To provide a stream encryption method and apparatus for realizing initializing processing securely at a high speed even when stream encryption is used under an environment wherein an initial value is frequently updated.
The stream encryption method respectively independently manages an internal state wherein ordinary initializing processing (S11) is finished and an internal state in the case of encryption processing (S13). Thus, the method executes simple initializing processing (S12) at encryption processing (S13), carries out the encryption processing (S13) after the internal state is updated, the internal state is deleted after the end of the encryption processing (S13) to restore the state to the internal state at the end of the ordinary initializing processing.
TANAKA TOSHIAKI
Masatake Shiga
Takashi Watanabe