In this paper, a new construction of adaptive and composable transcoders from universally composabley secure (the uc-security) commitments is introduced and analyzed. Our transcoder is built on the top of scalable video coding standard, known as H.264/SVC. The idea behind of our implementation is simple: a base layer of streams is encoded by an extractable key while an enhanced layer of streams is encoded by an equivocable key of the underlying universally composable commitment scheme. We show that our construction reaches the UC-security in the presence of adaptive adversaries in the common reference string model assuming that the underlying Paillier's public-key encryption scheme is semantically secure and the Damgård-Fazio-Nicolosi's non-interactive protocol is zero-knowledge in the registered public-key model. Furthermore, if the underlying Paillier's public-key encryption scheme is replaced by Damgård-Jurik's length-flexible public key encryption scheme, then the derived adaptive and composable transcoder is length-flexible as well.
In this paper, a new construction of adaptive and composable transcoders from universally composabley secure (the uc-security) commitments is introduced and analyzed. Our transcoder is built on the top of scalable video coding standard, known as H.264/SVC. The idea behind of our implementation is simple: a base layer of streams is encoded by an extractable key while an enhanced layer of streams is encoded by an equivocable key of the underlying universally composable commitment scheme. We show that our construction reaches the UC-security in the presence of adaptive adversaries in the common reference string model assuming that the underlying Paillier's public-key encryption scheme is semantically secure and the Damgård-Fazio-Nicolosi's non-interactive protocol is zero-knowledge in the registered public-key model. Furthermore, if the underlying Paillier's public-key encryption scheme is replaced by Damgård-Jurik's length-flexible public key encryption scheme, then the derived adaptive and composable transcoder is length-flexible as well.
Universal composability (or UC security) provides very strong security guarantees for protocols that run in complex real-world environments. In particular, security is guaranteed to hold when the protocol is run concurrently many times with other secure and possibly insecure protocols. Commitment schemes are a basic building block in many cryptographic constructions, and as such universally composable commitments are of great importance in constructing UC-secure protocols. In this paper, we construct highly efficient UC-secure commitments from the standard DDH assumption, in the common reference string model. Our commitment stage is non-interactive, has a common reference string with O(1) group elements, and has complexity of O(1) exponentiations for committing to a group element (to be more exact, the effective cost is that of 23 1 exponentiations overall, for both the commit and decommit stages). We present 3 a construction that is secure in the presence of static adversaries, and a construction that is secure in the presence of adaptive adversaries with erasures, where the latter construction has an effective additional cost of just 5 1 3 exponentiations. 1
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.
In this work, we study the intrinsic complexity of black-box Universally Composable (UC) secure computation based on general assumptions. We present a thorough study in various corruption mod-elings while focusing on achieving security in the common reference string (CRS) model. Our results involve the following: • Static UC secure computation. Designing the first static UC secure oblivious transfer protocol based on public-key encryption and stand-alone semi-honest oblivious transfer. As a corollary we obtain the first black-box constructions of UC secure computation assuming only two-round semi-honest oblivious transfer. • One-sided UC secure computation. Designing adaptive UC secure two-party computation with single corruptions assuming public-key encryption with oblivious ciphertext generation. • Adaptive UC secure computation. Designing adaptively secure UC commitment scheme assum-ing only public-key encryption with oblivious ciphertext generation. As a corollary we obtain the first black-box constructions of adaptive UC secure computation assuming only (trapdoor) simu-latable public-key encryption (as well as a variety of concrete assumptions). We remark that such a result was not known even under non-black-box constructions.
We present a general framework for constructing non-interactive universally composable (UC) commitment schemes that are secure against adaptive adversaries in the non-erasure setting under a single re-usable common reference string. Previously, such “fully-equipped ” UC commitment schemes are only known in [8, 9], with an unavoidable overhead of O(κ) in the sense of communication and computational complexities; meaning that to commit λ bits, the communication and computational costs require O(λκ), where κ denotes the security parameter. Efficient construction of a fully-equipped UC commitment scheme was a long-standing open problem. We introduce a cryptographic primitive, called all-but-many encryptions (ABMEs), and prove that it is a translation of fully-equipped UC commitment in the primitive level. We then construct ABMEs from cryptographic primitives that we call a probabilistic pseudo random function family and extractable sigma protocols – the former is a probabilistic version of a pseudo random function family and the latter is a special kind of sigma (i.e., canonical 3-round public-coin HVSZK) protocols with some extractability. We provide fully-equipped UC commitment schemes from ABMEs under DDH and DCR-based assumptions, respectively. In particular, the DCR-based scheme is the first fully-equipped UC commitment scheme with optimal expansion factor Ω(1); to commit κ bits, the communication and computational costs are Ω(κ). We further construct a fully-equipped UC commitment scheme from a general assumption (in which trap-door permutations exist), which is far more efficient than the previous construction [9], because, unlike [9], our construction does not require non-interactive zero-knowledge proof systems. 1
The universal composability (UC) framework enables the modular design of cryptographic protocols by allowing arbitrary compositions of lower-level building blocks. Public-key encryption is unarguably a very important such building block. However, so far no UC-functionality exists that offers non-interactive encryption necessary for modular protocol construction. We provide an ideal functionality for non-committing encryption (i.e., public-key encryption secure against adaptive corruptions) with locally generated, and therefore non-interactive, ciphertexts. As a sanity check, we also provide a property-based security notion that we prove to be equivalent to the UC notion. We then show that the encryption scheme of Camenisch et al. (SCN '16) based on trapdoor permutations securely implements our notion in the random-oracle model without assuming secure erasures. This is the best one can hope to achieve as standard-model constructions do not exist due to the uninstantiability of round-optimal adaptively secure message transfer in the standard model (Nielsen, Crypto '02). We illustrate the modular reusability of our functionality by constructing the first non-interactive signcryption scheme secure against adaptive corruptions without secure erasures in the UC framework.
We present a general framework for constructing non-interactive universally composable (UC) commitment schemes that are secure against adaptive adversaries in the non-erasure model under a re-usable common reference string. Previously, such “fully-equipped” UC commitment schemes have been known only in [CF01,CLOS02], with strict expansion factor O(κ); meaning that to commit λ bits, communication strictly requires O(λκ) bits, where κ denotes the security parameter. Efficient construction of a fully-equipped UC commitment scheme is a long-standing open problem. We introduce new abstraction, called all-but-many encryption (ABME), and prove that it captures fully-equipped UC commitment schemes. We propose the first fully-equipped UC commitment scheme with optimal expansion factor O(1) from our ABME scheme related to the DCR assumption. We also provide an all-but-many lossy trapdoor function (ABM-LTF) [Hof12] from our DCR-based ABME scheme, with a better lossy rate than [Hof12].