International Association
for Cryptologic Research

A long-standing question in the blockchain community is which class of computations are efficiently expressible in cryptocurrencies with limited scripting languages, such as Bitcoin Script. Such languages expose a reduced trusted computing base, thereby being less prone to hacks and vulnerabilities, but have long been believed to support only limited classes of payments.

In this work, we confute this long-standing belief by showing for the first time that arbitrary computations can be encoded in today's Bitcoin Script, without introducing any language modification or additional security assumptions, such as trusted hardware, trusted parties, or committees with secure majority. In particular, we present $\mathsf{BitVM}$, a two-party protocol realizing a generic virtual machine by a combination of cryptographic and incentive mechanisms. We conduct a formal analysis of $\mathsf{BitVM}$, characterizing its functionality, system assumptions, and security properties. We further demonstrate the practicality of our approach: in the optimistic case (i.e., in the absence of disputes between parties), our protocol requires just three on-chain transactions, whereas in the pessimistic case, the number of transactions grows logarithmically with the size of the virtual machine. This work not only solves a long-standing theoretical problem, but it also promises a strong practical impact, enabling the development of complex applications in Bitcoin.

In this paper we define the novel concept token-based key exchange (TBKE), which can be considered a cross between non-interactive key exchange (NIKE) and attribute-based encryption (ABE). TBKE is a scheme that allows users within an organization to generate shared keys for a subgroup of users through the use of personal tokens and secret key. The shared key generation is performed locally and no interaction between users or with a server is needed.

The personal tokens are derived from a set of universal tokens and a master secret key which are generated and stored on a trusted central server. Users are only required to interact with the server during setup or if new tokens are provided. To reduce key escrow issues the server can be erased after all users have received their secret keys. Alternatively, if the server is kept available TBKE can additionally provide token revocation, addition and update. We propose a very simple TBKE protocol using bilinear pairings. The protocol is secure against user coalitions based upon a novel hidden matrix problem. The problems requires an adversary to compute where the adversary must compute a matrix product in the exponent, where some components are given in the clear and others are hidden as unknown exponents. We argue that the hidden matrix problem is as hard as dLog in the bilinear group model.

In this paper, we present a batching technique for oracles corresponding to codewords of a Reed–Solomon code. This protocol is inspired by the round function of the STIR protocol (CRYPTO 2024). Using this oracle batching protocol, we propose a construction of a practically efficient accumulation scheme, which we call BOIL. Our accumulation scheme can be initiated with an arbitrary correlated holographic IOP, leading to a new class of PCD constructions. The results of this paper were originally given as a presentation at zkSummit12.

This paper studies quantum linear key-recovery attacks on block ciphers. The first such attacks were last-rounds attacks proposed by Kaplan et al. (ToSC 2016), which combine a linear distinguisher with a guess of a partial key. However, the most efficient classical attacks use the framework proposed by Collard et al. (ICISC 2007), which computes experimental correlations using the Fast Walsh-Hadamard Transform. Recently, Schrottenloher (CRYPTO 2023) proposed a quantum version of this technique, in which one uses the available data to create a quantum \emph{correlation state}, which is a superposition of subkey candidates where the amplitudes are the corresponding correlations. A limitation is that the good subkey is not marked in this state, and cannot be found easily.

In this paper, we combine the correlation state with another distinguisher. From here, we can use Amplitude Amplification to recover the right key. We apply this idea to Feistel ciphers and exemplify different attack strategies on LOKI91 before applying our idea on the CAST-128 and CAST-256 ciphers. We demonstrate the approach with two kinds of distinguishers, quantum distinguishers based on Simon's algorithm and linear distinguishers. The resulting attacks outperform the previous Grover-meet-Simon attacks.

