In a proxy re-encryption (PRE) scheme, a semi-trusted proxy can convert a ciphertext under Alice's public key into another ciphertext that Bob can decrypt without accessing the underlying plaintext. This property adds flexibility in various applications, such as cloud data sharing. In this paper, we study CCA-secure, single-hop unidirectional PRE schemes without pairings. We gain high efficiency and public verifiability which enables anyone to publicly verify the validity of the original ciphertexts and re-encrypted ciphertexts. With public verifiability, we can offload the integrity check of the wellformedness of ciphertexts from power-restrained clients to any honest-but-curious untrusted public cloud for improved efficiency.
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