1,721,003 research outputs found
A Family of FDH Signature Schemes Based on the Quadratic Residuosity Assumption
No full textSignature schemes are arguably the most crucial cryptographic primitive, and devising tight security proofs for signature schemes is an important endeavour, as it immediately impacts the feasibility of deployment in real world applications. Hash-then-sign signature schemes in the Random Oracle Model, such as RSA-FDH, and Rabin-Williams variants are among the fastest schemes to date, but that unfortunately do not enjoy tight security proofs based on the one-wayness of their trapdoor function; instead, all known tight proofs rely on variants of the (non-standard) Φ-Hiding assumption. As our main contribution, we introduce a family of hash-then-sign signature schemes, inspired by a lossy trapdoor function from Freeman et al. (JoC’ 13), that is tightly secure under the Quadratic Residuosity assumption. Our first scheme has the property of having unique signatures, while the second scheme is deterministic with an extremely fast signature verification, requiring at most 3 modular multiplications.</p
On Ciphers that Continuously Access the Non-Volatile Key
Full text linkDue to the increased use of devices with restricted resources such as limited area size, power or energy, the community has developed various techniques for designing lightweight ciphers. One approach that is increasingly discussed is to use the cipher key that is stored on the device in non-volatile memory not only for the initialization of the registers but during the encryption/decryption process as well. Recent examples are the ciphers Midori (Asiacrypt’15) and Sprout (FSE’15). This may on the one hand help to save resources, but also may allow for a stronger key involvement and hence higher security. However, only little is publicly known so far if and to what extent this approach is indeed practical. Thus, cryptographers without strong engineering background face the problem that they cannot evaluate whether certain designs are reasonable (from a practical point of view) which hinders the development of new designs.
In this work, we investigate this design principle from a practical point of view. After a discussion on reasonable approaches for storing a key in non-volatile memory, motivated by several commercial products we focus on the case that the key is stored in EEPROM. Here, we highlight existing constraints and derive that some designs, based on the impact on their throughput, are better suited for the approach of continuously reading the key from all types of non-volatile memory. Based on these findings, we improve the design of Sprout for proposing a new lightweight stream cipher that (i) has a significantly smaller area size than almost all other stream ciphers and (ii) can be efficiently realized using common non-volatile memory techniques. Hence, we see our work as an important step towards putting such designs on a more solid ground and to initiate further discussions on realistic designs
Big Bias Hunting in Amazonia:Large-Scale Computation and Exploitation of RC4 Biases (Invited Paper)
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Cryptanalysis of the DECT Standard Cipher
Full text linkThe DECT Standard Cipher (DSC) is a proprietary 64-bit stream cipher based on irregularly clocked LFSRs and a non-linear output combiner. The cipher is meant to provide confidentiality for cordless telephony. This paper illustrates how the DSC was reverse-engineered from a hardware implementation using custom firmware and information on the structure of the cipher gathered from a patent. Beyond disclosing the DSC, the paper proposes a practical attack against DSC that recovers the secret key from 215 keystreams on a standard PC with a success rate of 50% within hours; somewhat faster when a CUDA graphics adapter is available
Pairing-friendly twisted Hessian curves
No full textThis paper presents efficient formulas to compute Miller doubling and Miller addition utilizing degree-3 twists on curves with j-invariant 0 written in Hessian form. We give the formulas for both odd and even embedding degrees and for pairings on both G 1 × G 2 and G 2 × G 1 . We propose the use of embedding degrees 15 and 21 for 128-bit and 192-bit security respectively in light of the NFS attacks and their variants. We give a comprehensive comparison with other curve models; our formulas give the fastest known pairing computation for embedding degrees 15, 21, and 24. </p
Solving LPN Using Covering Codes
No full textWe present a new algorithm for solving the LPN problem. The algorithm has a similar form as some previous methods, but includes a new key step that makes use of approximations of random words to a nearest codeword in a linear code. It outperforms previous methods for many parameter choices. In particular, we can now solve instances suggested for 80-bit security in cryptographic schemes like HB variants, LPN-C and Lapin, in less than 2(80) operations
A Unified Approach to MPC with Preprocessing Using OT
Full text linkSPDZ, TinyOT and MiniMAC are a family of MPC protocols based on secret sharing with MACs, where a preprocessing stage produces multiplication triples in a finite field. This work describes new protocols for generating multiplication triples in fields of characteristic two using OT extensions. Before this work, TinyOT, which works on binary circuits, was the only protocol in this family using OT extensions. Previous SPDZ protocols for triples in large finite fields require somewhat homomorphic encryption, which leads to very inefficient runtimes in practice, while no dedicated preprocessing protocol for MiniMAC (which operates on vectors of small field elements) was previously known. Since actively secure OT extensions can be performed very efficiently using only symmetric primitives, it is highly desirable to base MPC protocols on these rather than expensive public key primitives. We analyze the practical efficiency of our protocols, showing that they should all perform favorably compared with previous works; we estimate our protocol for SPDZ triples in F240 will perform around 2 orders of magnitude faster than the best known previous protocol
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