Patent ID: 7394902

Claim:
An encryption apparatus for generating an encrypted text by encrypting a plaintext, said encryption apparatus comprising: a storage unit operable to store an encryption key and a parameter, the parameter being adapted to a decryption apparatus and being used to change a probability of decryption error in decrypting the encrypted text; an encryption unit operable to generate the encrypted text from the plaintext, using the encryption key and the parameter stored in said storage unit, according to an encryption algorithm which changes the probability of the decryption error in decrypting the encrypted text depending on a value of the parameter; and an updating unit operable to update the parameter stored in said storage unit, wherein the parameter stored in said storage unit indicates the number of terms whose coefficients indicate 1 in a random number polynomial based on an NTRU encryption method, and wherein said updating unit increases the number of the terms whose coefficients indicate 1 every passage of a predetermined amount of time.