Communication protocol is a fundamental component of modern networking. With proliferation of networking and communication, users have become more concerned about privacy. This leads to development of end-to-end encrypted messaging systems which provides confidential communication. Besides confidentiality, there is an increasing demand for additional security properties such as unforgeability, anonymity, off-the-record (OTR), and consistency. However, efficiently achieving these properties simultaneously, especially on resource-constrained mobile devices, remains a significant challenge. In this paper, we propose MERIT, a novel multi-designated receiver authenticated broadcast encryption scheme that satisfies all the above security guarantees in a highly efficient manner. MERIT ensures the following key properties: (i) unforgeability prevents unauthorized parties from generating valid messages; (ii) privacy safeguards the messages and identities of the sender and receivers from non-designated parties; (iii) OTR ensures that receivers cannot later prove the origin of the messages even with their secret keys; and (iv) consistency ensures that all designated receivers obtain identical decrypted messages and identities. The core building block of MERIT is a practical multi-designated verifier signature (PMDVS), which might be of independent interest. We employed a novel batched cut-and-choose technology to prove that the ciphertext is well-formed. This results in an order-of-magnitude efficiency improvement in our scheme compared to its counterparts that rely on general-purpose zero-knowledge proofs. We then show how MERIT leverages PMDVS to provide unforgeability, privacy, OTR, and consistency in the scenario of group messaging. We provide security analysis to demonstrate that MERIT satisfies these security guarantees. We also conduct a thorough performance implementation, and the experimental results demonstrate that MERIT is highly efficient for deployment on mobile devices.
Quasi-adaptive non-interactive zero-knowledge (QA-NIZK) arguments are fundamental cryptographic primitives widely used in privacy-preserving technologies such as anonymous credentials, group signatures, e-cash, and blockchain-based applications. We present the first tightly secure unbounded simulation sound quasi-adaptive non-interactive zero-knowledge argument system from simple assumptions. The construction has a security loss ofO(1), a compact common reference string, constant size proofs, and its security relies on the hardness of the well-known SXDH assumption. Our result improves state-of-the-art (Couteau and Hartmann, CRYPTO 2020) in terms of the proof size (about three times), a lower security loss, and also with respect to the underlying hardness assumptions. The tight security reduction enables shorter key-length recommendations, leading to improved concrete efficiency. Our main technical contribution is a novel proof technique inspired by the randomization technique of the Naor-Yung double-encryption paradigm and the adaptive partitioning due to Hofheinz (EUROCRYPT 2017).
Discreet Log Contracts (DLCs) enable conditional Bitcoin payments using external oracles, but their efficiency depends on cryptography, system design, and oracle interac- tion. This thesis introduces a lightweight, modular Rust framework for prototyping and benchmarking DLC components, with parsing, computation, storage, and oracle inter- faces separated. We implement optimizations for anticipation point computation, parallel processing, and Schnorr adaptor signatures, while outlining theoretical improvements. In collaboration with the community, we integrate a performant Schnorr adaptor and pro- vide, to our knowledge, the first direct comparison of Schnorr- and ECDSA-based adaptor signatures. Benchmarks show Schnorr pre-signing up to five times faster than ECDSA, with further gains from parallelism and basis optimization, demonstrating how careful design improves the practicality of DLCs for advanced Bitcoin contracts.
Ashutosh Kumar, Manik Malhotra, A. Anjali, Amrendra Singh Yadav
Vehicular Ad Hoc Networks (VANETs) require ultra-low-latency authentication in high-mobility scenarios, decentralized trust, and emerging post-quantum security threats. This paper proposes a lightweight blockchain-assisted group authentication framework that integrates post-quantum cryptography with decentralized trust management. The scheme leverages CRYSTALS-Kyber for secure group key distribution, CRYSTALS-Dilithium for message authentication, and zero-knowledge proofs to achieve conditional anonymity and unlinkability. A permissioned Hyperledger Besu blockchain logs encrypted group keys and dynamically updated roadside unit reputation scores, enabling scalable and accountable authentication without monetary transaction overhead. Formal security analysis under the Dolev–Yao adversary model demonstrates confidentiality, authentication, replay resistance, and unlinkability based on standard post-quantum assumptions. Performance evaluation using OMNeT++ and SUMO shows up to 52.7% reduction in communication overhead and a group key update latency of 1.2 ms in dense traffic scenarios, while maintaining high throughput and effective Sybil attack detection. These results highlight the practicality of the proposed framework for post-quantum secure VANET authentication.
