| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for power remainder calculation capable of preventing side channel attack and attains excellent high speed performance and the excellent reduction of memory use. SOLUTION: The decoding method for obtaining a plaintext m from a secret exponent d, a public key n, and a ciphertext c in a public key cipher includes the steps of: converting the ciphertext c into a randomized ciphertext t; converting the randomized ciphertext t into a randomized plaintext u; and converting the randomized plaintext u into the plaintext m. The step for conversion into the randomized ciphertext t includes a step of generating a random number r and a step of conversion into the randomized ciphertext t by using the random number r and an integer s derived from the random number r. The step for conversion into the randomized plaintext u includes a step of calculating the randomized plaintext u by using a value derived from the secret exponent d. The step for conversion into the plaintext m includes a step of multiplying the randomized plaintext u by the integer s. COPYRIGHT: (C)2005,JPO&NCIPI
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