Hash-based signatures for the internet of things

While numerous digital signature schemes exist in the literature, most real-world system rely on RSA-based signature schemes or on the digital signature algorithm (DSA), including its elliptic curve cryptography variant ECDSA. In this position paper we review a family of alternative signature schemes, based on hash functions, and we make the case for their application in Internet of Things (IoT) settings. Hash-based signatures provide postquantum security, and only make minimal security assumptions, in general requiring only a secure cryptographic hash function. This makes them extremely flexible, as they can be implemented on top of any hash function that satisfies basic security properties. Hash-based signatures also feature numerous parameters defining aspects such as signing speed and key size, that enable trade-offs in constrained environments. Simplicity of implementation and customization make hash based signatures an attractive candidate for the IoT ecosystem, which is composed of a number of diverse, constrained devices

The Design Space of Lightweight Cryptography

International audienceFor constrained devices, standard cryptographic algorithms can be too big, too slow or too energy-consuming. The area of lightweight cryptography studies new algorithms to overcome these problems. In this paper, we will focus on symmetric-key encryption, authentication and hashing. Instead of providing a full overview of this area of research, we will highlight three interesting topics. Firstly, we will explore the generic security of lightweight constructions. In particular, we will discuss considerations for key, block and tag sizes, and explore the topic of instantiating a pseudorandom permutation (PRP) with a non-ideal block cipher construction. This is inspired by the increasing prevalence of lightweight designs that are not secure against related-key attacks, such as PRINCE, PRIDE or Chaskey. Secondly, we explore the efficiency of cryptographic primitives. In particular, we investigate the impact on efficiency when the input size of a primitive doubles. Lastly, we provide some considerations for cryptographic design. We observe that applications do not always use cryptographic algorithms as they were intended, which negatively impacts the security and/or efficiency of the resulting implementations

The Design Space of Lightweight Cryptography

For constrained devices, standard cryptographic algorithms can be too big, too slow or too energy-consuming. The area of lightweight cryptography studies new algorithms to overcome these problems. In this paper, we will focus on symmetric-key encryption, authentication and hashing. Instead of providing a full overview of this area of research, we will highlight three interesting topics. Firstly, we will explore the generic security of lightweight constructions. In particular, we will discuss considerations for key, block and tag sizes, and explore the topic of instantiating a pseudorandom permutation (PRP) with a non-ideal block cipher construction. This is inspired by the increasing prevalence of lightweight designs that are not secure against related-key attacks, such as PRINCE, PRIDE or Chaskey. Secondly, we explore the efficiency of cryptographic primitives. In particular, we investigate the impact on efficiency when the input size of a primitive doubles. Lastly, we provide some considerations for cryptographic design. We observe that applications do not always use cryptographic algorithms as they were intended, which negatively impacts the security and/or efficiency of the resulting implementations

High-Performance Ideal Lattice-Based Cryptography on 8-bit ATxmega Microcontrollers

Over the last years lattice-based cryptography has received much attention due to versatile average-case problems like Ring-LWE or Ring-SIS that appear to be intractable by quantum computers. But despite of promising constructions, only few results have been published on implementation issues on very constrained platforms. In this work we therefore study and compare implementations of Ring-LWE encryption and the bimodal lattice signature scheme (BLISS) on an 8-bit Atmel ATxmega128 microcontroller. Since the number theoretic transform (NTT) is one of the core components in implementations of lattice-based cryptosystems, we review the application of the NTT in previous implementations and present an improved approach that significantly lowers the runtime for polynomial multiplication. Our implementation of Ring-LWE encryption takes 27 ms for encryption and 6.7 ms for decryption. To compute a BLISS signature, our software takes 329 ms and 88 ms for verification. These results outperform implementations on similar platforms and underline the feasibility of lattice-based cryptography on constrained devices

Multi-Armed SPHINCS+

Hash-based signatures are a type of Digital Signature Algorithms that are positioned as one of the most solid quantum-resistant constructions. As an example SPHINCS+, has been selected as a standard during the NIST Post-Quantum Cryptography competition. However, hash-based signatures suffer from two main drawbacks: signature size and slow signing process. In this work, we give a solution to the latter when it is used in a mobile device. We take advantage of the fact that hash-based signatures are highly parallelizable. More precisely, we provide an implementation of SPHINCS+ on the Snapdragon 865 Mobile Platform taking advantage of its eight CPUs and their vector extensions. Our implementation shows that it is possible to have a speed-up of 15 times when compared to a purely sequential and non-vectorized implementation. Furthermore, we evaluate the performance impact of side-channel protection using vector extensions in the SPHINCS+ version based on SHAKE

