The rapid advancement of quantum computing has ushered in a new era of post-quantum cryptography, urgently demanding quantum-resistant digital signatures to secure modern communications and transactions. Among NIST-standardized candidates, Falcon—a compact lattice-based signature scheme—stands out for its suitability in size-sensitive applications. In this paper, we present cuFalcon, a high-throughput GPU implementation of Falcon that addresses its computational bottlenecks through adaptive...

Physical side-channel analysis (SCA) operates on the foundational assumption of access to known plaintext or ciphertext. However, this assumption can be easily invalidated in various scenarios, ranging from common encryption modes like Cipher Block Chaining (CBC) to complex hardware implementations, where such data may be inaccessible. Blind SCA addresses this challenge by operating without the knowledge of plaintext or ciphertext. Unfortunately, prior such approaches have shown limited...

Meet-in-the-middle (MitM) is a powerful approach for the cryptanalysis of symmetric primitives. In recent years, MitM has led to many improved records about key recovery, preimage and collision attacks with the help of automated tools. However, most of the previous work target $\texttt{AES}$-like hashing where the linear layer is an MDS matrix. And we observe that their automatic model for MDS matrix is not suitable for primitives using a binary matrix as their linear layer. In this...

We introduce a new approach between classical security proofs of modes of operation and dedicated security analysis for known cryptanalysis families: General Practical Cryptanalysis. This allows us to analyze generically the security of the sum of two keyed permutations against known attacks. In many cases (of course, not all), we show that the security of the sum is strongly linked to that of the composition of the two permutations. This enables the construction of beyond-birthday bound...

This work investigates persistent fault analysis on ASCON cipher that has been recently standardized by NIST USA for lightweight cryptography applications. In persistent fault, the fault once injected through RowHammer injection techniques, exists in the system during the entire encryption phase. In this work, we propose a model to mount persistent fault analysis (PFA) on ASCON cipher. In the finalization round of the ASCON cipher, we identify that the fault-injected S-Box operation...

Quantum computing has attracted substantial attention from researchers across various fields. In case of the symmetric key cryptography, the main problem is posed by the application of Grover's search. In this work, we focus on quantum analysis of the lightweight block cipher LED. This paper proposes an optimized quantum circuit for LED, minimizing the required number of qubits, quantum gates, and circuit depth. Furthermore, we conduct Grover's attack and Search with Two Oracles (STO)...

We present a novel protocol for two-party ECDSA that achieves two rounds (a single back-and-forth communication) at the cost of a single oblivious linear function evaluation (OLE). In comparison, the previous work of [DKLs18] (S&P 2018) achieves two rounds at the cost of three OLEs, while [BHL24] (EUROCRYPT 2025) requires expensive zero-knowledge proofs on top of the OLE. We demonstrate this by proving that in the generic group model, any adversary capable of generating forgeries for our...

The notion of space hardness serves as a quantitative measure to characterize the resilience of dedicated white-box schemes against code-lifting attacks, making it a widely utilized metric in the field. However, achieving strong space hardness (SSH) under the adaptively chosen-space attack model (ACSAM) remains an unresolved challenge, as no existing white-box scheme has given SSH guarantees under ACSAM. \par To address the problem, we introduce a novel mode of operation tailored for...

We propose a dynamic, low-latency encrypted multi-map (EMM) that operates in two modes: low-leakage mode, which reveals minimal information such as data size, expected response length, and query arrival rate; and subliminal mode, which reveals only the data size while hiding metadata including query and update times, the number of operations executed, and even whether an operation was executed at all---albeit at the cost of full correctness. We achieve this by exploiting a tradeoff...

XCB, a tweakable enciphering mode, is part of IEEE Std. 1619.2 for shared storage media. We show that all versions of XCB are not secure through three plaintext recovery attacks. A key observation is that XCB behaves like an LRW1-type tweakable block cipher for single-block messages, which lacks CCA security. The first attack targets one-block XCB, using three queries to recover the plaintext. The second one requires four queries to recover the plaintext that excludes one block. The last one...

In this paper, we explore a new type of key collisions called target-plaintext key collisions of AES, which emerge as an open problem in the key committing security and are directly converted into single-block collision attacks on Davies-Meyer (DM) hashing mode. For this key collision, a ciphertext collision is uniquely observed when a specific plaintext is encrypted under two distinct keys. We introduce an efficient automatic search tool designed to find target-plaintext key collisions....

Recently, the NSA has proposed a block cipher called ARADI and a mode of operation called LLAMA for memory encryption applications. In this note, we comment on this proposal, on its suitability for the intended application, and describe an attack on LLAMA that breaks confidentiality of ciphertext and allows a straightforward forgery attack breaking integrity of ciphertext (INT-CTXT) using a related-IV attack. Both attacks have negligible complexity.

We propose a new wide encryption (WE) mode of operation that satisfies robust authenticated encryption (RAE) and committing security with minimum ciphertext expansion. WE is attracting much attention in the last few years, and its advantage includes RAE security that provides robustness against wide range of misuses, combined with the encode-then-encipher (EtE) construction. Unfortunately, WE-based EtE does not provide good committing security, and there is a recent constant-time CMT-4...

