2003 | OriginalPaper | Buchkapitel
Chosen-Ciphertext Security without Redundancy
verfasst von : Duong Hieu Phan, David Pointcheval
Erschienen in: Advances in Cryptology - ASIACRYPT 2003
Verlag: Springer Berlin Heidelberg
Enthalten in: Professional Book Archive
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We propose asymmetric encryption schemes for which all ciphertexts are valid (which means here “reachable”: the encryption function is not only a probabilistic injection, but also a surjection). We thus introduce the Full-Domain Permutation encryption scheme which uses a random permutation. This is the first IND-CCA cryptosystem based on any trapdoor one-way permutation without redundancy, and more interestingly, the bandwidth is optimal: the ciphertext is over k more bits only than the plaintext, where 2 − k is the expected security level. Thereafter, we apply it into the random oracle model by instantiating the random permutation with a Feistel network construction, and thus using OAEP. Unfortunately, the usual 2-round OAEP does not seem to be provably secure, but a 3-round can be proved IND-CCA even without the usual redundancy $m || 0^{k_1}$, under the partial-domain one-wayness of any trapdoor permutation. Although the bandwidth is not as good as in the random permutation model, absence of redundancy is quite new and interesting: many implementation risks are ruled out.