[continued from previous message]

The CRYSTALS-Dilithium digital signature scheme, selected by NIST as a post-quantum cryptography (PQC) standard under the name ML-DSA, employs a public key compression technique intended for performance optimization. Specifically, the module learning
with error instance $({\bf A}, {\bf t})$ is compressed by omitting the low-order bits ${\bf t_0}$ of the vector ${\bf t}$. It was recently shown that knowledge of ${\bf t_0}$ enables more effective side-channel attacks on Dilithium implementations.
Another recent work demonstrated a method for reconstructing ${\bf t_0}$ from multiple signatures. In this paper, we build on this method by applying profiled deep learning-assisted side-channel analysis to partially recover the least significant bit of $
{\bf t_0}$ from power traces. As a result, the number of signatures required for the reconstruction of ${\bf t_0}$ can be reduced by roughly half. We demonstrate how the new ${\bf t_0}$ reconstruction method enhances the efficiency of recovering the
secret key component ${\bf s}_1$, and thus facilitates digital signature forgery, on an ARM Cortex-M4 implementation of Dilithium.



## 2024/2047

* Title: Breaking and Provably Restoring Authentication: A Formal Analysis of SPDM 1.2 including Cross-Protocol Attacks
* Authors: Cas Cremers, Alexander Dax, Aurora Naska
* [Permalink](https://eprint.iacr.org/2024/2047)
* [Download](https://eprint.iacr.org/2024/2047.pdf)

### Abstract

The SPDM (Security Protocol and Data Model) protocol is a standard under development by the DMTF consortium, and supported by major industry players including Broadcom, Cisco, Dell, Google, HP, IBM, Intel, and NVIDIA. SPDM 1.2 is a complex protocol that
aims to provide platform security, for example for communicating hardware components or cloud computing scenarios.
In this work, we provide the first holistic, formal analysis of SPDM 1.2: we model the full protocol flow of SPDM considering all of its modes ΓÇô especially the complex interaction between its different key-exchange modes ΓÇô in the framework of the
Tamarin prover, making our resulting model one of the most complex Tamarin models to date. To our surprise, Tamarin finds a cross-protocol attack that allows a network attacker to completely break authentication of the pre-shared key mode. We implemented
our attack on the SPDM reference implementation, and reported the issue to the SPDM developers. DMTF registered our attack as a CVE with CVSS rating 9 (critical).
We propose a fix and develop the first formal symbolic proof using the Tamarin prover for the fixed SPDM 1.2 protocol as a whole. The resulting model of the main modes and their interactions is highly complex, and we develop supporting lemmas to enable
proving properties in the Tamarin prover, including the absence of all cross-protocol attacks. Our fix has been incorporated into both the reference implementation and the newest version of the standard. Our results highlight the need for a holistic
analysis of other internet standards and the importance of providing generalized security guarantees across entire protocols.



## 2024/2048

* Title: How to Compress Garbled Circuit Input Labels, Efficiently
* Authors: Marian Dietz, Hanjun Li, Huijia Lin
* [Permalink](https://eprint.iacr.org/2024/2048)
* [Download](https://eprint.iacr.org/2024/2048.pdf)

### Abstract

Garbled Circuits are essential building blocks in cryptography, and extensive research has explored their construction from both applied and theoretical perspectives. However, a challenge persists: While theoretically designed garbled circuits offer
optimal succinctness--remaining constant in size regardless of the underlying circuitΓÇÖs complexit--and are reusable for multiple evaluations, their concrete computational costs are prohibitively high. On the other hand, practically efficient garbled
circuits, inspired by YaoΓÇÖs garbled circuits, encounter limitations due to substantial communication bottlenecks and a lack of reusability.

To strike a balance, we propose a novel concept: online-offline garbling. This approach leverages instance-independent and (partially) reusable preprocessing during an offline phase, to enable the creation of constant-size garbled circuits in an online
phase, while maintaining practical efficiency. Specifically, during the offline stage, the garbler generates and transmits a reference string, independent of the computation to be performed later. Subsequently, in the online stage, the garbler
efficiently transforms a circuit into a constant-size garbled circuit. The evaluation process relies on both the reference string and the garbled circuit.