In this note, we introduce the MATTER Tweakable Block Cipher, designed principally for low latency in low-area hardware implementations, but that can also be implemented in an efficient and compact way in software. MATTER is a 512-bit wide balanced Feistel network with three to six rounds, using the ASCON permutation as the round function. The Feistel network defines a keyed, non-tweakable core, which is made tweakable by using the encryption of the tweak as its key. Key and tweak are...

In this paper, we formulate a special class of systems of linear equations over finite fields that appears naturally in the provable security analysis of several MAC and PRF modes of operation. We derive lower bounds on the number of solutions for such systems adhering to some predefined restrictions, and apply these lower bounds to derive tight PRF security for several constructions. We show security up to $2^{3n/4}$ queries for the single-keyed variant of the Double-block Hash-then-Sum...

The collision-resistant hash function is an early cryptographic primitive that finds extensive use in various applications. Remarkably, the Merkle-Damgård and Merkle tree hash structures possess the collision-resistance preserving property, meaning the hash function remains collision-resistant when the underlying compression function is collision-resistant. This raises the intriguing question of whether reducing the number of underlying compression function calls with the...

Software based cryptographic implementations provide flexibility but they face performance limitations. In contrast, hardware based cryptographic accelerators utilize application-specific customization to provide real-time security solutions. Cryptographic instruction-set extensions (CISE) combine the advantages of both hardware and software based solutions to provide higher performance combined with the flexibility of atomic-level cryptographic operations. While CISE is widely used to...

The Ascon specification defines among others an encryption scheme offering authenticated encryption with associated data (AEAD) which is based on a duplex mode of a sponge. With that it is the first of such algorithm selected and about to be standardized by NIST. The sponge size is comparatively small, 320 bits, as expected for lightweight cryptography. With that, the strength of the defined AEAD algorithm is limited to 128 bits. Albeit, the definition of the Ascon AEAD algorithm integrates...

Authenticated Encryption (AE) modes of operation based on Tweakable Block Ciphers (TBC) usually measure efficiency in the number of calls to the underlying primitive per message block. On the one hand, many existing solutions reach a primitive-rate of 1, meaning that each n-bit block of message asymptotically needs a single call to the TBC with output length n. On the other hand, while these modes look optimal in a blackbox setting, they become less attractive when leakage comes into play,...

After NIST’s selection of Dilithium as the primary future standard for quantum-secure digital signatures, increased efforts to understand its implementation security properties are required to enable widespread adoption on embedded devices. Concretely, there are still many open questions regarding the susceptibility of Dilithium to fault attacks. This is especially the case for Dilithium’s randomized (or hedged) signing mode, which, likely due to devastating implementation attacks on the...

The conversion between arithmetic and Boolean masking representations (A2B \& B2A) is a crucial component for side-channel resistant implementations of lattice-based (post-quantum) cryptography. In this paper, we first propose novel $d$-order algorithms for the secure addition (SecADDChain$_q$) and B2A (B2X2A). Our secure adder is well-suited for repeated ('chained') executions, achieved through an improved method for repeated masked modular reduction. The optimized B2X2A gadget removes a...

DCT is a beyond-birthday-bound~(BBB) deterministic authenticated encryption~(DAE) mode proposed by Forler et al. in ACISP 2016, ensuring integrity by redundancy. The instantiation of DCT employs the BRW polynomial, which is more efficient than the usual polynomial in GCM by reducing half of the multiplication operations. However, we show that DCT suffers from a small stretch problem similar to GCM. When the stretch length $\tau$ is small, choosing a special $m$-block message, we can reduce...

Sponge based constructions have gained significant popularity for designing lightweight authenticated encryption modes. Most of the authenticated ciphers following the Sponge paradigm can be viewed as variations of the Transform-then-permute construction. It is known that a construction following the Transform-then-permute paradigm provides security against any adversary having data complexity $D$ and time complexity $T$ as long as $DT \ll 2^{b-r}$. Here, $b$ represents the size of the...

Authenticated encryption is a cryptographic mechanism that allows communicating parties to protect the confidentiality and integrity of message exchanged over a public channel, provided they share a secret key. Some applications require committing authenticated encryption schemes, a security notion that is not covered by the classical requirements of confidentiality and integrity given a secret key. An authenticated encryption (AE) scheme is committing in the strongest sense when it is...

Extremely Lossy Functions (ELFs) are families of functions that, depending on the choice during key generation, either operate in injective mode or instead have only a polynomial image size. The choice of the mode is indistinguishable to an outsider. ELFs were introduced by Zhandry (Crypto 2016) and have been shown to be very useful in replacing random oracles in a number of applications. One open question is to determine the minimal assumption needed to instantiate ELFs. While all...

