Property-Preserving Hash (PPH) achieves compression of large-scale data while providing predicate evaluation functionality on hash digests. PPH can be used to construct new cryptographic primitives or directly applied to privacy-sensitive data scenarios. These constructions or applications impose privacy requirements on the information leakage of PPH. The property definition of PPH follows the Direct-Access Robustness. However, the information leakage of PPH hash values concerning the preimage has not been formally analyzed or defined. In this work, we first propose ℒ -Simulation, a simulation-based definition to formalize the information disclosure of PPH hash values with respect to the preimage. We introduce a leakage profile in the simulation to quantify the level of preimage leakage. Subsequently, based on this formal definition, we analyze and evaluate the PPH scheme in Order-Revealing Encryption (ORE) and all PPH schemes for the Hamming distance predicate. Our formal proofs demonstrate that the PPH in ORE achieves an ideal leakage bound. However, the PPH schemes by Fleischhacker and Simkin at Eurocrypt 2021 and Fleischhacker et al. at Eurocrypt 2022 suffer from partial preimage leakage. To address this issue, we propose a new PPH construction for the Hamming distance predicate. Our scheme reduces leakage while supporting additive homomorphism and scalar multiplicative homomorphism, enhancing security and broadening its applicability.

Side-channel attacks pose a significant threat to cryptographic implementations by exploiting physical information to infer secret keys. Trace segmentation, which involves identifying key-related operations within complete side-channel traces, is a necessary prerequisite for side-channel attacks. Existing trace segmentation methods exhibit several limitations, including reliance on human expertise, inability to address random delay countermeasures, and excessive overhead. In this paper, we propose TS-Seg, a side-channel trace segmentation method based on temporal-spatial feature fusion. TS-Seg extracts temporal and spatial features from side-channel traces by employing a novel model architecture and loss function, thereby enabling automated and accurate trace segmentation. We evaluate TS-Seg on three post-quantum cryptographic algorithms (NTRU, Saber, and Kyber) implemented on an ARM Cortex-M4 embedded processor, achieving a segmentation accuracy of 100

TLS 1.3 is at the heart of secure modern internet communications. With the rise of quantum attacks, post-quantum TLS 1.3, built on post-quantum key encapsulation mechanisms (KEMs), has naturally become a major research focus. At Eurocrypt 2022, Huguenin-Dumittan and Vaudenay demonstrated that KEMs secure against chosen-plaintext attacks (CPA) are sufficient to construct a secure TLS 1.3 handshake in the random oracle model (ROM), but their security reduction incurs an 𝒪(q^6) loss, where q is the number of random oracle queries. Improving their security bounds was left as an open problem. To address this problem, Zhou et al. took the first step at Asiacrypt 2024, improving the loss factor to 𝒪(q^2) in the ROM and 𝒪(q^4) in the quantum ROM (QROM) for OW-CPA secure KEMs, and to 𝒪(q) (ROM) and 𝒪(q^2) (QROM) for IND-CPA secure KEMs. In this work, we advance the state-of-the-art by providing tighter security reductions for TLS 1.3 handshake based on CPA-secure KEMs. We introduce a new security notion, IND-1CCA-1MAC, and show that with a slight ciphertext expansion, the reduction losses can be significantly improved to 𝒪(q) (ROM) and 𝒪(q^2) (QROM) for OW-CPA secure KEMs, and to only 𝒪(1) in both models for IND-CPA secure KEMs. Moreover, we prove that without additional modifications such as ciphertext expansion, the loss of 𝒪(q) (ROM) and 𝒪(q^2) (QROM) is unavoidable. Finally, we analyze the security of TLS 1.3 from CPA-secure KEMs in the hybrid key exchange setting, and provide experimental evidence that ciphertext expansion is a practical trade-off for mitigating reduction losses.

