12 research outputs found
An Efficient Adaptive-Deniable-Concurrent Non-malleable Commitment Scheme
It is known that composable secure commitments, that is, concurrent non-malleable commitments exist in the plain model, based only on standard assumptions such as the existence of claw-free permutations or even one-way functions. Since being based on the plain model, the deniability of them is trivially satisfied, and especially the latter scheme satisfies also adaptivity, hence it is adaptive-deniable-concurrent non-malleable. However, those schemes cannot be said to be practically efficient. We show a practically efficient (string) adaptive-deniable-concurrent commitment scheme is possible under a global setup model, called global CRS-KR model
Witness-Indistinguishable Arguments with -Protocols for Bundled Witness Spaces and its Application to Global Identities
We propose a generic construction of a -protocol of commit-and-prove type, which is an AND-composition of -protocols on statements that include a common commitment. Our protocol enables a prover to convince a verifier that the prover knows a bundle of witnesses that have a common component which we call a base witness point. When the component -protocols are of witness-indistinguishable argument systems, our -protocol is also a witness-indistinguishable argument system as a whole. As an application, we propose a decentralized multi-authority anonymous authentication scheme. We first give a syntax and security definitions of the scheme. Then we give a generic construction of the scheme. There a witness is a bundle of witnesses each of which decomposes into a common global identity string and a digital signature on it. We mention an instantiation in the setting of bilinear groups
Fully Homomorphic Encryption for Point Numbers
In this paper, based on the FV scheme, we construct a first fully homomorphic encryption scheme FHE4FX that can homomorphically compute addition and/or multiplication of encrypted fixed point numbers without knowing the secret key. Then, we show that in the FHE4FX scheme one can efficiently and homomorphically compare magnitude of two encrypted numbers. That is, one can compute an encryption of the greater-than bit
that represents whether or not given two ciphertexts and (of and , respectively) without knowing the secret key. Finally we show that these properties of the FHE4FX scheme enables us to construct a fully homomorphic encryption scheme FHE4FL that can homomorphically compute addition and/or multiplication of encrypted floating point numbers
Proofs of Knowledge on Monotone Predicates and its Application to Attribute-Based Identifications and Signatures
We propose a concrete procedure of the -protocol introduced by Cramer, Damgård and Schoenmakers at CRYPTO \u2794, which is for proving knowledge that a set of witnesses satisfies a monotone predicate in witness-indistinguishable way; that is, hiding the assignment of truth in the predicate. We provide a detailed procedure by extending the so-called OR-proof
Short CCA-Secure Attribute-Based Encryption
Chosen-ciphertext attacks (CCA) are typical threat on public-key encryption schemes. We show direct chosen-ciphertext security modification in the case of attribute-based encryption (ABE), where an ABE scheme secure against chosen-plaintext attacks (CPA) is converted into an ABE scheme secure against CCA by individual techniques. Our modification works in the setting that the Diffie-Hellman tuple to be verified in decryption is in the target group of a bilinear map. The employed techniques result in expansion of the secret-key length and the decryption cost by a factor of four, while the public-key and the ciphertext lengths and the encryption cost remain almost the same
Short CCA-Secure Attribute-Based Encryption
Chosen-ciphertext attacks (CCA) are typical threat on public-key encryption schemes. We show direct chosen-ciphertext security modification in the case of attribute-based encryption (ABE), where an ABE scheme secure against chosen-plaintext attacks (CPA) is converted into an ABE scheme secure against CCA by individual techniques. Our modification works in the setting that the Diffie-Hellman tuple to be verified in decryption is in the target group of a bilinear map. The employed techniques result in expansion of the secret-key length and the decryption cost by a factor of four, while the public-key and the ciphertext lengths and the encryption cost remain almost the same
Survey and new idea for attribute-based identification scheme secure against reset attacks
Identification schemes are a common one-way authentication technique for a user to prove himself securely to a verifier. However, it is known that identification schemes based on the sigma-protocol are basically insecure against reset attacks. On the other-hand, attribute-based cryptography is a technique which allows for the secure implementation of access policies within a cryptosystem. In this paper, we report on the developments in the area of reset attacks for identification schemes as well as for attribute-based identification schemes. Then we put together a new idea to construct attribute-based identification schemes secure against reset attacks