This work proposes a multi-level compiler framework to transform programs with loop structures to efficient algorithms over fully homomorphic encryption (FHE). We observe that, when loops operate over ciphertexts, it becomes extremely challenging to effectively interpret the control structures within the loop and construct operator cost models for the main body of the loop. Consequently, most existing compiler frameworks have inadequate support for programs involving non-trivial loops, undermining the expressiveness of programming over FHE. To achieve both efficient and general program execution over FHE, we propose CHLOE, a new compiler framework with multi-level control-flow analysis for the effective optimization of compound repetition control structures. We observe that loops over FHE can be classified into two categories depending on whether the loop condition is encrypted, namely, the transparent loops and the oblivious loops. For transparent loops, we can directly inspect the control structures and build operator cost models to apply FHE-specific loop segmentation and vectorization in a fine-grained manner. Meanwhile, for oblivious loops, we derive closed-form expressions and static analysis techniques to reduce the number of potential loop paths and conditional branches. In the experiment, we show that \NAME can compile programs with complex loop structures into efficient executable codes over FHE, where the performance improvement ranges from $1.5\times$ to $54\times$ (up to $10^{5}\times$ for programs containing oblivious loops) when compared to programs produced by the-state-of-the-art FHE compilers.

We propose a solution for optimized scaling of multi-party computation using the MP-SPDZ framework (CCS’20). It does not use manual optimization but extends the compiler and the virtual machine of the framework, thus providing an improvement for any user. We found that our solution improves timings four-fold for a simple example in MP-SPDZ, and it improves an order of magnitude on every framework using secret sharing considered by Hastings et al. (S&P’19) either in terms of time or RAM usage. The core of our approach is finding a balance between communication round optimization and memory usage.

Oblivious pseudorandom function (OPRF) is a two-party cryptographic protocol that allows the receiver to input $x$ and learn $F(x)$ for some PRF $F$, only known to the sender. For private set intersection (PSI) applications, OPRF protocols have evolved to enhance efficiency, primarily using symmetric key cryptography. Current state-of-the-art protocols, such as those by Rindal and Schoppmann (Eurocrypt '21), leverage vector oblivious linear evaluation (VOLE) and oblivious key-value store (OKVS) constructions.

In this work, we identify a flaw in an existing security proof, and present practical attacks in the malicious model, which results in additional PRF evaluations than the previous works' claim. In particular, the attack for malicious model is related to the concept of OKVS overfitting, whose hardness is conjectured in previous works. Our attack is the first one to discuss the concrete hardness of OKVS overfitting problem.

As another flavour of contribution, we generalize OKVS-based OPRF constructions, suggesting new instantiations using a VOLE protocol with only Minicrypt assumptions. Our generalized construction shows improved performance in high-speed network environments, narrowing the efficiency gap between the OPRF constructions over Cryptomania and Minicrypt.

We present a garbling scheme for Boolean circuits with 1 bit per gate communication based on either ring learning with errors (RLWE) or NTRU assumption, with key-dependent message security. The garbling consists of 1) a homomorphically encrypted seed that can be expanded to encryption of many pseudo-random bits and 2) one-bit stitching information per gate to reconstruct garbled tables from the expanded ciphertexts. By using low-complexity PRGs, both the garbling and evaluation of each gate require only O(1) homomorphic addition/multiplication operations without bootstrapping.

In this study, we present the first side-channel attack on the ARADI block cipher, exposing its vulnerabilities to physical attacks in non-profiled scenarios. We propose a novel bitwise divide-and-conquer methodology tailored for ARADI, enabling key recovery. Furthermore, based on our attack approach, we present a stepwise method for recovering the full 256-bit master key. Through experiments on power consumption traces from an ARM processor, we demonstrate successful recovery of target key bits, validating the effectiveness of our proposed method. Our findings highlight critical weaknesses in physical security of ARADI and underscore the necessity of implementing effective countermeasures to address side-channel vulnerabilities.

As advancements in quantum computing present potential threats to current cryptographic systems, it is necessary to reconsider and adapt existing cryptographic frameworks. Among these, Grover's algorithm reduces the attack complexity of symmetric-key encryption, making it crucial to evaluate the security strength of traditional symmetric-key systems. In this paper, we implement an efficient quantum circuit for the ARIA symmetric-key encryption and estimate the required quantum resources. Our approach achieves a reduction of over 61\% in full depth and over 65.5\% in qubit usage compared to the most optimized previous research. Additionally, we estimate the cost of a Grover attack on ARIA and evaluate its post-quantum security strength.

