About Quantum security field

Recent trends in information security

Information and communications technology(ICT), such as the Internet, is the foundation for global development. Research and development of ICT is still ongoing, and social transformation is underway by using information and communications. On the other hand, cyberattacks are increasing as information and communication is utilized in society, and it is required that information security realizes safe and secure information and communication.

One type of information security technology is cryptography, which makes it impossible for a third party to decrypt the contents of a communication even if the third party eavesdrops on it. Most of modern cryptography is secured by the enormous amount of computation required for decryption, but there is a potential threat that ciphers will be easily decrypted in the future due to the emergence of new computing technologies such as quantum computers. There is also the possibility of an attack that eavesdrops on encrypted information for the time being and then decrypts the eavesdropped information when new computing technology is established.

Therefore, it is needed to switch modern cryptography to next generation of cryptography that cannot be decrypted in principle by any computer in the future. One such cryptography is “quantum cryptography”, which applies a technology called “quantum communication” to cryptography. Quantum cryptography is being researched and developed mainly in Japan, the United States, Europe, China, etc., and the construction of networks using quantum cryptography is being promoted. Quantum cryptography is expected to realize future in which important information handled in fields such as state secrets, medicine, finance, infrastructure, and manufacturing can be safely communicated.


Quantum communication


Quantum communication is a technology that applies quantum mechanics to communication. When transmit digital data in conventional communications, 0 and 1 are expressed using electricity or light as signals. However, in quantum communication, 0 and 1 are expressed as signals based on the state of the quantum of light itself (the smallest particle that cannot be further divided). Digital data can be shared between two parties when the sender generates a quantum signal and sends it to the other party, and the receiver measures the signal.

There are two main types of quantum communication. The first is a highly sensitive photodetector that allows the receiver to measure signals that have become weak during communication, enabling ultra-long distance, high-capacity communication. The second is a method in which a receiver measures a signal transmitted by a sender using a single quantum state as a signal, and a method for safely sharing digital data between two parties is devised by making use of the nature of quantum mechanics by setting the signal to the quantum level.

Quantum cryptography

Due to the nature of quantum communication, quantum cryptography is a technology that realizes cryptography that cannot be decrypted by any computer except the sender and the receiver.

Two technologies that make up quantum cryptography

Quantum cryptography consists of two technologies, quantum key distribution and one-time pad.


Quantum key distribution

Quantum Key Distribution (QKD) is technology to securely share cryptographic keys by quantum communication. A sender converts generated random number into a single quantum signal before sending it to a receiver. Once again, if the communication is eavesdropped, the quantum nature leaves some trace in the signal so that the receiver can reliably detect that it has been eavesdropped. Cryptographic keys can be shared without leaking them to third party by performing a process called key distillation for random numbers that are not eavesdropped.

One-time pad

One-time pad is a method of encryption by an encryption key which is discarded after it has been used. A sender sends information made by encrypting plaintext with an encryption key to a receiver, the receiver then computes the plaintext from the encrypted information and the encryption key. Even if a third party who does not know the encryption key eavesdrops on the communication, it will only look like random numbers. Since an encryption key changes with each communication, contents of plaintext will not be leaked unless the encryption key is leaked.

Quantum security field

Although quantum cryptography realizes the security of information and communication, quantum communication has limitations in performance such as communication speed and communication distance. In addition, some functions such as authentication and the tolerance to continuous eavesdropping are required because the function of quantum cryptography alone is insufficient as a security. Therefore, to solve the problems of information and communication, it is necessary to integrate peripheral technologies such as information theory, cryptography, and network technology with quantum cryptography.

At Quantum ICT Collaboration Center, we work to create a new fusion field called Quantum security field, which combines Quantum ICT field, such as quantum communication and quantum cryptography, with peripheral technologies.