The National Cyber Security Centre (NCSC) is the government organisation responsible for mitigating cyber security risks to the UK. Our work securing UK public- and private-sector networks involves (amongst many other security measures) research into cryptographic design, primarily to protect data requiring long-term security or data for which we have a particularly low tolerance of risk to its transmission and storage. Our algorithms prioritise robustness over other important...

Web users can gather data from secure endpoints and demonstrate the provenance of sensitive data to any third party by using privacy-preserving TLS oracles. In practice, privacy-preserving TLS oracles remain limited and cannot selectively verify larger sensitive data sets. In this work, we introduce a new oracle protocol, which reaches new scales in selectively verifying the provenance of confidential web data. The novelty of our work is a construction which deploys an honest verifier...

Quantum attacks using superposition queries are known to break many classically secure modes of operation. While these attacks do not necessarily threaten the security of the modes themselves, since they rely on a strong adversary model, they help us to draw limits on the provable security of these modes. Typically these attacks use the structure of the mode (stream cipher, MAC or authenticated encryption scheme) to embed a period-finding problem, which can be solved with a dedicated...

Consider the standard setting of two-party computation where the sender has a secret function $f$ and the receiver has a secret input $x$ and the output $f(x)$ is delivered to the receiver at the end of the protocol. Let us consider the unidirectional message model where only one party speaks in each round. In this setting, Katz and Ostrovsky (Crypto 2004) showed that at least four rounds of interaction between the parties are needed in the plain model (i.e., no trusted setup) if the...

We introduce the QARMAv2 family of tweakable block ciphers. It is a redesign of QARMA (from FSE 2017) to improve its security bounds and allow for longer tweaks, while keeping similar latency and area. The wider tweak input caters to both specific use cases and the design of modes of operation with higher security bounds. This is achieved through new key and tweak schedules, revised S-Box and linear layer choices, and a more comprehensive security analysis. QARMAv2 offers competitive...

We consider the design of a tweakable block cipher from a block cipher whose inputs and outputs are of size $n$ bits. The main goal is to achieve $2^n$ security with a large tweak (i.e., more than $n$ bits). Previously, Mennink at FSE'15 and Wang et al. at Asiacrypt'16 proposed constructions that can achieve $2^n$ security. Yet, these constructions can have a tweak size up to $n$-bit only. As evident from recent research, a tweakable block cipher with a large tweak is generally helpful as a...

In this paper we formally introduce a novel mode of operation based on the cipher block chaining mode. The main idea of this mode is to use a stateful block cipher instead of a stateless one. Afterwards, we show how to implement our proposal and present a performance analysis of our mode. Next, we provide a concrete security analysis by computing a tight bound on the success of adversaries based on their resources. The results of our performance and security analyses are that this novel mode...

While the round function of the AEGIS authenticated encryption algorithms is highly parallelizable, their mode of operation is not. We introduce two new modes to overcome that limitation: AEGIS-128X and AEGIS-256X, that require minimal changes to existing implementations and retain the security properties of AEGIS-128L and AEGIS-256.

OCB3 is a mature and provably secure authenticated encryption mode of operation which allows for associated data (AEAD). This note reports a small flaw in the security proof of OCB3 that may cause a loss of security in practice, even if OCB3 is correctly implemented in a trustworthy and nonce-respecting module. The flaw is present when OCB3 is used with short nonces. It has security implications that are worse than nonce-repetition as confidentiality and authenticity are lost until the key...

We present a new block cipher mode of operation for authenticated encryption (AE), dubbed XOCB, that has the following features: (1) beyond-birthday-bound (BBB) security based on the standard pseudorandom assumption of the internal block cipher if the maximum block length is sufficiently smaller than the birthday bound, (2) rate-1 computation, and (3) supporting any block cipher with any key length. Namely, XOCB has effectively the same efficiency as the seminal OCB while having stronger...

We introduce the Merkle Tree Ladder (MTL) mode of operation for signature schemes. MTL mode signs messages using an underlying signature scheme in such a way that the resulting signatures are condensable: a set of MTL mode signatures can be conveyed from a signer to a verifier in fewer bits than if the MTL mode signatures were sent individually. In MTL mode, the signer sends a shorter condensed signature for each message of interest and occasionally provides a longer reference value that...

The desirable encryption scheme possesses high PRF security, high efficiency, and the ability to produce variable-length outputs. Since designing dedicated secure PRFs is difficult, a series of works was devoted to building optimally secure PRFs from the sum of independent permutations (SoP), Encrypted Davies-Meyer (EDM), its Dual (EDMD), and the Summation-Truncation Hybrid (STH) for variable output lengths, which can be easily instantiated from existing permutations. For increased...

Many modes of operations for block ciphers or tweakable block ciphers do not require invertibility from their underlying primitive. In this work, we study fixed-length Tweakable Pseudorandom Function (TPRF) with large domain extension, a novel primitive that can bring high security and significant performance optimizations in symmetric schemes, such as (authenticated) encryption. Our first contribution is to introduce a new design paradigm, derived from the Iterate-Fork-Iterate...

