International Association
for Cryptologic Research

Proxy re-encryption (PRE) schemes are cryptosystems which allow a proxy who has a re-encryption key to convert a ciphertext originally encrypted for one party into a ciphertext which can be decrypted by another party. In IWSEC 2011, Hayashi et al. proposed the new security notion for PRE called ``unforgeability of re-encryption keys against collusion attacks,\'\' UFReKey-CA for short. They proposed the PRE schemes and claimed that their schemes meet UFReKey-CA. However, Isshiki et al. pointed out that the schemes do not meet UFReKey-CA in IWSEC 2013. It is an open problem of constructing the scheme which meets UFReKey-CA. In this paper, we propose new PRE schemes which meet confidentiality (RCCA security) assuming that the q-wDBDHI problem is hard and meet UFReKey-CA assuming that the 2-DHI problem is hard.