This article generalizes the widely-used GLV decomposition for scalar multiplication to a broader range of elliptic curves with moderate CM discriminant \( D < 0 \) (up to a few thousand in absolute value). Previously, it was commonly believed that this technique could only be applied efficiently for small \( D \) values (e.g., up to \( 100 \)). In practice, curves with \( j \)-invariant \( 0 \) are most frequently employed, as they have the smallest possible \( D = -3 \). This article participates in the decade-long development of numerous real-world curves with moderate \( D \) in the context of ZK-SNARKs. Such curves are typically derived from others, which limits the ability to generate them while controlling the magnitude of \( D \). The most notable example is so-called "lollipop" curves demanded, among others, in the Mina protocol.

Additionally, the new results are relevant to one of the "classical" curves (with \( D = -619 \)) from the Russian ECC standard. This curve was likely found using the CM method (with overwhelming probability), though this is not explicitly stated in the standard. Its developers seemingly sought to avoid curves with small \( D \) values, aiming to mitigate potential DLP attacks on such curves, and hoped these attacks would not extend effectively to \( D = -619 \). One goal of the present article is to address the perceived disparity between the \( D = -3 \) curves and the Russian curve. Specifically, the Russian curve should either be excluded from the standard for potential security reasons or local software should begin leveraging the advantages of the GLV decomposition.

This work investigates constructions of threshold fully homomorphic encryption with low communication, i.e., with small ciphertexts and small decryption shares. In this context, we discuss in detail the technicalities for achieving full-fledged threshold FHE, and put forward limitations regarding prior works, including an attack against the recent construction of Boudgoust and Scholl [ASIACRYPT 2023]. In light of our observations, we generalize the definition of threshold fully homomorphic encryption by adding an algorithm which allows to introduce additional randomness in ciphertexts before they are decrypted by parties. In this setting, we are able to propose a construction which offers small ciphertexts and small decryption shares.

As dataset sizes continue to grow, users face increasing difficulties in performing processing tasks on their local machines. From this, privacy concerns about data leakage have led data owners to upload encrypted data and utilize secure range queries to cloud servers. To address these challenges, order-revealing encryption (ORE) has emerged as a promising solution for large numerical datasets. Building on this, delegatable order-revealing encryption (DORE) was introduced, allowing operations between encrypted datasets with different secret keys in multi-client ORE environments. DORE operates through authorization tokens issued by the data owner. However, security concerns had arisen about unauthorized users exploiting data without permission, leading to the development of a secure order-revealing encryption scheme (SEDORE). These attacks can result in unauthorized data access and significant financial losses in modern cloud service providers (CSPs) utilizing pay-per-query systems. In addition, efficient delegatable order-revealing encryption (EDORE), which improves speed and storage compared to SEDORE with identical security levels, was also introduced. Although both SEDORE and EDORE were designed to be robust against these attacks, we have identified that they still retain the same vulnerabilities within the same threat model. To address these issues, we propose Verifiable Delegatable Order-Revealing Encryption (VDORE), which protects against attacks by using the Schnorr Signature Scheme to verify the validity of the token that users send. We propose a precise definition and robust proof to improve the unclear definition and insufficient proof regarding token unforgeability in the SEDORE. Furthermore, the token generation algorithm in VDORE provides about a $1.5\times$ speed-up compared to SEDORE.

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) attack on the proposed LED cipher, estimating the quantum resources required for the corresponding attack oracles. The STO attack outperforms the usual Grover's search when the state size is less than the key size. Beyond analyzing the cipher itself (i.e., the ECB mode), this work also evaluates the effectiveness of quantum attacks on LED across different modes of operation.