In our survey of the various zk-EVM constructions, it becomes apparent that verifiable storage of the EVM state starts to be one of the dominating costs. This is not surprising because a big differentiator of EVM from UTXO is exactly the ability to carry states and, most importantly, their transitions; i.e., EVM is a **state** machine. In other words, to build an efficient zk-EVM, one must first build an efficient verifiable state. The common approach, which has been used in...

Confidential Computing is the protection of data in use from access or modification by any unauthorized agent, including privileged software. For example, in Intel SGX (Client and Scalable versions) and TDX, AMD SEV, Arm CCA, and IBM Ultravisor this protection is implemented via access control policies. Some of these architectures also include memory protection schemes relying on cryptography, to protect against physical attacks. We review and classify such schemes, from academia and...

Incompressibility is one of the most fundamental security goals in white-box cryptography. Given recent advances in the design of efficient and incompressible block ciphers such as SPACE, SPNbox and WhiteBlock, we demonstrate the feasibility of reducing incompressible AEAD modes to incompressible block ciphers. We first observe that several existing AEAD modes of operation, including CCM, GCM(-SIV), and OCB, would be all insecure against white-box adversaries even when used with an...

Security against side-channels and faults is a must for the deployment of embedded cryptography. A wide body of research has investigated solutions to secure implementations against these attacks at different abstraction levels. Yet, to a large extent, current solutions focus on one or the other threat. In this paper, we initiate a mode-level study of cryptographic primitives that can ensure security in a (new and practically-motivated) adversarial model combining leakage and faults. Our...

Implementation-based attacks are major concerns for modern cryptography. For symmetric-key cryptography, a significant amount of exploration has taken place in this regard for primitives such as block ciphers. Concerning symmetric-key operating modes, such as Authenticated Encryption with Associated Data (AEAD), the state- of-the-art mainly addresses the passive Side-Channel Attacks (SCA) in the form of leakage resilient cryptography. So far, only a handful of work address Fault Attacks (FA)...

We give characterizations of IND\$-CPA security for a large, natural class of encryption schemes. Specifically, we consider encryption algorithms that invoke a block cipher and otherwise perform linear operations (e.g., XOR and multiplication by fixed field elements) on intermediate values. This class of algorithms corresponds to the Linicrypt model of Carmer & Rosulek (Crypto 2016). Our characterization for this class of encryption schemes is sound but not complete. We then focus on a...

MEGA is a leading cloud storage platform with more than 250 million users and 1000 Petabytes of stored data. MEGA claims to offer user-controlled, end-to-end security. This is achieved by having all data encryption and decryption operations done on MEGA clients, under the control of keys that are only available to those clients. This is intended to protect MEGA users from attacks by MEGA itself, or by adversaries who have taken control of MEGA’s infrastructure. We provide a detailed...

GIFT-COFB is a lightweight AEAD scheme and a submission to the ongoing NIST lightweight cryptography standardization process where it currently competes as a finalist. The construction processes 128-bit blocks with a key and nonce of the same size and has a small register footprint, only requiring a single additional 64-bit register. Be- sides the block cipher, the mode of operation uses a bit permutation and finite field multiplication with different constants. It is a well-known...

Fully Homomorphic Encryption (FHE) is a powerful cryptographic primitive that enables performing computations over encrypted data without having access to the secret key. We introduce OpenFHE, a new open-source FHE software library that incorporates selected design ideas from prior FHE projects, such as PALISADE, HElib, and HEAAN, and includes several new design concepts and ideas. The main new design features can be summarized as follows: (1) we assume from the very beginning that all...

Public-key cryptography, including conventional cryptosystems and post-quantum cryptography, involves computation-intensive workloads. With noticing the extraordinary computing power of AI accelerators, in this paper, we further explore the feasibility to introduce AI accelerators into high-performance cryptographic computing. Since AI accelerators are dedicated to machine learning or neural networks, the biggest challenge is how to transform cryptographic workloads into their operations,...

SHA-3 is considered to be one of the most secure standardized hash functions. It relies on the Keccak-f[1 600] permutation, which operates on an internal state of 1 600 bits, mostly represented as a 5×5×64-bit matrix. While software implementations process the state sequentially in chunks of typically 32 or 64 bits, the Keccak-f[1 600] permutation can benefit a lot from speedup through parallelization. This paper is the first to explore the full potential of parallelization of Keccak-f[1...

Advanced cryptographic protocols such as Zero-knowledge (ZK) proofs of knowledge, widely used in cryptocurrency applications such as Zcash, Monero, Filecoin, Tezos, Topos, demand new cryptographic hash functions that are efficient not only over the binary field $\mathbb{F}_2$, but also over large fields of prime characteristic $\mathbb{F}_p$. This need has been acknowledged by the wider community and new so-called Arithmetization-Oriented (AO) hash functions have been proposed, e.g....

We propose a new AEAD mode of operation for an efficient countermeasure against side-channel attacks. Our mode achieves the smallest memory with high-order masking, by minimizing the states that are duplicated in masking. An $s$-bit key-dependent state is necessary for achieving $s$-bit security, and the conventional schemes always protect the entire $s$ bits with masking. We reduce the protected state size by introducing an unprotected state in the key-dependent state: we protect only a...