We demonstrate that by leveraging existing tools such as those introduced by Applebaum et al. (CryptoΓÇÖ13) and Chongwon et al. (CryptoΓÇÖ17), online-offline garbling can be achieved under a variety of assumptions, including the hardness of Learning With
Errors (LWE), Computational Diffie-Hellman (CDH), and factoring. In contrast, without the help of an offline phase, constant-size garbling is only feasible under the LWE and circular security assumptions, or the existence of indistinguishability
obfuscation. However, these schemes are still very inefficient, several orders of magnitude more costly than Yao-style garbled circuits.

To address this, we propose a new online-offline garbling scheme based on Ring LWE. Our scheme offers both asymptotic and concrete efficiency. It serves as a practical alternative to Yao-style garbled circuits, especially in scenarios where online
communication is constrained. Furthermore, we estimate the concrete latency using our approach in realistic settings and demonstrate that it is 2-20X faster than using Yao-style garbled circuits. This improvement is estimated without taking into account
parallelization of computation, which can lead to further performance improvement using our scheme.



## 2024/2049

* Title: BBB Secure Arbitrary Length Tweak TBC from n-bit Block Ciphers
* Authors: Arghya Bhattacharjee, Ritam Bhaumik, Nilanjan Datta, Avijit Dutta, Sougata Mandal
* [Permalink](https://eprint.iacr.org/2024/2049)
* [Download](https://eprint.iacr.org/2024/2049.pdf)

### Abstract

At FSE'15, Mennink introduced two tweakable block ciphers, $\widetilde{F}[1]$ and $\widetilde{F}[2]$, both utilizing an $n$-bit tweak. It was demonstrated that $\widetilde{F}[1]$ is secure for up to $2^{2n/3}$ queries, while $\widetilde{F}[2]$ is secure
for up to $2^n$ queries, assuming the underlying block cipher is an ideal cipher with $n$-bit key and $n$-bit data. Later, at ASIACRYPT'16, Wang et al. showed a birthday bound attack on Mennink's design (which was later corrected in the eprint version {\
textbf eprint 2015/363}) and proposed 32 new candidates for tweakable block ciphers that are derived from $n$-bit ideal block ciphers. It was shown that all the $32$ constructions are provably secure up to $2^n$ queries. All the proposed designs by both
Mennink and Wang et al. admit only $n$-bit tweaks. In FSE'23, Shen and Standaert proposed a tweakable block cipher, $\widetilde{G2}$, which uses $2n$-bit tweaks and is constructed from three $n$-bit block cipher calls, proving its security up to $n$ bits,
assuming that the underlying block cipher is an ideal cipher. They have also shown that it is impossible to design a tweakable block cipher with $2n$-bit tweaks using only two $n$-bit block cipher calls while achieving security beyond the birthday bound.
In this paper, we advance this research further. We show that any tweakable block cipher design with $3n$-bit tweaks based on only three block cipher calls, where at least one key is tweak-independent, is vulnerable to a birthday bound distinguishing
attack. We then propose a tweakable block cipher, $\widetilde{\textsf{G}_3}^*$ that uses three block cipher calls and admits $3n$-bit tweaks, achieves security up to $O(2^{2n/3})$ queries when all three block cipher keys are tweak-dependent. Furthermore,
we prove that using four ideal block cipher calls, with at least one key being tweak-dependent, is necessary and sufficient to achieve $n$-bit security for a tweakable block cipher that admits $3n$-bit tweaks. Finally, we propose a tweakable block cipher,
$\widetilde{\textsf{G}_r}$, which uses $(r+1)$ block cipher calls and processes $rn$-bit tweaks, achieving security up to $O(2^n)$ queries when at least one block cipher key is tweak-dependent.



