SECRET SHARING SYSTEM, DATA DISTRIBUTION DEVICE, DISTRIBUTED DATA CONVERSION DEVICE, SECRET SHARING METHOD, AND PROGRAM

摘要

A secret sharing system transforms shares in computational secret sharing to shares in homomorphic secret sharing. On a data distribution apparatus, a key selecting part selects K'-1 keys s j . A pseudorandom number generation part generates pseudorandom numbers r j from the keys s j . An encryption part generates a ciphertext c from information a by using the pseudorandom numbers r j . A key division part divides each of the keys s j into N shares f g (n) by using an arbitrary sharing scheme S1. A ciphertext division part divides the ciphertext c into N shares f c (n) by using an arbitrary sharing scheme S0. On each of distributed data transform apparatuses, when K shares f sj (i) are input into the distributed data transform apparatuses, the reconstruction part generates a reconstructed value U j by reconstruction of shares f sj (i) by using the secret sharing scheme S1 and, when K shares f c (i) are input into the distributed data transform apparatuses, the reconstruction part generates the reconstructed value U j by reconstruction of shares f c (i) by using the sharing scheme S0. A redivision part divides the reconstructed value U j into N shares f Uj (n) by using a homomorphic secret sharing scheme S2. A transform part generates a share g a (i) of the information a from K' shares f Uj .