The OCB mode of operation for block ciphers has three variants, OCB1, OCB2 and OCB3. OCB1 and OCB3 can be used as secure authenticated encryption schemes whereas OCB2 has been shown to be classically insecure (Inoue et al., Crypto 2019). Even further, in the presence of quantum queries to the encryption functionality, a series of works by Kaplan et al. (Crypto 2016), Bhaumik et al. (Asiacrypt 2021) and Bonnetain et al. (Asiacrypt 2021) have shown how to break the existential unforgeability...

Lightweight cryptography algorithms are increasing in value because they can enhance security under limited resources. National Institute of Standards and Technology is working on standardising lightweight authenticated encryption with associated data. Thirty-two candidates are included in the second round of the NIST selection process, and their specifications differ with respect to various points. Therefore, for each algorithm, the differences in specifications are expected to affect the...

This paper reports new software implementation results for the Skinny-128 tweakable block ciphers on various SIMD architectures. More precisely, we introduce a decomposition of the 8-bit S-box into four 4-bit S-boxes in order to take advantage of vector permute instructions, leading to significant performance improvements over previous constant-time implementations. Since our approach is of particular interest when Skinny-128 is used in sequential modes of operation, we also report how it...

Currently, a vast majority of symmetric-key cryptographic schemes are built as block cipher modes. The block cipher is designed to be hard to distinguish from a random permutation and this is supported by cryptanalysis, while (good) modes can be proven secure if a random permutation takes the place of the block cipher. As such, block ciphers form an abstraction level that marks the border between cryptanalysis and security proofs. In this paper, we investigate a re-factored version of...

In this article the security of the cipher feedback mode of operation with regular external serial re-keying aiming to construct lightweight pseudo-random sequences generator is investigated. For this purpose the new mode of operation called Multi-key CFB, MCFB is introduced, and the estimations of provable security of this new mode in the LOR-CPA model are obtained. Besides that, the counterexample to well-known result of Abdalla-Bellare about security of encryption scheme with...

We fully characterize the post-quantum security of the \(\mathsf{CBC}\), \(\mathsf{CFB}\), \(\mathsf{OFB}\) and \(\mathsf{CTR}\) modes of operation by considering all possible notions of \(\textsf{qIND-qCPA}\) security defined by Carstens, Ebrahimi, Tabia and Unruh (TCC 2021), thus extending the work performed by Anand, Targhi, Tabia and Unruh (PQCrypto 2016). We show that the results obtained by Anand et al. for the \(\textsf{qIND-qCPA-P6}\) security of these modes carry on to the other...

A growing number of lightweight block ciphers are proposed for environments such as the Internet of Things. An important contribution to the reduced implementation cost is a block length n of 64 or 96 bits rather than 128 bits. As a consequence, encryption modes and message authentication code (MAC) algorithms require security beyond the 2^{n/2} birthday bound. This paper provides an extensive treatment of MAC algorithms that offer beyond birthday bound PRF security for both nonce-respecting...

Today's data-intensive applications increasingly suffer from significant performance bottlenecks due to the limited memory bandwidth of the classical von Neumann architecture. Near-Data Processing (NDP) has been proposed to perform computation near memory or data storage to reduce data movement for improving performance and energy consumption. However, the untrusted NDP processing units (PUs) bring in new threats to workloads that are private and sensitive, such as private database queries...

WARP is an energy-efficient lightweight block cipher that is currently the smallest 128-bit block cipher in terms of hardware. It was proposed by Banik et al. in SAC 2020 as a lightweight replacement for AES-128 without changing the mode of operation. This paper proposes key-recovery attacks on WARP based on differential cryptanalysis in single and related-key settings. We searched for differential trails for up to 20 rounds of WARP, with the first 19 having optimal differential...

COMETv1, by Gueron, Jha and Nandi, is a mode of operation for nonce-based authenticated encryption with associated data functionality. It was one of the second round candidates in the ongoing NIST Lightweight Cryptography Standardization Process. In this paper, we study a generalized version of COMETv1, that we call gCOMET, from provable security perspective. First, we present a comprehensive and complete security proof for gCOMET in the ideal cipher model. Second, we view COMET, the...

A large number of the symmetric-key mode of operations, such as classical CBC-MAC, have serial structures. While a serial mode gives an implementation advantage in terms of required memory or footprint compared to the parallel counterparts, it wastes the capability of parallel process even when it is available. The problem is becoming more relevant as lightweight cryptography is going to be deployed in the real world. In this article, we propose an alternative implementation strategy for...

Threshold cryptography enables cryptographic operations while keeping the secret keys distributed at all times. Agrawal et al. (CCS'18) propose a framework for Distributed Symmetric-key Encryption (DiSE). They introduce a new notion of Threshold Symmetric-key Encryption (TSE), in that encryption and decryption are performed by interacting with a threshold number of servers. However, the necessity for interaction on each invocation limits performance when encrypting large datasets, incurring...