## 2024/2050

* Title: Simulation Secure Multi-Input Quadratic Functional Encryption: Applications to Differential Privacy
* Authors: Ferran Alborch Escobar, Sébastien Canard, Fabien Laguillaumie
* [Permalink](https://eprint.iacr.org/2024/2050)
* [Download](https://eprint.iacr.org/2024/2050.pdf)

### Abstract

Multi-input functional encryption is a primitive that allows for the evaluation of an $\ell$-ary function over multiple ciphertexts, without learning any information about the underlying plaintexts. This type of computation is useful in many cases where
one has to compute over encrypted data, such as privacy-preserving cloud services, federated learning, or more generally delegation of computation from multiple clients. It has recently been shown by Alborch et al. in PETS '24 to be useful to construct a
randomized functional encryption scheme for obtaining differentially private data analysis over an encrypted database supporting linear queries.

In this work we propose the first secret-key multi-input quadratic functional encryption scheme satisfying simulation security. Current constructions supporting quadratic functionalities, proposed by Agrawal et al. in CRYPTO '21 and TCC '22, only reach
indistinguishibility-based security. Our proposed construction is generic, and for a concrete instantiation, we propose a new function-hiding inner-product functional encryption scheme proven simulation secure against one challenge ciphertext in the
standard model, which is of independent interest. We then use these two results to construct an efficient randomized quadratic functional encryption scheme, from which we obtain differentially private data analysis over an encrypted database supporting
quadratic queries. Finally, we give and fully benchmark an implementation of the randomized scheme. This work is an extended version of the paper "Simulation Secure Multi-Input Quadratic Functional Encryption" at SAC '24, where the multi-input quadratic
functional encryption scheme and function-hiding inner-product functional encryption schemes were first presented (Section 3 and Seciton 4).



## 2024/2051

* Title: Simple Power Analysis assisted Chosen Cipher-Text Attack on ML-KEM
* Authors: Alexandre Berzati, Andersson Calle Viera, Maya Chartouny, David Vigilant
* [Permalink](https://eprint.iacr.org/2024/2051)
* [Download](https://eprint.iacr.org/2024/2051.pdf)

### Abstract

Recent work proposed by Bernstein et al. (from EPRINT 2024) identified two timing attacks, KyberSlash1 and KyberSlash2, targeting ML-KEM decryption and encryption algorithms, respectively, enabling efficient recovery of secret keys. To mitigate these
vulnerabilities, correctives were promptly applied across implementations. In this paper, we demonstrate a very simple side-channel-assisted power analysis attack on the patched implementations of ML-KEM. Our result showed that original timing leakage
can be shifted to power consumption leakage that can be exploited on specific data. We performed a practical validation of this attack on both the standard and a shuffled implementations of ML-KEM on a Cortex-M4 platform, confirming its effectiveness.
Our approach enables the recovery of the ML-KEM secret key in just 30 seconds for the standard implementation, and approximately 3 hours for the shuffled implementation, achieving a 100% success rate in both cases.



## 2024/2052

* Title: Improved Rejection Sampling for Compact Lattice Signatures
* Authors: Joel Gärtner
* [Permalink](https://eprint.iacr.org/2024/2052)
* [Download](https://eprint.iacr.org/2024/2052.pdf)

### Abstract

One of the primary approaches used to construct lattice-based signature schemes is through the ΓÇ£Fiat-Shamir with abortsΓÇ¥ methodology. Such a scheme may abort and restart during signing which corresponds to rejection sampling produced signatures to
ensure that they follow a distribution that is independent of the secret key. This rejection sampling is only feasible when the output distribution is sufficiently wide, limiting how compact this type of signature schemes can be.

In this work, we develop a new method to construct signatures influenced by the rejection condition. This allows our rejection sampling to target significantly narrower output distributions than previous approaches, allowing much more compact signatures.
The combined size of a signature and a verification key for the resulting scheme is less than half of that for ML-DSA and comparable to that of compact hash-and-sign lattice signature schemes, such as Falcon.



