Analysis And Improvement Of Conditional Proxy Re-Encryption Scheme Based On Secret Sharing

Proxy re-encryption became hot topic in cryptography research area recent years,and widely applied on occasions such like digital copyright protection, encrypted email forward,cloud computing etc. In traditional proxy re-encryption system, the proxy can transfer alldelegator’s ciphertexts to delegatee’s ciphertexts, which means that the delegator cannot controlproxy’s delegation in a fine-grained level. To improve this, Weng et al. constructed an efficientCCA-secure conditional proxy re-encryption. Currently all the proposed schemes can onlysupport simple “AND” operation which limited application ability. Recently, Lan et al. proposeda new condition proxy re-encryption scheme on secret sharing, and claimed that their schemesupports multiple conditions "AND" and "OR" operation meanwhile obtaining the security ofindistinguishability against chosen-ciphertext attacks in random oracle model. However, bygiving two concrete attacks, the essay indicates that Lan et al.’s scheme cannot obtainIND-CPRE-CCA security as they claimed. The second attack indicates that Lan et al.’s schemecannot even obtain IND-CPA security. In order to satisfy "AND" and "OR" operation meanwhilepreventing the two attacks mentioned above, the essay proposed an improved conditional proxyre-encryption scheme based on Lan et al.’s scheme, analyzed the security of the new scheme indetail, and point out the reason why the new scheme can defend the two attacks. However, theonly drawback is that the new scheme can only reach IND-CCA1security. It needs further studyand research to improve the scheme to IND-CCA2security.