A multi-forkcipher (MFC) is a generalization of the forkcipher (FC) primitive introduced by Andreeva et al. at ASIACRYPT'19. An MFC is a tweakable cipher that computes $s$ output blocks for a single input block, with $s$ arbitrary but fixed. We define the MFC security in the ind-prtmfp notion as indistinguishability from $s$ tweaked permutations. Generalizing tweakable block ciphers (TBCs, $s = 1$), as well as forkciphers ($s=2$), MFC lends itself well to building simple-to-analyze modes of...

Secure computation enables two or more parties to jointly evaluate a function without revealing to each other their private input. G-module is an abelian group M, where the group G acts compatibly with the abelian group structure on M. In this work, we present several secure computation protocols for G-module operations in the online/offline mode. We then show how to instantiate those protocols to implement many widely used secure computation primitives in privacy-preserving machine learning...

While server-only authentication with certificates is the most widely used mode of operation for the Transport Layer Security (TLS) protocol on the world wide web, there are many applications where TLS is used in a different way or with different constraints. For example, embedded Internet-of-Things clients may have a server certificate pre-programmed and be highly constrained in terms of communication bandwidth or computation power. As post-quantum algorithms have a wider range of...

Zero-knowledge proofs are highly flexible cryptographic protocols that are an important building block for many secure systems. Typically, these are defined with respect to statements that are formulated as arithmetic operations over a fixed finite field. This inflexibility is a disadvantage when it comes to complex programs, as some fields are more amenable to express certain operations than others. At the same time, there do not seem to be many proofs with a programming model similar to...

GIFT-COFB is a finalist of NIST Lightweight cryptography project that aims at standardizing authenticated encryption schemes for constrained devices. It is a block cipher-based scheme and comes with a provable security result. This paper studies the tightness of the provable security bounds of GIFT-COFB, which roughly tells that, if instantiated by a secure $n$-bit block cipher, we need $2^{n/2}$ encrypted blocks or $2^{n/2}/n$ decryption queries to break the scheme. This paper shows that...

We revisit the classical problem of designing optimally efficient cryptographically secure hash functions. Hash functions are traditionally designed via applying modes of operation on primitives with smaller domains. The results of Shrimpton and Stam (ICALP 2008), Rogaway and Steinberger (CRYPTO 2008), and Mennink and Preneel (CRYPTO 2012) show how to achieve optimally efficient designs of $2n$-to-$n$-bit compression functions from non-compressing primitives with asymptotically optimal...

Advanced Encryption Standard used with Galois Counter Mode, mode of operation is one of the the most secure modes to use the AES. This paper represents an overview of the AES modes focusing the AES-GCM mode and its particularities. Moreover, after a detailed analysis of the possibility of enhancement for the encryption and authentication phase, a method of generating custom encryption schemes based on GF($2^8$) irreducible polynomials different from the standard polynomial used by the...

ForkAE is a NIST lightweight cryptography candidate that uses the forkcipher primitive in two modes of operation -- SAEF and PAEF -- optimized for authenticated encryption of the shortest messages. SAEF is a sequential and online AEAD that minimizes the memory footprint compared to its alternative parallel mode PAEF, catering to the most constrained devices. SAEF was proven AE secure against nonce-respecting adversaries. Due to their more acute and direct exposure to device misuse and...

Boyle et al. (TCC 2019) proposed a new approach for secure computation in the preprocessing model building on function secret sharing (FSS), where a gate $g$ is evaluated using an FSS scheme for the related offset family $g_r(x)=g(x+r)$. They further presented efficient FSS schemes based on any pseudorandom generator (PRG) for the offset families of several useful gates $g$ that arise in "mixed-mode'' secure computation. These include gates for zero test, integer comparison, ReLU, and spline...

Memory encryption with an authentication tree has received significant attentions due to the increasing threats of active attacks and the widespread use of non-volatile memories. It is also gradually deployed to real-world systems, as shown by SGX available in Intel processors. The topic of memory encryption has been recently extensively studied, most actively from the viewpoint of system architecture. In this paper, we study the topic from the viewpoint of provable secure symmetric-key...

We present malleability attacks against encrypted binary executable files when they are encrypted by CBC mode of operation. While the CBC malleability is classic and has been used to attack on various real-world applications, the risk of encrypting binary executable via CBC mode on common OSs has not been widely recognized. We showed that, with a certain non-negligible probability, it is possible to manipulate the CBC-encrypted binary files so that the decryption result allows an arbitrary...

Subterranean 2.0 is a cipher suite that can be used for hashing, authenticated encryption, MAC computation, etc. It was designed by Daemen, Massolino, Mehrdad, and Rotella, and has been selected as a candidate in the second round of NIST's lightweight cryptography standardization process. Subterranean 2.0 is a duplex-based construction and utilizes a single-round permutation in the duplex. It is the simplicity of the round function that makes it an attractive target of cryptanalysis. In...