Card-based zero-knowledge proof (ZKP) protocols allow a prover to convince a verifier that it knows a witness of a given statement, without revealing any information, using a physical deck of playing cards. Previous studies have focused on puzzles with a specific connected component, such as a simple cycle and a polyomino. In this study, we propose a unified approach to handle a family of connected components, including a tree, path, cycle, and polyomino. This approach achieves this verification in O(mn) steps relative to a given grid size m × n. Using this approach, we construct a card-based ZKP protocol for Nurimeizu, where the goal is to find the shortest path on a given grid.
This paper analyzes the shortcomings of traditional authentication mechanisms in web applications operating over the secure TLS 1.3 protocol. It is established that even with an encrypted channel, the transmission of secret data (passwords, tokens) remains a primary attack vector. An improved protocol is proposed that integrates an authentication mechanism based on zero-knowledge proofs (zk-SNARK) immediately after session establishment via Elliptic Curve Diffie-Hellman (ECDHE) key exchange. This approach completely eliminates the transmission of client credentials, significantly increasing resistance to phishing and server database compromises.
Seema C K, Sharan V Talwar, subhash Chandra K R Patel, S. E. R. Sacha Emile R.
The Internet of Things (IoT) presents critical security challenges including device identity spoofing, replay attacks, and data tampering across billions of deployed endpoints. This work presents ZK-IoTChain, a blockchain-enabled security framework that integrates zk-SNARK-based device authentication with Merkle-anchored data integrity in a unified architecture. The proposed system employs a three-layer design consisting of device-side proof generation, on-chain Groth16 verification, and IPFS-based off-chain storage. This architecture ensures privacy-preserving authentication while maintaining scalability and cost efficiency. Experimental evaluation on the Ethereum Sepolia testnet demonstrates a mean proof generation latency of 3.21 seconds and on-chain verification latency of approximately 125 milliseconds, with an average gas cost of 278,400 per authentication. The framework achieves a 99.98% reduction in storage cost compared to full on-chain approaches. Security analysis under the Dolev–Yao adversary model confirms effective mitigation of identity spoofing, replay attacks, data tampering, and man-in-the-middle (MITM) attacks. The results highlight ZK-IoTChain as a practical and efficient solution for secure, scalable, and privacy-preserving IoT ecosystems.
We introduce behavior-bound signatures (BBS), a signature framework in which each signature attests not only to signer authenticity but also to the satisfaction of a prescribed behavioral policy. Unlike traditional digital signatures—whose acceptance is determined by identity validity alone—BBS enforces compliance at the level of the verification predicate: a signature is accepted if and only if a zero-knowledge proof establishes that a residual function value δ(x)=∣ϕ(x)−τ∣\delta(x)=|\phi(x)-\tau|δ(x)=∣ϕ(x)−τ∣ lies below a threshold ε\varepsilonε. Thus, compliance safety is reduced to zero-knowledge soundness rather than to external monitoring or honest-majority assumptions. We formalize policy-soundness under chosen-message attacks (PS-CMA), extending EUF-CMA by requiring that no adversary can produce a valid signature for any message whose induced action violates the policy predicate. We prove that BBS achieves PS-CMA security under standard assumptions: binding of Pedersen commitments, collision resistance of Poseidon, and soundness of the underlying zero-knowledge proof system (e.g., Bulletproofs or PLONK). Our construction instantiates the policy predicate via a private structure function ϕ(x)\phi(x)ϕ(x) and enforces δ(x)<ε\delta(x)<\varepsilonδ(x)<ε through a zero-knowledge range constraint, while revealing no information about the private parameters. Sequential signatures compose into a hash-linked trajectory, enabling verifiable ordering and completeness of action sequences. We additionally define the Function Approximation Inversion Problem (FAIP) as a conjectured hardness property of the structure function, and emphasize that the security of BBS does not rely on this conjecture.