## 2024/2053

* Title: Optimally Secure TBC Based Accordion Mode
* Authors: Nilanjan Datta, Avijit Dutta, Shibam Ghosh, Hrithik Nandi
* [Permalink](https://eprint.iacr.org/2024/2053)
* [Download](https://eprint.iacr.org/2024/2053.pdf)

### Abstract

The design of tweakable wide block ciphers has advanced significantly over the past two decades. This evolution began with the approach of designing a wide block cipher by Naor and Reingold. Since then, numerous tweakable wide block ciphers have been
proposed, many of which build on existing block ciphers and are secure up to the birthday bound for the total number of blocks queried. Although there has been a slowdown in the development of tweakable wide block cipher modes in last couple of years,
the latest NIST proposal for accordion modes has reignited interest and momentum in the design and analysis of these ciphers. Although new designs have emerged, their security often falls short of optimal (i.e., $n$-bit) security, where $n$ is the output
size of the primitive. In this direction, designing an efficient tweakable wide block cipher with $n$-bit security seems to be an interesting research problem. An optimally secure tweakable wide block cipher mode can easily be turned into a misuse-
resistant RUP secure authenticated encryption scheme with optimal security. This paper proposes $\textsf{HCTR+}$, which turns an $n$-bit tweakable block cipher (TBC) with $n$-bit tweak into a variable input length tweakable block cipher. Unlike tweakable
$\textsf{HCTR}$, $\textsf{HCTR+}$ ensures $n$-bit security regardless of tweak repetitions. We also propose two TBC-based almost-xor-universal hash functions, named $\textsf{PHASH+}$ and $\textsf{ZHASH+}$, and use them as the underlying hash functions in
the $\textsf{HCTR+}$ construction to create two TBC-based $n$-bit secure tweakable wide block cipher modes, $\textsf{PHCTR+}$ and $\textsf{ZHCTR+}$. Experimental results show that both $\textsf{PHCTR+}$ and $\textsf{ZHCTR+}$ exhibit excellent software
performance when their underlying TBC is instantiated with $\textsf{Deoxys-BC-128-128}$.



## 2024/2054

* Title: Greedy Algorithm for Representative Sets: Applications to IVLBC and GIFT-64 in Impossible Differential Attack
* Authors: Manjeet Kaur, Tarun Yadav, Manoj Kumar, Dhananjoy Dey
* [Permalink](https://eprint.iacr.org/2024/2054)
* [Download](https://eprint.iacr.org/2024/2054.pdf)

### Abstract

The impossible differential (ID) attack is crucial for analyzing the strength of block ciphers. The critical aspect of this technique is to identify IDs, and the researchers introduced several methods to detect them. Recently, the researchers extended
the mixed-integer linear programming (MILP) approach by partitioning the input and output differences to identify IDs. The researchers proposed techniques to determine the representative set and partition table of a set over any nonlinear function. In
this paper, we introduce a deterministic algorithm using the greedy approach~\cite{cormen2022introduction} for finding the representative set and partition table of a set over any nonlinear function. This algorithm iteratively selects the set that covers
the maximum uncovered elements of the target set. This performs better than the existing algorithms in terms of time complexity. We use this algorithm to compute the representative sets and partition tables of the two block ciphers, IVLBC and GIFT-64,
and identify 6-round IDs for them. Our research contributes a deterministic algorithm to compute the representative set and partition table of a set over any nonlinear function with at most 16-bit input size.