Unification techniques have been proven to be useful for formal analysis of cryptographic systems. In this paper, we introduce a new unification problem called local XOR unification, motivated by formal analysis of security of modes of operation. The goal in local XOR unification is to find a substitution making two terms equivalent modulo the theory of exclusive-or, but each variable is only allowed to be mapped to a term from a given set of terms. We present two versions of the local XOR...

In an article from HOST 2018, which appears in extended form in the Cryptology ePrint Archive, Baksi, Bhasin, Breier, Khairallah, and Peyrin proposed the tweak-in-plaintext method to protect block ciphers against a differential fault analysis (DFA). We argue that this method lacks existential motivation as neither of its two envisioned use cases, i.e., the electronic codebook (ECB) and the cipher block chaining (CBC) modes of operation, is competitive. Furthermore, in a variant of the method...

PudgyTurtle is a way to use keystream to encode plaintext before XOR-based (stream cipher-like) encryption. It makes stream ciphers less efficient -- a typical implementation requiring about five times as much keystream and producing about twice as much ciphertext -- but also more robust against time-memory-data tradeoff attacks. PudgyTurtle can operate alongside any keystream generator, and thus functions somewhat like an encryption mode for stream ciphers. Here, we introduce the...

In this paper we develop symbolic and computational representations for a class of cryptographic modes of operation, where the symbolic representations are modeled as elements of a term algebra, and we apply them to the analysis of the computational security of the modes. We derive two different conditions on the symbolic representations, a simple one that is sufficient for security, and a more complex one that is both necessary and sufficient, and prove that these properties hold. The...

Hardware obfuscation is widely used in practice to counteract reverse engineering. In recent years, low-level obfuscation via camouflaged gates has been increasingly discussed in the scientific community and industry. In contrast to classical high-level obfuscation, such gates result in recovery of an erroneous netlist. This technology has so far been regarded as a purely defensive tool. We show that low-level obfuscation is in fact a double-edged sword that can also enable stealthy...

In this article, we propose GIFT-COFB, an Authenticated Encryption with Associated Data (AEAD) scheme, based on the GIFT lightweight block cipher and the COFB lightweight AEAD operating mode. We explain how these two primitives can fit together and the various design adjustments possible for performance and security improvements. We show that our design provides excellent performances in all constrained scenarios, hardware or software, while being based on a provably-secure mode and a well...

The bit-sliding paper of Jean et al. (CHES 2017) showed that the smallest-size circuit for SPN based block ciphers such as AES, SKINNY and PRESENT can be achieved via bit-serial implementations. Their technique decreases the bit size of the datapath and naturally leads to a significant loss in latency (as well as the maximum throughput). Their designs complete a single round of the encryption in 168 (resp. 68) clock cycles for 128 (resp. 64) bit blocks. A follow-up work by Banik et al. (FSE...

The selection criteria for NIST's Lightweight Crypto Standardization (LWC) have been slowly shifting towards the lightweight efficiency of designs, given that a large number of candidates already establish their security claims on conservative, well-studied paradigms. The research community has accumulated a decent level of experience on authenticated encryption primitives, thanks mostly to the recently completed CAESAR competition, with the advent of the NIST LWC, the de facto focus is now...

It is known that attackers can exfiltrate data from air-gapped computers through their speakers via sonic and ultrasonic waves. To eliminate the threat of such acoustic covert channels in sensitive systems, audio hardware can be disabled and the use of loudspeakers can be strictly forbidden. Such audio-less systems are considered to be \textit{audio-gapped}, and hence immune to acoustic covert channels. In this paper, we introduce a technique that enable attackers leak data acoustically...

Since Keccak was selected as the SHA-3 standard, both its hash mode and keyed mode have attracted lots of third-party cryptanalysis. Especially in recent years, there is progress in analyzing the collision resistance and preimage resistance of round-reduced Keccak. However, for the preimage attacks on round-reduced Keccak-384/512, we found that the linear relations leaked by the hash value are not well exploited when utilizing the current linear structures. To make full use of the...

The Hill cipher is a classical poly-alphabetical cipher based on matrices. Although known plaintext attacks for the Hill cipher have been known for almost a century, feasible ciphertext only attacks have been developed only about ten years ago and for small matrix dimensions. In this paper we extend the ciphertext only attacks for the Hill cipher in two ways. First, we present two attacks for the affine version of the Hill cipher. Secondly, we show that the presented attacks can be extended...

Spook is one of the 32 candidates that has made it to the second round of the NIST Lightweight Cryptography Standardization process, and is particularly interesting since it proposes differential side channel resistance. In this paper, we present practical distinguishers of the full 6-step version of the underlying permutations of Spook, namely Shadow-512 and Shadow-384, solving challenges proposed by the designers on the permutation. We also propose practical forgeries with 4-step Shadow...

We revisit the security of various generalized Feistel networks. Concretely, for unbalanced, alternating, type-1, type-2, and type-3 Feistel networks built from random functions, we substantially improve the coupling analyzes of Hoang and Rogaway (CRYPTO 2010). For a tweakable blockcipher-based generalized Feistel network proposed by Coron et al. (TCC 2010), we present a coupling analysis and for the first time show that with enough rounds, it achieves 2n-bit security, and this provides...

