Privacy is a major concern in designing any cryptographic primitive when frequent transactions are done electronically. During electronic transactions, people reveal their personal data into several servers and believe that this information does not leak too much about them. The adaptive oblivious transfer with hidden access policy (AOT-HAP) takes measure against such privacy issues. The existing AOT-HAP involves a sender and multiple receivers apart from a designated issuer. Security of these schemes rely on the fact that the issuer cannot collude with a set of receivers. Moreover, they loose security when run with multiple protocol instances during concurrent execution. We present the first issuer-free AOT-HAP in universal composable (UC) framework in which the protocol is secure even when composed with each other or with other protocols. A concrete security analysis is given assuming the hardness of q-strong Diffie-Hellman (SDH), decision Linear (DLIN) and decision bilinear Diffie-Hellman (DBDH) problems against malicious adversary in UC model. Moreover, the protocol outperforms the existing similar schemes.
Oblivious Transfer (OT) is a fundamental cryptographic protocol that finds a number of applications, in particular, as an essential building block for two-party and multi-party computation. We construct a round-optimal (2 rounds) universally composable (UC) protocol for oblivious transfer secure against active adaptive adversaries from any OW-CPA secure public-key encryption scheme with certain properties in the random oracle model (ROM). In terms of computation, our protocol only requires the generation of a public/secret-key pair, two encryption operations and one decryption operation, apart from a few calls to the random oracle. In~terms of communication, our protocol only requires the transfer of one public-key, two ciphertexts, and three binary strings of roughly the same size as the message. Next, we show how to instantiate our construction under the low noise LPN, McEliece, QC-MDPC, LWE, and CDH assumptions. Our instantiations based on the low noise LPN, McEliece, and QC-MDPC assumptions are the first UC-secure OT protocols based on coding assumptions to achieve: 1) adaptive security, 2) optimal round complexity, 3) low communication and computational complexities. Previous results in this setting only achieved static security and used costly cut-and-choose techniques.Our instantiation based on CDH achieves adaptive security at the small cost of communicating only two more group elements as compared to the gap-DH based Simplest OT protocol of Chou and Orlandi (Latincrypt 15), which only achieves static security in the ROM.
Oblivious Transfer (OT) is a fundamental building block for secure computation, in which a sender holds two messages and a receiver learns exactly one of them, without revealing which one was chosen and without learning the other. While generic constructions for Universally Composable (UC) OT exist, instantiating them from post-quantum assumptions remains challenging, particularly under adaptive corruption. In this work, we present the first adaptively UC-secure OT protocol based on Group Actions, specifically assuming weakly pseudorandom Effective Group Actions (EGA) like CSIDH. We adhere to the framework of [BC15], which derives an adaptively UC-secure OT protocol from SPHF-friendly extractable and equivocable ( ⋿ 2 ) commitment schemes. The central challenge in instantiating this construction from group actions is the lack of SPHF-friendly IND-CCA encryption. Classical CCA transformations such as Fujisaki-Okamoto destroy the algebraic structure required for building SPHFs over ciphertexts, while known group action-based schemes offer no native mechanism to prove ciphertext validity. To overcome this obstacle, we construct from group actions an IND-CCA encryption scheme with enough algebraic structure to efficiently recognize valid ciphertexts. Our contributions are threefold: (1) a verifiable chameleon hash function with perfect soundness in the standard model, (2) an SPHF-friendly, publicly verifiable IND-CCA encryption scheme in the random oracle model, and (3) we combine these to build an SPHF-friendly ⋿ 2 commitment scheme and derive a fully adaptively secure OT protocol in the UC framework. This is the first construction of its kind under group action assumptions, enabling post-quantum secure OT with adaptive security guarantees. These building blocks may also be of independent interest e.g., to obtain digital signatures, non-malleable commitment schemes, or verifiable encryption.
Non-committing encryption achieved only semantic security,in contrast,applications often require security against chosen ciphertext attacks.A main ingredient in the previous adaptive universally composable(UC)oblivious transfer protocols are non-committing encryptions.the previous proposals are not UC secure against adaptive adversaries in the so-called non-erase model.A new UC secure oblivious transfer protocols were proposed and schemes utilize two primitives of the verifiably smooth projective hashing and deniable encryption as constructed by.the double trapdoor decryption mechanism based on trapdoor commitment.Our construction is based on the decisional composite residuosity in common reference string (CRS) model.We constructed a two-message(1-round) string oblivious transfer protocol,which improves computational efficient that supports message spaces of size exponential and save O(n)-1 rounds communications efficient than bit-OT protocols.
Authenticationis the first defence line to prevent malicious entities to accesssmart mobile devices(or SMD). Essentially, there exist many available cryptographic primitives to design authentication protocols.Oblivious transfer() protocol is one of the important cryptographic primitives to design authentication protocols. The first lattice‐based framework under universal composability (UC) model was designed by dual mode encryption and promoted us to find an alternative efficient scheme. We note that “lossy encryption” scheme is an extension of the dual mode encryption and can be used to design UC‐secure protocol, but the investigations of via lossy encryption over the lattice are absent. Hence, in order to obtain an efficient authentication protocol by improving the performance of the UC‐secure protocol, in this paper, we first design a multibit lossy encryption under the decisional learning with errors () assumption and then design a new variant of UC‐secure protocol for authenticated protocol via lossy encryption scheme. Additionally, our protocol is secure against semihonest (static) adversaries in the common reference string (CRS) model and within the UC framework.