## 2024/2055

* Title: Zeroed Out: Cryptanalysis of Weak PRFs in Alternating Moduli
* Authors: Irati Manterola Ayala, Håvard Raddum
* [Permalink](https://eprint.iacr.org/2024/2055)
* [Download](https://eprint.iacr.org/2024/2055.pdf)

### Abstract

The growing adoption of secure multi-party computation (MPC) has driven the development of efficient symmetric key primitives tailored for MPC. Recent advancements, such as the alternating moduli paradigm, have shown promise but leave room for
cryptographic and practical improvements. In this paper, we analyze a family of weak pseudorandom functions (wPRF) proposed at Crypto 2024, focusing on the One-to-One parameter sets. We demonstrate that these configurations fail to achieve their intended
one-to-one mappings and exploit this observation to develop an efficient key recovery attack. The attacks reveal significant vulnerabilities, reducing the complexity of key recovery to O(2^(╬╗/2) log_2 (╬╗)) for the Standard One-to-One wPRF and O(2^(0.84╬
╗)) for the Reversed Moduli variantΓÇô both substantially below their claimed ╬╗-bit security. We validate our findings through experimental evaluations, confirming alignment between predicted and observed attack complexities.



## 2024/2056

* Title: Exact Template Attacks with Spectral Computation
* Authors: Meriem Mahar, Mammar Ouladj, Sylvain Guilley, Hacène Belbachir, Farid Mokrane
* [Permalink](https://eprint.iacr.org/2024/2056)
* [Download](https://eprint.iacr.org/2024/2056.pdf)

### Abstract

The so-called Gaussian template attacks (TA) is one of the optimal Side-Channel Analyses (SCA) when the measurements are captured with normal noise.
In the SCA literature, several optimizations of its implementation are introduced, such as coalescence and spectral computation. The coalescence consists of averaging traces corresponding to the same plaintext value, thereby coalescing (synonymous:
compacting) the dataset. Spectral computation consists of sharing the computational workload when estimating likelihood across key hypotheses.

State-of-the-art coalescence leverages the Law of Large Numbers (LLN) to compute the mean of equivalent traces.
This approach comes with a drawback because the LLN is just an asymptotic approximation.
So it does not lead to an exact Template Attack, especially for a few number of traces.
In this paper, we introduce a way of calculating the TA exactly and with the same computational complexity (using the spectral approach), without using the LLN, regardless of the number of messages.

For the experimental validation of this approach, we use the ANSSI SCA Database (ASCAD), with different numbers of messages and different amounts of samples per trace.
Recall that this dataset concerns a software implementation of AES-128 bits, running on an ATMEGA-8515 microprocessor.



## 2024/2057

* Title: Leveraging remote attestation APIs for secure image sharing in messaging apps
* Authors: Joel Samper, Bernardo Ferreira
* [Permalink](https://eprint.iacr.org/2024/2057)
* [Download](https://eprint.iacr.org/2024/2057.pdf)

### Abstract

Sensitive pictures such as passport photos and nudes are commonly shared through mobile chat applications. One popular strategy for the privacy protection of this material is to use ephemeral messaging features, such as the view once snaps in Snapchat.
However, design limitations and implementation bugs in messaging apps may allow attackers to bypass the restrictions imposed by those features on the received material. One way by which attackers may accomplish so is by tampering with the software stack
on their own devices. In this paper, we propose and test a protection strategy based on a multiplatform system that encrypts and decrypts sensitive pictures on top of messaging apps and performs remote attestation with available app integrity APIs to
safeguard its security. Our analysis and experiments show that, compared to previous proposals for image encryption in a middleware, remote attestation offers increased security, adds privacy benefits, simplifies integration, and improves usability by
not requiring users to exchange key material a priori. In our experiments, it incurs an added average latency of 3.8 and 4.5 seconds when sending and receiving private pictures, respectively.