The widespread adoption of network security protocols has led to an increasing demand for the inspection of encrypted traffic. Most existing solutions that provide authorized inspectors with visibility of encrypted traffic are designed for the Transport Layer Security (TLS) protocol, and the best-known is the solution involving key escrow with the inspector. The Secure Shell (SSH) protocol has a similar architecture to TLS and is frequently used to secure access to remote systems, but SSH traffic inspection is less well-explored. In fact, the existing approach to TLS inspection can also be adapted to SSH. However, IA2-TLS, the state-of-the-art solution for TLS, is vulnerable to security risks because the inspection key is used in a symmetric way. Inspired by these observations, we propose a new variant of SSH called Inspectable SSH (iSSH). iSSH retains the core idea of IA2-TLS, but overcomes its limitations by using an asymmetric inspection key pair. Moreover, iSSH is compatible with standard SSH and provides flexible deployment options. Finally, we expanded upon the standard SSH security model and rigorously proved the security of key exchange in iSSH.

TLS 1.3 is a crucial protocol for securing modern internet communications. To facilitate a smooth transition to post-quantum security, hybrid key exchange, which combines classical key exchange algorithms with post-quantum key encapsulation mechanisms (KEMs), is proposed to enhance the security of the current TLS 1.3 handshake. However, existing drafts and implementations of hybrid key exchange for TLS 1.3 primarily rely on CCA-secure KEMs (i.e., secure against chosen-ciphertext attacks) based on the Fujisaki-Okamoto (FO) transform. The re-encryption step in their decapsulation algorithms not only introduces additional performance overhead but also raises the risk of side-channel attacks. Although Huguenin-Dumittan and Vaudenay (Eurocrypt 2022) and Zhou et al. (Asiacrypt 2024) demonstrated that the weaker CPA-secure KEMs (i.e., secure against chosen-plaintext attacks) suffice for constructing a secure TLS 1.3 handshake, their analyses were limited to single-KEM settings and did not consider the hybrid key exchange scenario. This work challenges the necessity of CCA security by proving that CPA-secure KEMs are sufficient for the TLS 1.3 handshake even in the hybrid key exchange setting. We provide the first formal security proofs for this claim, covering both the classical random oracle model (ROM) and the quantum random oracle model (QROM), thereby ensuring security against quantum adversaries. To validate the practical benefits, we conduct an extensive performance evaluation based on the latest OpenSSL implementation. Our results show that using CPA-secure KEMs yields up to 44.8% performance improvement at the key exchange layer and up to approximately 9% acceleration for the full TLS 1.3 handshake. Beyond performance gains, this approach reduces the codebase's attack surface by eliminating the re-encryption step, thereby mitigating a class of side-channel vulnerabilities. Our work positions CPA-secure KEMs as a secure, efficient, and practical alternative for standardizing and deploying post-quantum TLS 1.3 even with hybrid key exchange.

The field of Password-Authenticated Key Exchange (PAKE) protocols has been actively explored for more than three decades, and it was not until 2020 that the IRTF working group CFRG selected the CPace protocol as the recommended PAKE standard. The Universally Composable (UC) security of CPace has been comprehensively studied by Abdalla et al. (ASIACRYPT'21). However, typical UC models do not capture cryptographic subversion attacks which could manipulate the cryptographic implementations to leak some secret covertly. To achieve subversion-resilience in UC models, Chakraborty et al. (EUROCRYPT'22) and Arnold et al. (Eprint 2023/1951) both extended reverse firewalls (Mironov and Stephens-Davidowitz, EUROCRYPT'15) to the UC setting with different considerations. In this work, we propose a subversion-resilient PAKE protocol, called srCPace, that UC-realizes a lazy-extraction PAKE functionality under subversion corruption. Note that current models (both Chakraborty et al.'s model and Arnold et al.'s) assume the existence of authenticated channels while PAKE protocols typically run on unauthenticated channels. To close the gap, we revisit the main theorem of Arnold et al. in the setting of unauthenticated communication. Then, we modify the CPace protocol to support particular reverse firewalls. Finally, by equipping the modified CPace with reverse firewalls, we obtain srCPace and prove its UC security with subversion-resilience by applying our adapted theorem. Our protocol enhances the security of CPace when deployed in the real world where implementations might be corrupted.

