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Code and Cryptography

Error-correcting code and Cryptography are the fundamental technologies to realize secure and reliable information systems. We are working on both theory and practical aspects of code and cryptography. The results of our research have been contributing to a wide variety of NEC's products and services.

Cryptographic Protocol

Cryptographic protocol is a communication procedure utilizing the public-key cryptography, for example public-key encryption and digital signature.
We research a broad range of cryptographic protocols as a tool to offer a solution to various security problems from business activities, such as information leakage.
Our recent focus is a signature scheme that provides anonymity of signer, called group signature (cf. press release 1, press release 2 ,Japanese only). We also study a database encryption scheme that enables searches and mathematical operations (e.g. taking a sum) over ciphertexts without decryption as a key-technology to realize a secure cloud computing, and the secret sharing scheme, which enables a secure decentralized control of secret information.

Symmetric Cryptography

Symmetric cryptography forms the basis of IT network's security. In the field of symmetric cryptography, we study the cryptanalysis of existing cipher algorithms and design new cipher algorithms to offer the better security and efficiency. We also study the appropriate usage of block cipher algorithms (e.g. AES), which is known as the block cipher mode of operation, and side-channel attacks against the hardware implementations of cipher algorithms.
As a recent topic, we developed a ultra-lightweight block cipher, called TWINE, to fit the highly resource-constrained devices, such as RFID and low-end micro-controller.
We have two block cipher algorithms (CIPHERUNICORN-A and CIPHERUNICORN-E) included in the recommendation list of CRYPTREC, a crypto standardization effort operated by the Japanese government. In addition, we are proposing an efficient AES-based message authentication code (PC-MAC-AES) for the forthcoming revision of CRYPTREC list. The details on our research are described here.

Error-correcting Code

Error-correcting code (ECC) is a technology to make information transmission over the physical (thus noisy) channel reliable. It consists of an encoding, which append a parity to the message and a decoding, which recovers the original message from the received message with parity.
Due to the recent advance it is becoming practical to deploy the high-performance codes such as Turbo code and Low-Density Parity-Check (LDPC) code. Their error-correcting performances are quite cloth to the optimal (Shannon limit), which proves the growing importance of ECC to the today's communication networks. We are currently focusing on LDPC code for the algorithm and the hardware architecture. The results are widely deployed to microwave, optical, and mobile wireless transmission systems.

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