CONFISCA is the first generic SIMD-based software countermeasure that can concurrently resist against Side-Channel Attack (SCA) and Fault Injection (FI). Its promising strength is presented in a PRESENT cipher case study and compared to software-based Dual-rail with Pre-charge Logic concurrent countermeasure. It has lower overhead, wider usability, and higher protection. Its protection has been compared using Correlation Power Analysis, Welch’s T-Test, Signal- to- Noise Ratio and Normalized...

Triggered by the increasing deployment of embedded cryptographic devices (e.g., for the IoT), the design of authentication, encryption and authenticated encryption schemes enabling improved security against side-channel attacks has become an important research direction. Over the last decade, a number of modes of operation have been proposed and analyzed under different abstractions. In this paper, we investigate the practical consequences of these findings. For this purpose, we first...

The sponge duplex is a popular mode of operation for constructing authenticated encryption schemes. In fact, one can assess the popularity of this mode from the fact that around $ 25 $ out of the $ 56 $ round 1 submissions to the ongoing NIST lightweight cryptography (LwC) standardization process are based on this mode. Among these, $14$ sponge-type constructions are selected for the second round consisting of $32$ submissions. In this paper, we generalize the duplexing interface of the...

In 2008, Drimer et al. proposed different AES implementations on a Xilinx Virtex-5 FPGA, making efficient use of the DSP slices and BRAM tiles available on the device. Inspired by their work, in this paper, we evaluate the feasibility of extending AES with the popular GCM mode of operation, still concentrating on the optimal use of DSP slices and BRAM tiles. We make use of a Xilinx Zynq UltraScale+ MPSoC FPGA with improved DSP features. For the AES part, we implement Drimer’s round-based and...

Proactive security is the notion of defending a distributed system against an attacker who compromises different devices through its lifetime, but no more than a threshold number of them at any given time. The emergence of threshold wallets for more secure cryptocurrency custody warrants an efficient proactivization protocol tailored to this setting. While many proactivization protocols have been devised and studied in the literature, none of them have communication patterns ideal for...

We present distinguishing attacks (based on the Birthday Paradox) which show that the use of $2^{\ell}$ permutations for a block cipher is insufficient to obtain a security of $\ell$ bits in the Ideal Cipher Model. The context is that of an Oracle that can provide an Adversary the ciphertexts of a very small number of known plaintexts under a large number of (session) keys and IVs/nonces. Our attacks distinguish an ideal cipher from a ``perfectly ideal'' block cipher, realised as an Oracle...

Memory fault attacks, inducing errors in computations, have been an ever-evolving threat to cryptographic schemes since their discovery for cryptography by Boneh et al. (Eurocrypt 1997). Initially requiring physical tampering with hardware, the software-based rowhammer attack put forward by Kim et al. (ISCA 2014) enabled fault attacks also through malicious software running on the same host machine. This led to concerning novel attack vectors, for example on deterministic signature schemes,...

We propose SPAE, a single pass, patent free, authenticated encryption with associated data (AEAD) for AES. The algorithm has been developped to address the needs of a growing trend in IoT systems: storing code and data on a low cost flash memory external to the main SOC. Existing AEAD algorithms such as OCB, GCM, CCM, EAX , SIV, provide the required functionality however in practice each of them suffer from various drawbacks for this particular use case. Academic contributions such as ASCON...

In this article, we propose two new families of very lightweight and efficient authenticated encryption with associated data (AEAD) modes, Romulus and Remus, that provide security beyond the birthday bound with respect to the block-length $n$. The former uses a tweakable block cipher (TBC) as internal primitive and can be proven secure in the standard model. The later uses a block cipher (BC) as internal primitive and can be proven secure in the ideal cipher model. Both our modes allow to...

XTS is an encryption scheme for storage devices standardized by IEEE and NIST. It is based on Rogaway's XEX tweakable block cipher and is known to be secure up to the collisions between the blocks, thus up to around $2^{n/2}$ blocks for $n$-bit blocks. However this only implies that the theoretical indistinguishability notion is broken with $O(2^{n/2})$ queries and does not tell the practical risk against the plaintext recovery if XTS is targeted. We show several plaintext recovery attacks...

Kerberos is one of the earliest network security protocols, providing authentication between clients and servers with the assistance of trusted servers. It remains widely used, notably as the default authentication protocol in Microsoft Active Directory (thus shipped with every major operating system), and is the ancestor of modern single sign-on protocols like OAuth and OpenID Connect. There have been many analyses of Kerberos in the symbolic (Dolev--Yao) model, which is more amenable to...

Authenticated encryption (AE) has been a vital operation in cryptography due to its ability to provide confidentiality, integrity, and authenticity at the same time. Its use has soared in parallel with widespread use of the Internet and has led to several new schemes. There have been studies investigating software performance of various schemes. However, the same is yet to be done for hardware. We present a comprehensive survey of hardware (specifically ASIC) performance of the most commonly...