Hitachi Information & Communication Engineering, Ltd.

Takeshi Hosoi

Makoto Honda

Katsuyoshi Harasawa

Shigeto Akutsu

The disclosed is a method for synchronization of the running key that is generated from a shared key and that is used for encryption and decryption in communications encrypted with the shared key using a multi-valued signal. In the method for synchronization, the transmitting node transmits a signal that is formed of a multi-valued signal and that has a predetermined fixed pattern before transmitting data encrypted with the shared key. The receiving node generates a bit discrimination threshold signal that allows for bit discrimination and that has a fixed length, shifts bit by bit the phase of the bit discrimination threshold signal while monitoring bit discrimination with respect to a fixed pattern signal that is to be received, and sets the phase of the bit discrimination threshold signal when the phase of the fixed pattern signal matches the phase of the bit discrimination threshold signal. Then, synchronization of the running key is performed in accordance with the phase that has been set between the transmitting node and the receiving node.

Method for synchronization in encrypted communications using shared key

A transmitting node produces synchronization data to be inserted into plain text and encrypts the thus generated data into multi-valued data so as to transmit the data. The synchronization data indicates the position of a running key used for encryption. A receiving node decrypts a signal including the synchronization data using the running key and detects the synchronization data from the signal to confirm synchronization of the running key between transmitting and receiving nodes. Then, the receiving node transmits a synchronization confirmation signal to the transmitting node. If the transmitting node does not receive the synchronization confirmation signal, it determines that synchronization of the running key is shifted, and re-synchronization is performed. To perform re-synchronization, a running key ahead of the position of the running key associated with synchronization data that has been stored is generated.

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Yokohama, Japan

Takeshi Hosoi