Identity-based re-encryption scheme with lightweight re-encryption key generation

Abstract

Cryptographic proxy re-encryption is a very useful primitive which is capable of transforming a ciphertext under one public key PK1 into a new ciphertext under another public key PK2 without private information leakage, while the two ciphertexts are encryptions of the same message. Re-encryption schemes at first are constructed under the public-key encryption (PKE) scenario. While it is a powerful primitive naturally required in not only PKE but also other scenarios, various extensions from PKE to other advanced encryption schemes like identity-based encryption (IBE), attribute-based encryption (ABE) as well as functional encryption (FE) are needed as well. In this work we have concentrated on how to reduce the workloads in the user/client side at large. To this end, we have put forth a novel identity-based proxy re-encryption (IBPRE) scheme with the feature that the re-encryption key gen­eration for the users is highly lightweight - actually almost free. Although this will lead to possibly extra decryption workload due to the utilization of homomorphic encryption, it is the first scheme realizing such almost free RK generation. In addition, it can also avoid some other shortcomings like re-encryption key management.