Open access
Cryptography and Data Security
Physical Unclonable Functions (PUFs) and Hardware Security
We introduce the ω-Protocol, a zero-knowledge proof framework for the verification of elliptic curve–based homomorphic digital signatures. The protocol is constructed on top of the Elliptic Curve Homomorphic Digital Signature Algorithm (EHDSA) and enables zero-knowledge verification of signature validity while preserving signer privacy. The core contribution of the ω-Protocol is a signature-integrated zero-knowledge construction that combines homomorphic properties of EHDSA with algebraic commitment mechanisms over elliptic curve groups. We formalize the protocol model and define security notions capturing zero-knowledge, soundness, and unlinkability of signature verification. Under standard cryptographic assumptions over elliptic curve groups, we prove that the ω-Protocol achieves zero-knowledge and unforgeability-preserving verification without revealing signature components or ephemeral key material. We further analyze the computational complexity of the protocol and show that it incurs only minimal overhead compared to standard EHDSA verification. Our results establish a principled cryptographic framework for zero-knowledge verification of homomorphic digital signatures and provide a foundation applicable to privacy-preserving authentication and verification protocols.
Michael Adjedj, Constantin Blokh, Geoffroy Couteau, Arik Galansky · 6 authors
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 Boneh, Haitner, Lindell, and Segev (EUROCRYPT 2025) achieves two rounds but 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 protocol can be transformed into an adversary that finds preimages for the ECDSA message digest function (e.g., the SHA family). Interestingly, our analysis is closely related to, and has ramifications for, the ‘presignatures’ mode of operation—Canetti, Gennaro, Goldfeder, Makriyannis, and Peled (CCS 2020), Groth and Shoup (EUROCRYPT 2022).Motivated by applications to embedded cryptocurrency wallets, where a single server maintains distinct, shared public keys with separate clients (i.e., a star-shaped topology), and with the goal of minimizing communication, we instantiate our protocol using Paillier encryption and suitable zero-knowledge proofs. To reduce computational overhead, we thoroughly optimize all components of our protocol under sound cryptographic assumptions, specifically small-exponent variants of RSA-style assumptions.Finally, we implement our protocol and provide benchmarks. At the 128-bit security level, the signing phase requires approximately 50 ms of computation time on a standard linux machine, and 2 KB of bandwidth.
Aditya Pathak, Alark Kansara, Irfan Al-anbagi, M. Shamim Hossain
In emergency response vehicular networks (ERVNs), where each second might dictate a life-or-death outcome, the performance of underlying communication systems is critical. Blockchain technology is a promising backbone for authenticating emergency response vehicles (ERVs) at smart traffic signal intersections. However, the decentralized nature of blockchain networks makes them vulnerable to distributed denial of service (DDoS) attacks. A DDoS attack can compromise safetycritical functions by overwhelming the network with fake authentication requests. Therefore, this article presents a comparative performance analysis of two well-known blockchain technologies, namely Ethereum (permissionless) and Hyperledger Fabric (HLF, permissioned), under DDoS-based network congestion. We clarify that this article does not propose any DDoS detection or mitigation mechanisms; rather, we evaluate the ability of the abovedescribed blockchains to maintain service for legitimate transactions under DDoS attacks. We design three DDoS attack scenarios that simulate realistic threats to ERVNs and benchmark throughput and latency using Hyperledger Caliper. Our results show that HLF, because of its architecture, achieves up to 2.7 times higher throughput and lower latency compared to Ethereum. This finding provides an important insight: A permissioned blockchain offers better performance under DDoS attacks, making it a more reliable communication system for safety-critical transportation systems.