Authenticated key exchange (AKE) protocol is an essential tool for secure communication in practice. To defend against subversion attacks that compromise the security of cryptosystem by subverting the implementation of algorithms, Dodis et al. (CRYPTO’16) introduced the first subversion-resilient AKE protocol utilizing the reverse firewalls (RFs) by Mironov and Stephens-Davidowitz (EUROCRYPT’15), and proved its security within a non-standard model. In this paper, we propose a generic subversion-resilient AKE construction under the classic game-based AKE model. Compared to Dodis et al. ’s model, our model is more strict and captures the standard multi-challenge and “single-bit-guess” security, which requires all the test keys to be real-or-random. Our AKE construction follows the standard “ 1×+2× ” paradigm for designing AKE protocols, with the key encapsulation mechanism (KEM) providing some specific properties like malleability and universal decryptability. The security of our AKE construction is tightly based on the security of the underlying KEM and the underlying signature scheme. We instantiate our construction using the plain Diffie-Hellman key encapsulation, resulting in a protocol that is tightly secure based on the strong Diffie-Hellman assumption. Finally, using the strong twin Diffie-Hellman technique of Cash et al. (EUROCRYPT’08), we obtain an AKE protocol with reverse firewalls that achieves tight security based on the standard computational Diffie-Hellman assumption.

Subversion-resilient cryptography has garnered increasing attention in recent years due to growing concerns about cryptographic subversions in real-world applications. Among the existing countermeasures, the notion of cryptographic reverse firewalls (RFs), initially proposed by Mironov and Stephens-Davidowitz (EUROCRYPT 2015) and later extended by Chakraborty et al. (EUROCRYPT 2022) to the universally composable (UC) model, has proven to be a powerful tool for building subversion-resilient cryptographic protocols. In this work, we focus on designing subversion-resilient authenticated key exchange (AKE) protocols, which are critical components of secure Internet communication. We present the first generic framework for subversion-resilient UC-secure AKE protocols leveraging RFs. Inspired by the state-of-the-art advancements by Chakraborty et al. (ASIACRYPT 2024), we address subversions: where a party’s implementation is covertly altered to exfiltrate secrets or behave unpredictably when triggered by adversarial inputs. A key contribution of our work is the introduction of a new AKE functionality which, for the first time, incorporates security against key control, an essential aspect of achieving subversion resilience. We also provide a concrete instantiation of our framework, demonstrating its feasibility in practice. Notably, the RFs in our proposed AKE protocol are transparent, an important property of RF as defined originally, which allows deployment of RF without all parties explicitly knowing about it and allows robust security. Achieving transparency for RFs has been widely regarded as challenging, particularly when addressing broader subversion attacks (e.g., input-trigger attacks) in the UC model. Our approach, thus, not only advances the state of AKE protocol design, but also offers insights into building other subversion-resilient protocols in the UC model using transparent RFs.

We propose a threat detection framework that enhances provenance-based APT analysis by combining event clustering with LLM-driven threat pattern extraction refinement. Our method is designed to work in conjunction with existing systems like Kairos, which able to detect anomaly time windows. We first group fine-grained events into semantic clusters to preserve behavioral context, then apply structured threat patterns to identify suspicious sequences. To improve precision, we introduce a two-stage refinement: relaxing matching constraints for high recall, followed by LLM-driven filtering to assess semantic plausibility in framework of MITRE based on "Part Chain of Pattern" assumption. Evaluated on CADETS E3 and THEIA E3 using defender-observable ground truth, our approach outperforms Kairos in precision and F1-score. The results show that integrating structured pattern matching with contextual language models can effectively enhance existing detection pipelines, offering a practical path toward more accurate and interpretable threat hunting.

