-independent quantum key distribution. Companies that manufacture quantum cryptography systems include MagiQ Technologies, Inc. (Boston), ID Quantique (Geneva), QuintessenceLabs (Canberra, Australia), Toshiba (Tokyo), QNu Labs (India) and SeQureNet (Paris).
Advantages Cryptography is the strongest link in the chain of data security. However, interested parties cannot assume that cryptographic keys will remain secure indefinitely. Quantum cryptography has the potential to encrypt data for longer periods than classical cryptography. Using classical cryptography, scientists cannot guarantee encryption beyond approximately 30 years, but some stakeholders could use longer periods of protection. Take, for example, the healthcare industry. As of 2017, 85.9% of office-based physicians are using electronic medical record systems to store and transmit patient data. Under the Health Insurance Portability and Accountability Act, medical records must be kept secret. Quantum key distribution can protect electronic records for periods of up to 100 years. Also, quantum cryptography has useful applications for governments and militaries as, historically, governments have kept military data secret for periods of over 60 years. There also has been proof that quantum key distribution can travel through a noisy channel over a long distance and be secure. It can be reduced from a noisy quantum scheme to a classical noiseless scheme. This can be solved with classical probability theory. This process of having consistent protection over a noisy channel can be possible through the implementation of quantum repeaters. Quantum repeaters have the ability to resolve quantum communication errors in an efficient way. Quantum repeaters, which are quantum computers, can be stationed as segments over the noisy channel to ensure the security of communication. Quantum repeaters do this by purifying the segments of the channel before connecting them creating a secure line of communication. Sub-par quantum repeaters can provide an efficient amount of security through the noisy channel over a long distance.
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