Encryption apparatus, decryption apparatus and encryption system

A decryption apparatus for decrypting an encrypted text, comprising:

• a decryption unit operable to generate a decrypted text using a decryption key, from the encrypted text generated according to an encryption algorithm which changes a probability of decryption error in decrypting the encrypted text depending on a value of a parameter;
• a judgment unit operable to judge whether or not the decrypted text is obtained correctly;
• a decryption key updating request unit operable to request an encryption apparatus to update the decryption key, according to a result of the judgment made by the judgment unit;
• and
• a parameter initialization request unit operable to request the encryption apparatus to change the value of the parameter to an initial value which decreases the probability of the decryption error in decrypting the encrypted text to a value less than or equal to a predetermined value.

An encryption system comprising an encryption apparatus for generating an encrypted text by encrypting a plaintext and a decryption apparatus for generating a decrypted text by decrypting the encrypted text,

• wherein the encryption apparatus includes:
• a storage unit operable to store an encryption key and a parameter which is adapted to the decryption apparatus and changes 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 the 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 the storage unit, and
• the decryption apparatus includes:
• a decryption unit operable to generate a decrypted text from the encrypted text using a decryption key;
• a decryption key updating request unit operable to request the encryption apparatus to update the decryption key;
• and
• a parameter initialization request unit operable to request the encryption apparatus to change the value of the parameter to an initial value which decreases the probability of the decryption error to a value less than or equal to a predetermined value.

A decryption method for decrypting an encrypted text, comprising:

• a decryption step of generating a decrypted text using a decryption key, from the encrypted text generated according to an encryption algorithm which changes a probability of decryption error in decrypting the encrypted text depending on a value of a parameter;
• a judgment step of judging whether or not the decrypted text is obtained correctly;
• an updating request step of requesting an encryption apparatus to update the decryption key, according to a result of the judgment in the judgment step;
• and
• an initialization request step of requesting the encryption apparatus to change the value of the parameter to an initial value which decreases the probability of decryption error to a value less than or equal to a predetermined value, according to the result of the judgment in the judgment step.

A decryption program for decrypting an encrypted text, causing a computer to execute the following steps of:

• a decryption step of generating a decrypted text using a decryption key, from the encrypted text generated according to an encryption algorithm which changes a probability of decryption error in decrypting the encrypted text depending on a value of a parameter;
• a judgment step of judging whether or not the decrypted text is obtained correctly;
• an updating request step of requesting an encryption apparatus to update the decryption key, according to a result of the judgment in the judgment step;
• and
• an initialization request step of requesting the encryption apparatus to change the value of the parameter to an initial value which decreases the probability of the decryption error to a value less than or equal to a predetermined value, according to the result of the judgment in the judgment step.

A computer-readable storage medium on which an encryption program for generating an encrypted text by encrypting a plaintext is recorded,

• wherein the encryption program comprises:
• an encrypted text generation step of generating the encrypted text from the plaintext, using an encryption key and a parameter, according to an encryption algorithm which changes a probability of decryption error in decrypting the encrypted text depending on a value of the parameter adapted to a decryption apparatus;
• and
• an updating step of updating the parameter.

A computer-readable storage medium on which a decryption program for decrypting an encrypted text is recorded,

• wherein the decryption program comprises:
• a decryption step of generating a decrypted text using a decryption key, from the encrypted text generated according to an encryption algorithm which changes a probability of decryption error in decrypting the encrypted text depending on a value of a parameter;
• a judgment step of judging whether or not the decrypted text is obtained correctly;
• an updating request step of requesting an encryption apparatus to update the decryption key, according to a result of the judgment in the judgment step;
• and
• an initialization request step of requesting the encryption apparatus to change the value of the parameter to an initial value which decreases the probability of the decryption error to a value less than or equal to a predetermined value, according to the result of the judgment in the judgment step.