With the emergence of DeFi, attacks based on re-ordering transactions have become an essential problem for public blockchains. Such attacks include front-running or sandwiching transactions, where the adversary places transactions at a particular place within a block to influence a financial asset’s market price. In the Ethereum space, the value extracted by such attacks is often referred to as miner/maximal extractable value (MEV), which to date is estimated to have reached a value of more than USD 1.3B. A promising approach to protect against MEV is to hide the transaction data so block proposers cannot choose the order in which transactions are executed based on the transactions’ content. This paper describes the cryptographic protocol underlying the Shutter network. Shutter has been available as an open-source project since the end of 2021 and has been running in production since Oct. 2022.

A message authentication code (MAC) is a symmetric-key cryptographic function used to authenticate a message by assigning it a tag. This tag is a short string that is difficult to reproduce without knowing the key. The tag ensures both the authenticity and integrity of the message, enabling the detection of any modifications.

A significant number of existing message authentication codes (MACs) are based on block ciphers (BCs) and tweakable block ciphers (TBCs). These MACs offer various trade-offs in properties, such as data processing rate per primitive call, use of single or multiple keys, security levels, pre- or post-processing, parallelizability, state size, and optimization for short/long queries.

In this work, we propose the $\mathsf{Sonikku}$ family of expanding primitive based MACs, consisting of three instances: $\mathsf{BabySonic}$, $\mathsf{DarkSonic}$, and $\mathsf{SuperSonic}$. The $\mathsf{Sonikku}$ MACs are -- 1) faster than the state-of-the-art TBC-based MACs; 2) secure beyond the birthday bound in the input block size; 3) smaller in state size compared to state-of-the-art MACs; and 4) optimized with diverse trade-offs such as pre/post-processing-free execution, parallelization, small footprint, and suitability for both short and long queries. These attributes make them favorable for common applications as well as ``IoT'' and embedded devices where processing power is limited.

On a Cortex-M4 32-bit microcontroller, $\mathsf{BabySonic}$ with $\mathsf{ForkSkinny}$ achieves a speed-up of at least 2.11x (up to 4.36x) compared to state-of-the-art ZMAC with $\mathsf{SKINNY}$ for 128-bit block sizes and queries of 95B or smaller. $\mathsf{DarkSonic}$ and $\mathsf{SuperSonic}$ with $\mathsf{ForkSkinny}$ achieve a speed-up of at least 1.93x for small queries of 95B or smaller and 1.48x for large queries up to 64KB, respectively, against ZMAC with $\mathsf{SKINNY}$ for both 64- and 128-bit block sizes.

Similar to ZMAC and PMAC2x, we then demonstrate the potential of our MAC family by using $\mathsf{SuperSonic}$ to construct a highly efficient, beyond-birthday secure, stateless, and deterministic authenticated encryption scheme, which we call SonicAE.

Evaluating the security of LWE-based KEMs involves two crucial metrics: the hardness of the underlying LWE problem and resistance to decryption failure attacks, both significantly influenced by the secret key and error distributions. To mitigate the complexity and timing vulnerabilities of Gaussian sampling, modern LWE-based schemes often adopt either the uniform or centered binomial distribution (CBD).

This work focuses on Kyber to evaluate its security under both distributions. Compared with the CBD, the uniform distribution over the same range enhances the LWE hardness but also increases the decryption failure probability, amplifying the risk of decryption failure attacks. We introduce a majority-voting-based key recovery method, and carry out a practical decryption failure attack on Kyber512 in this scenario with a complexity of $2^{37}$.

Building on this analysis, we propose uKyber, a variant of Kyber that employs the uniform distribution and parameter adjustments under the asymmetric module-LWE assumption. Compared with Kyber, uKyber maintains comparable hardness and decryption failure probability while reducing ciphertext sizes. Furthermore, we propose a multi-value sampling technique to enhance the efficiency of rejection sampling under the uniform distribution. These properties make uKyber a practical and efficient alternative to Kyber for a wide range of cryptographic applications.