TLS 1.3 is widely used to realize secure communication over the Internet. Existing security analyses of TLS 1.3 primarily focus on its handshake protocol which is indeed an authenticated key exchange (AKE) protocol, and implicitly neglect the so-called subversion attacks (e.g., breaking TLS via Dual EC) in the real world. Reverse firewall (RF) is a prevalent approach to defend against subversion attack. To the best of our knowledge, the only two subversion-resilient AKE protocols with RFs are proposed by Dodis et al. (CRYPTO'16) and Bossuat et al. (ESORICS'20). The security of both protocols is proved under game-based model which is insufficient for the concurrent execution of multiple TLS instances in practice. In this paper, we propose $\mathsf {srTLS}$ , a variant of the TLS 1.3 full one round-trip time (1-RTT) handshake protocol with RFs under the universally composable (UC) model. In particular, we first present the ideal functionality of unilateral AKE $\mathcal {F}_{\mathsf {uaKE}}$ . Then, we use RFs with outer transparency to circumvent the difficulty in sanitizing the messages of handshake protocol, and prove that $\mathsf {srTLS}$ UC-realizes $\mathcal {F}_{\mathsf {uaKE}}$ in the presence of subversion attacks. Finally, we integrate $\mathsf {srTLS}$ and existing subversion-resilient AKE protocols into TLS 1.3. The evaluation result demonstrates that $\mathsf {srTLS}$ achieves at least a 44.86% efficiency improvement over other subversion-resilient AKE protocols.

Motivated by Edward Snowden's revelations, Bellare et al. introduced the notion of Algorithm Substitution Attacks (ASAs) at CRY-PTO'14. ASAs mainly consider adversaries who could manipulate cryptographic algorithms to leak secret information. Since then, ASAs have been extensively studied against various cryptographic primitives and protocols. This work investigates ASAs on Asymmetric (Group) Message Franking (A(G)MF) which is used for tracing illegal messages over end-to-end encrypted communication channels. We introduce the ASA model for A(G)MF, highlighting the potential for attackers to leak the sender's secret key and partial randomness of signature by substituting franking algorithm. We then propose two ASAs against Tyagi et al.'s AMF scheme (CRYPTO'19): an asymmetric attack requiring two consecutive signatures for key recovery, and a symmetric attack requiring only one signature for leaking the whole secret key. We extend these attacks to Lai et al.'s AGMF scheme (EUROCRYPT'23). Finally, we discuss some potential countermeasures to strengthen A(G)MF against such threats. Our findings underscore the potential threat of ASAs on A(G)MF, emphasizing the necessity for continued development of subversion-resistant message franking, particularly in the asymmetric setting.

The SM9 identity-based encryption (IBE) scheme is a cryptographic standard used in China, and has been incorporated into the ISO/IEC standard in 2021. This work primarily proposes a countermeasure to secure the SM9 IBE scheme if its implementation is tampered with or deviated from the standard specification. Such attacks, known as subversion attacks, are feasible and powerful in real-world cryptographic application scenarios. Our goal is to design a subversion-resilient variant of the SM9 IBE scheme, primarily using the cryptographic reverse firewall (CRF) proposed by Mironov and Stephens-Davidowitz at EUROCRYPT 2015. A CRF can sanitize cryptographic transcripts to eliminate covert channels, necessitating that the underlying primitive be rerandomizable. Unfortunately, the rerandomizability of the SM9 IBE scheme is disabled for ensuring security against chosen ciphertext attack (CCA). Hence, we shift our focus to a relaxed version of CCA security called RCCA security, offering security guarantees comparable to CCA security while allowing for ciphertext rerandomization. For this purpose, we design an efficient and RCCA-secure variant of the SM9 IBE scheme with provable security that can integrate with CRFs to achieve subversion resilience.

Ensuring both security and efficiency in Nearest Neighbor Search (NNS) on large datasets remains a formidable challenge, as it often leads to substantial computation and communication costs due to the resource-intensive nature of ciphertext computations. To date, there have been some solutions that are capable of handling privacy-preserving NNS queries on big datasets. However, these approaches either impose significant communication and computational burdens or compromise security. In this paper, we introduce a novel framework, namely SecureANNS, for secure approximate nearest neighbor search in the semi-honest setting. Our approach begins by enhancing the building blocks of secure NNS, specifically the multiplexer and comparison operations, through oblivious transfer. We then adapt the plaintext Locality-Sensitive Hashing algorithm to select a smaller subset, reducing the need for extensive two-party computation. Finally, we introduce a new bucket retrieval algorithm for efficient subset retrieval. Experimental results on various datasets demonstrate that our SecureANNS achieves a speedup of 4 × and 14 × compared to two state-of-the-art methods respectively.