Brandt's fully private auction protocol revisited

International audienceAuctions have a long history, having been recorded as early as 500 B.C. [Kri02]. Nowadays, electronic auctions have been a great success and are increasingly used in various applications, including high performance computing [BAGS02]. Many cryptographic protocols have been proposed to address the various security requirements of these electronic transactions, in particular to ensure privacy. Brandt [Bra06] developed a protocol that computes the winner using homomorphic operations on a distributed ElGamal encryption of the bids. He claimed that it ensures full privacy of the bidders, i.e. no information apart from the winner and the winning price is leaked. We first show that this protocol – when using malleable interactive zero-knowledge proofs – is vulnerable to attacks by dishonest bidders. Such bidders can manipulate the publicly available data in a way that allows the seller to deduce all participants' bids. We provide an efficient parallelized implementation of the protocol and the attack to show its practicality. Additionally we discuss some issues with verifiability as well as attacks on non-repudiation, fairness and the privacy of individual bidders exploiting authentication problems

G-Merkle: A Hash-Based Group Signature Scheme From Standard Assumptions

Hash-based signature schemes are the most promising cryptosystem candidates in a post-quantum world, but offer little structure to enable more sophisticated constructions such as group signatures. Group signatures allow a group member to anonymously sign messages on behalf of the whole group (as needed for anonymous remote attestation). In this work, we introduce G-Merkle, the first (stateful) hash-based group signature scheme. Our proposal relies on minimal assumptions, namely the existence of one-way functions, and offers performance equivalent to the Merkle single-signer setting. The public key size (as small as in the single-signer setting) outperforms all other post-quantum group signatures. Moreover, for $N$ group members issuing at most $B$ signatures each, the size of a hash-based group signature is just as large as a Merkle signature with a tree composed by $N\cdot B$ leaf nodes. This directly translates into fast signing and verification engines. Different from lattice-based counterparts, our construction does not require any random oracle. Note that due to the randomized structure of our Merkle tree, the signature authentication paths are pre-stored or deduced from a public tree, which seems a requirement hard to circumvent. To conclude, we present implementation results to demonstrate the practicality of our proposal

Efficient 4-way Vectorizations of the Montgomery Ladder

We propose two new algorithms for 4-way vectorization of the well known Montgomery ladder over elliptic curves of Montgomery form. The first algorithm is suitable for variable base scalar multiplication. In comparison to the previous work by Hisil et al. (2020), it eliminates a number of non-multiplication operations at the cost of a single multiplication by a curve constant. Implementation results show this trade-off to be advantageous. The second algorithm is suitable for fixed base scalar multiplication and provides clear speed improvement over a previous vectorization strategy due to Costigan and Schwabe (2009). The well known Montgomery curves Curve25519 and Curve448 are part of the TLS protocol, version~1.3. For these two curves, we provide constant time assembly implementations of the new algorithms. Additionally, for the algorithm of Hisil et al. (2020), we provide improved implementations for Curve25519 and new implementation for Curve448. Timings results on the Haswell and Skylake processors indicate that in practice the new algorithms are to be preferred over previous methods for scalar multiplication on these curves

Cryptographic Role-Based Access Control, Reconsidered

A significant shortcoming of traditional access control mechanisms is their heavy reliance on reference monitors. Being single points of failure, monitors need to run in protected mode and have permanent online presence in order to handle all access requests. Cryptographic access control offers an alternative solution that provides better scalability and deployability. It relies on security guarantees of the underlying cryptographic primitives and the appropriate key distribution/management in the system. In order to rigorously study security guarantees that a cryptographic access control system can achieve, providing formal security definitions for the system is of great importance, since the security guarantee of the underlying cryptographic primitives cannot be directly translated into those of the system. In this paper, we follow the line of the existing studies on the cryptographic enforcement of Role-Based Access Control (RBAC). Inspired by the study focusing on the relation between the existing security definitions for such systems, we identify two types of attacks not described in the existing works. Therefore, we propose two new security definitions with the goal of appropriately modeling cryptographic enforcement of Role-Based Access Control policies and studying the relation between our new definitions and the existing ones. In addition, we show that the cost of supporting dynamic policy updates is inherently expensive by presenting two lower bounds for such systems that guarantee correctness and secure access

Optimization of LPN Solving Algorithms

In this article we focus on constructing an algorithm that automatizes the generation of LPN solving algorithms from the considered parameters. When searching for an algorithm to solve an LPN instance, we make use of the existing techniques and optimize their use. We formalize an LPN algorithm as a path in a graph G and our algorithm is searching for the optimal paths in this graph. The results bring improvements over the existing work by a factor from 2^8 to 2^{10}, i.e. we improve the results of the covering code from ASIACRYPT\u2714. Furthermore, we propose concrete practical codes and a method to find good codes