The rise of microarchitectural attacks has necessitated robust detection and mitigation strategies to secure computing systems. Traditional tools, such as static and dynamic code analyzers and attack detectors, often fall short due to their reliance on predefined patterns and heuristics that lack the flexibility to adapt to new or evolving attack vectors. In this paper, we introduce for the first time a microarchitecture security assistant, built on OpenAI's GPT-3.5, which we refer to as µLAM. This assistant surpasses conventional tools by not only identifying vulnerable code segments but also providing context-aware mitigations, tailored to specific system specifications and existing security measures. Additionally, µLAM leverages real-time data from dynamic Hardware Performance Counters (HPCs) and system specifications to detect ongoing attacks, offering a level of adaptability and responsiveness that static and dynamic analyzers cannot match.

For fine-tuning µLAM, we utilize a comprehensive dataset that includes system configurations, mitigations already in place for different generations of systems, dynamic HPC values, and both vulnerable and non-vulnerable source codes. This rich dataset enables µLAM to harness its advanced LLM natural language processing capabilities to understand and interpret complex code patterns and system behaviors, learning continuously from new data to improve its predictive accuracy and respond effectively in real time to both known and novel threats, making it an indispensable tool against microarchitectural threats. In this paper, we demonstrate the capabilities of µLAM by fine-tuning and testing it on code utilizing well-known cryptographic libraries such as OpenSSL, Libgcrypt, and NaCl, thereby illustrating its effectiveness in securing critical and complex software environments.

Proxy re-encryption (PRE) allows semi-honest party (called proxy) to convert a ciphertext under a public key into a ciphertext under another public key. Due to this functionality, there are various applications such as encrypted email forwarding, key escrow, and securing distributed file systems. Meanwhile, post-quantum cryptography (PQC) is one of the most important research areas because development of quantum computers has been advanced recently. In particular, there are many researches on public key encryption (PKE) algorithms selected/submitted in the NIST (National Institute of Standards and Technology) PQC standardization. However, there is no post-quantum PRE scheme secure against adaptive chosen ciphertext attacks (denoted by CCA security) while many (post-quantum) PRE schemes have been proposed so far. In this paper, we propose a bounded CCA secure PRE scheme based on CRYSTALS-Kyber which is a selected algorithm in the NIST PQC competition. To this end, we present generic constructions of bounded CCA secure PRE. Our generic constructions start from PRE secure against chosen plaintext attacks (denoted by CPA security). In order to instantiate our generic constructions, we present a CPA secure PRE scheme based on CRYSTALS-Kyber.

The proliferation of data outsourcing and cloud services has heightened privacy vulnerabilities. CKKS, among the most prominent homomorphic encryption schemes, allows computations on encrypted data, serving as a critical privacy safeguard. However, performance remains a central bottleneck, hindering widespread adoption. Existing optimization efforts often prioritize latency reduction over throughput performance. This paper presents HI-CKKS, a throughput-oriented High-performance Implementation of CKKS homomorphic encryption, addressing these challenges. Our HI-CKKS introduces a batch-supporting asynchronous execution scheme, effectively mitigating frequent data interactions and high waiting delays between hosts and servers in service-oriented scenarios. We analyze the fundamental (I)NTT primitive, which is critical in CKKS, and develop a hierarchical, hybrid high-throughput implementation. This includes efficient arithmetic module instruction set implementations, unified kernel fusion, and hybrid memory optimization strategies that significantly improve memory access efficiency and the performance of (I)NTT operations. Additionally, we propose a multi-dimensional parallel homomorphic multiplication scheme aimed at maximizing throughput and enhancing the performance of (I)NTT and homomorphic multiplication. In conclusion, our implementation is deployed on the RTX 4090, where we conduct a thorough throughput performance evaluation of HI-CKKS, enabling us to pinpoint the most effective parallel parameter settings. Compared to the CPU implementation, our system achieves throughput increases of $175.08\times$, $191.27\times$, and $679.57\times$ for NTT, INTT, and HMult, respectively. And our throughput performance still demonstrates a significant improvement, ranging from $1.54\times$ to $693.17\times$ compared to the latest GPU-based works.