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A unified theoretical framework for steganography: balancing reliability, security and robustness
Get PDFThis paper presents a unified information-theoretic framework for steganography that simultaneously addresses reliability, statistical undetectability, computational security, and robustness over noisy channels. Unlike prior work that treated these aspects separately under idealized assumptions, the framework formalizes them within a single model, providing definitions, capacity bounds, and impossibility results based on statistical distances. It also considers computationally bounded adversaries and trade-offs between payload, detectability, and error, offering a rigorous foundation for designing secure, robust, and efficient steganographic systems
On the Security of Linear Secret Sharing with General Noisy Side-Channel Leakage
Get PDFSecret sharing is a foundational cryptographic primitive for sharing keys in distributed systems. In a classical -threshold setting, it involves a dealer who has a secret, a set of users to whom shares of the secret are sent, and a threshold which is the minimum number of shares required to recover the secret. These schemes offer an \textit{all-or-nothing} security approach where less than shares reveal no information about the secret. But these guarantees are threatened by side-channel attacks which can leak partial information from each share. Initiated by Benhamouda et. al. (Crypto\u2718), the security of linear secret sharing schemes has been studied for bounded leakage models, which assume that the adversary can leak bounded functions of each share. However, this model does not translate into real-world attacks, as physical side-channels are inherently noisy. The -noisy channel model, proposed by Prouff and Rivain (Eurocrypt’13), is a general leakage framework which captures the noisy behaviour of side-channels. But the security for this model has proven difficult to analyze even for -threshold schemes. The best known guarantees due to Duc et. al. (Eurocrypt\u2714), show that the adversary has at most advantage compared to guessing blindly, where is the underlying field. In this work, we study the security of linear secret sharing schemes with -noisy leakage, and show bounds on the mutual information (MI) and statistical bias () security metrics. Our results are based on the Fourier analytical framework, first used by Benhamouda et. al. (Crypto\u2718), adapted to the -noisy model. Informally, for some security parameter , the Poisson\u27s summation formula enables us to bound the ratio between the observed leakage for some given secret, and leakage under independence as . This is then used to show a) -threshold schemes over have at most leakage, given ; and consequently b) for -threshold schemes the guessing advantage is at most . Our results for the first time remove the field-size loss in security guarantees for -threshold schemes. Furthermore, for -threshold schemes, our results imply that the known security barrier of is an artifact of the bounded leakage model. This work can be viewed as a next step towards closing the gap between theory and practice in leakage resilient cryptography
Unforgettable Fuzzy Extractor: Practical Construction and Security Model
Get PDFSecure storage of private keys is a challenge. Seed phrases were introduced in 2013 to allow wallet owners to remember a secret without storing it electronically or writing it down. Still, very few people can remember even 12 random words. This paper proposes an alternative recovery option that utilizes lower-than-standard entropy secrets (such as passwords, biometrics, and object extractors). It can be used on its own (in combination with strong key derivation functions) or provide an additional backup option for the existing mnemonics. In this work, we investigate several aspects of secure key derivation: (1) how much entropy different sources can provide; (2) what is the preferred construction of the fuzzy extractor; (3) our key contributions in the selected approach; (4) the main security assumptions and properties of Unforgettable Fuzzy Extractor; (5) economic rationale for parameters (e.g., fuzzy vault size, additional PoW difficulty, secret length, cost of the attack) achieving the optimal solution from both security and time perspectives
Zero-Downtime Post-Quantum TLS 1.3 Migration: A Bridge-Server-Based Approach
Get PDFThe rapid advancement of quantum computing threatens the security of widely deployed public-key cryptosystems, creating an urgent need for practical migration to post-quantum cryptographic (PQC) standards. Although the U.S. National Institute of Standards and Technology (NIST) and Korea’s KpqC initiative have recently standardized PQC algorithms, integrating them into Transport Layer Security (TLS)~1.3 remains operationally challenging. Larger certificates, higher handshake costs, and incompatibility with legacy clients make naive deployment impractical in production environments.
While hot reload has long been supported in classical TLS deployments (e.g., Nginx, HAProxy), these mechanisms were designed for RSA/ECC contexts with small keys and certificates, and they do not address PQC-specific challenges.