## 2024/2058

* Title: Learning with Errors from Nonassociative Algebras
* Authors: Andrew Mendelsohn, Cong Ling
* [Permalink](https://eprint.iacr.org/2024/2058)
* [Download](https://eprint.iacr.org/2024/2058.pdf)

### Abstract

We construct a provably-secure structured variant of Learning with Errors (LWE) using nonassociative cyclic division algebras, assuming the hardness of worst-case structured lattice problems, for which we are able to give a full search-to-decision
reduction, improving upon the construction of Grover et al. named `Cyclic Learning with Errors' (CLWE). We are thus able to create structured LWE over cyclic algebras without any restriction on the size of secret spaces, which was required for CLWE as a
result of its restricted security proof. We reduce the shortest independent vectors problem in ideal lattices, obtained from ideals in orders of such algebras, to the decision variant of LWE defined for nonassociative CDAs. We believe this variant has
greater security and greater freedom with parameter choices than CLWE, and greater asymptotic efficiency of multiplication than module LWE. Our reduction requires new results in the ideal theory of such nonassociative algebras, which may be of
independent interest. We then adapt an LPR-like PKE scheme to hold for nonassociative spaces, and discuss the efficiency and security of our construction, showing that it is immune to certain subfield attacks. Finally, we give example parameters to
construct algebras for cryptographic use.



## 2024/2059

* Title: Minimizing the Use of the Honest Majority in YOSO MPC with Guaranteed Output Delivery
* Authors: Rishabh Bhadauria, James Hsin-yu Chiang, Divya Ravi, Jure Sternad, Sophia Yakoubov
* [Permalink](https://eprint.iacr.org/2024/2059)
* [Download](https://eprint.iacr.org/2024/2059.pdf)

### Abstract

Cleve (STOC 86) shows that an honest majority is necessary for MPC with guaranteed output delivery. In this paper, we show that while an honest majority is indeed necessary, its involvement can be minimal. We demonstrate an MPC protocol with guaranteed
output delivery, the majority of which is executed by a sequence of committees with dishonest majority; we leverage one committee with an honest majority, each member of which does work independent of the circuit size. Our protocol has the desirable
property that every participant speaks only once (YOSO, Crypto 2021).
As a building block of independent interest, we introduce public computation, which is essentially privacy-free MPC with guaranteed output delivery (akin to smart contracts realized on blockchains). We instantiate public computation on a public bulletin
board in three different ways (with different assumption / round / space utilization trade-offs).



## 2024/2060

* Title: "These results must be false": A usability evaluation of constant-time analysis tools
* Authors: Marcel Fourné, Daniel De Almeida Braga, Jan Jancar, Mohamed Sabt, Peter Schwabe, Gilles Barthe, Pierre-Alain Fouque, Yasemin Acar
* [Permalink](https://eprint.iacr.org/2024/2060)
* [Download](https://eprint.iacr.org/2024/2060.pdf)

### Abstract

Cryptography secures our online interactions, transactions, and trust. To achieve this goal, not only do the cryptographic primitives and protocols need to be secure in theory, they also need to be securely implemented by cryptographic library developers
in practice.

However, implementing cryptographic algorithms securely is challenging, even for skilled professionals, which can lead to vulnerable implementations, especially to side-channel attacks. For timing attacks, a severe class of side-channel attacks, there
exist a multitude of tools that are supposed to help cryptographic library developers assess whether their code is vulnerable to timing attacks. Previous work has established that despite an interest in writing constant-time code, cryptographic library
developers do not routinely use these tools due to their general lack of usability. However, the precise factors affecting the usability of these tools remain unexplored. While many of the tools are developed in an academic context, we believe that it is
worth exploring the factors that contribute to or hinder their effective use by cryptographic library developers.

To assess what contributes to and detracts from usability of tools that verify constant-timeness (CT), we conducted a two-part usability study with 24 (post) graduate student participants on 6 tools across diverse tasks that approximate real-world use
cases for cryptographic library developers.

We find that all studied tools are affected by similar usability issues to varying degrees, with no tool excelling in usability, and usability issues preventing their effective use.

Based on our results, we recommend that effective tools for verifying CT need usable documentation, simple installation, easy to adapt examples, clear output corresponding to CT violations, and minimal noninvasive code markup. We contribute first steps
to achieving these with limited academic resources, with our documentation, examples, and installation scripts.

--- SoupGate-Win32 v1.05
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