Abstract. In this paper, we show that two variants of Stern's identification scheme [IEEE Transaction on Information Theory '96] are provably secure against concurrent attack under the assumptions on the worst-case hardness of lattice problems. These assumptions are weaker than those for the previous lattice-based identification schemes of Micciancio and Vadhan [CRYPTO '03] and of Lyubashevsky [PKC '08]. We also construct eAEcient ad hoc anonymous identification schemes based on the lattice problems by modifying the variants.
We describe public key encryption schemes with security provably based on the worst case hardness of the approximate Shortest Vector Problem in some structured lattices, called ideal lattices. Under the assumption that the latter is exponentially hard to solve even with a quantum computer, we achieve CPA-security against subexponential attacks, with (quasi-)optimal asymptotic performance: if n is the security parameter, both keys are of bit-length O(n) and the amortized costs of both encryption and decryption are O(1) per message bit. Our construction adapts the trapdoor one-way function of Gentry et al. (STOC'08), based on the Learning With Errors problem, to structured lattices. Our main technical tools are an adaptation of Ajtai's trapdoor key generation algorithm (ICALP'99) and a re-interpretation of Regev's quantum reduction between the Bounded Distance Decoding problem and sampling short lattice vectors.
Abstract. An unresolved problem in research on authenticated key exchange (AKE) is to construct a secure protocol against advanced attacks such as key compromise impersonation and maximal exposure attacks without relying on random oracles. HMQV, a state of the art AKE protocol, achieves both efficiency and the strong security proposed by Krawczyk (we call it the CK + model), which includes resistance to advanced attacks. However, the security proof is given under the random oracle model. We propose a generic construction of AKE from a key encapsulation mechanism (KEM). The construction is based on a chosen-ciphertext secure KEM, and the resultant AKE protocol is CK + secure in the standard model. The construction gives the first CK + secure AKE protocols based on the hardness of integer factorization problem, code-based problems, or learning problems with errors. In addition, instantiations under the Diffie-Hellman assumption or its variant can be proved to have strong security without non-standard assumptions such as πPRF and KEA1. Furthermore, we extend the CK + model to identity-based (called the id-CK + model), and propose a generic construction of identity-based AKE (ID-AKE) based on identity-based KEM, which satisfies id-CK + security. The construction leads first strongly secure ID-AKE protocols under the hardness of integer factorization problem, or learning problems with errors.
Abstract. We propose multi-bit versions of several single-bit cryptosystems based on lattice problems, the error-free version of the Ajtai-Dwork cryptosystem by Goldreich, Goldwasser, and Halevi [CRYPTO '97], the Regev cryptosystems [JACM 2004 and STOC 2005], and the Ajtai cryptosystem [STOC 2005]. We develop a universal technique derived from a general structure behind them for constructing their multi-bit versions without increase in the size of ciphertexts. By evaluating the trade-off between the decryption errors and the hardness of underlying lattice problems, it is shown that our multi-bit versions encrypt O(log n)-bit plaintexts into ciphertexts of the same length as the original ones with reasonable sacrifices of the hardness of the underlying lattice problems. Our technique also reveals an algebraic property, named pseudohomomorphism, of the lattice-based cryptosystems.
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