PROXY RE-ENCRYPTION SYSTEM, TRANSFER INFORMATION GENERATION DEVICE, TRANSFERRED INFORMATION GENERATION DEVICE, CONVERSION KEY GENERATION DEVICE, CIPHERTEXT CONVERSION DEVICE, PROXY RE-ENCRYPTION METHOD, AND PROGRAM THEREOF

摘要

PROBLEM TO BE SOLVED: To provide a high-safety system which is free of leakage of a conversion key as a proxy re-encryption system applied to a lattice problem-based public key encryption system.;SOLUTION: A conversion key ((i, A_i, P_i), (j, A_j, P_j), T) is generated by calculating T=C-B from (A_i, P_i, B) and (A_j, P_j, C) obtained by calculating R selected at random from a public key (A_i, P_i) and a secret key S_i of a user (i) as a decryption authority transferrer, and a public key (A_j,P_j) and secret keys S_j and Z_q^ng of a user (j) as a decryption authority transferee, and B=R+S_i and C=S_j+R. Then c_i'=c_i-u_iT is calculated from a ciphertext C_i=(u_i, c_i) encrypted with the public key (A_i, P_i) of the user (i) using the conversion key, a mask ciphertext C_j'=(u_j', c_j') is calculated, u_j=u_i+u_j' and c_j=c_i'+c_j' are calculated, and (u_j, c_j) is output as a ciphertext C_j for the user (j).;COPYRIGHT: (C)2012,JPO&INPIT