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RE-ENCRYPTION KEY GENERATOR, RE-ENCRYPTION APPARATUS, ENCRYPTION APPARATUS, DECRYPTION APPARATUS, AND STORAGE MEDIUM

  • US 20160380767A1
  • Filed: 09/09/2016
  • Published: 12/29/2016
  • Est. Priority Date: 10/03/2014
  • Status: Active Grant
First Claim
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1. A re-encryption key generator which generates a re-encryption key needed to obtain re-encrypted text data which is configured to be decrypted by means of a second private key of a second user device, by re-encrypting, without decryption, ciphertext data obtained by encrypting plaintext data by means of a first public key of a first user device, the generator comprising:

  • a first storage circuit configured to store a first private key corresponding to the first public key;

    a second storage circuit configured to store a second re-encryption key generation key of the second user device which is different from a second public key corresponding to the second private key; and

    a re-encryption key generation device configured to generate the re-encryption key based on the first private key, the second re-encryption key generation key, and a plurality of random numbers,wherein the second re-encryption key generation key comprises a plurality of system-specific values and the second private key,the re-encryption key includes an exponent having a numerator portion and a denominator portion or a scalar having a numerator portion and a denominator portion,the numerator portion is in form of a linear coupling of the second private key on which at least one of a plurality of private values specifying a relation between the system-specific values and the random numbers is allowed to act, andthe denominator portion is the first private key.

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