This work presents a systematic demonstration of \emph{hot reload and rollback in a PQC-enabled TLS context}, incorporating a policy-driven state machine for staged migration and rollback under realistic constraints such as increased handshake latency and legacy-client compatibility. We propose a bridge-server-based framework that operates at the TLS library level, enabling zero-downtime migration across classical, hybrid, and PQC deployments. Experimental evaluation shows that PQC handshakes incur a
5.8--6.4 increase in latency in compute-bound settings relative to ECC baselines, while the relative overhead is significantly smaller in network-bound scenarios, highlighting the importance of deployment context.
These findings provide a feasible path toward secure and incremental PQC integration in TLS infrastructures, contributing to broader strategies for achieving crypto-agility under evolving cryptographic standards
On the Security of SL-DNSSEC
Get PDFThe proposed protocol (AsiaCCS\u2725) uses a quantum-safe KEM and a MAC to perform signature-less DNSSEC validations in a single UDP query / response style. In this paper, we give a formal analysis of in the reductionist model
Threshold Signatures from One-Way Functions
Get PDFA threshold signature allows one to delegate its signing rights to parties, such that any subset of size can sign a message on their behalf. In this work, we show how to construct threshold signatures for any and from one way functions, thus establishing the latter as a necessary and sufficient computational assumption. Our protocol makes non-black box use of one-way functions, and can be generalized to other access structures, such as monotone policies
NISQ Security and Complexity via Simple Classical Reasoning
Get PDFWe give novel lifting theorems for security games in the quantum random oracle model (QROM) in Noisy Intermediate-Scale Quantum (NISQ) settings such as the hybrid query model, the noisy oracle and the bounded-depth models.
We provide, for the first time, a hybrid lifting theorem for hybrid algorithms that can perform both quantum and classical queries, as well as a lifting theorem for quantum algorithms with access to noisy oracles or bounded quantum depth.
At the core of our results lies a novel measure-and-reprogram framework, called hybrid coherent measure-and-reprogramming, tailored specifically for hybrid algorithms. Equipped with the lifting theorem, we are able to prove directly NISQ security and complexity results by calculating a single combinatorial quantity, relying solely on classical reasoning.
As applications, we derive the first direct product theorems in the average case, in the hybrid setting - i.e., an enabling tool to determine the hybrid hardness of solving multi-instance security games. This allows us to derive in a straightforward manner the NISQ hardness of various security games, such as (i) the non-uniform hardness of salted games, (ii) the hardness of specific cryptographic tasks such as the multiple instance version of one-wayness and collision-resistance, and (iii) uniform or non-uniform hardness of many other games
Rhizomes and the Roots of Efficiency—Improving Prio
Get PDFPrio, tailored under privacy-by-design principles, is a protocol for aggregating client-provided measurements between non-colluding entities. The validity of measurements is determined by using a fully linear probabilistically-checkable proof (FLPCP). The Prover distributes secret shares of the measurement and the proof to multiple Verifiers. These Verifiers can only use linear queries on the input statement for validation without accessing the actual measurement. Efficiency is key for the practical application of Prio. The FLPCP operates with polynomials represented in the Lagrange basis using roots of unity as the nodes. However, we observe opportunities to improve its performance by embracing the Lagrange basis more extensively. For instance, we show an inversion-free O(n) time-complexity algorithm for polynomial evaluation in the Lagrange basis (an alternative to the classic rational barycentric formula). By applying our methods to libprio-rs, a cutting-edge Rust implementation, the Sharding phase (proof generation) runs a 36% faster and the Prep-Init phase (proof verification) is twice as fast, showing a substantial acceleration of the most time-consuming phases of Prio
Efficient Aggregate Anonymous Credentials for Decentralized Identity
Get PDFAnonymous credential schemes allow users to prove claims about themselves in a privacy-preserving manner. Put simply, a user can prove that she has an attribute value (e.g., she is a citizen) without revealing any other information about herself. Traditional schemes (including those with multiple credential issuers) operate under the assumption that each recognized issuer produces credentials for all user attributes. This assumption, however, is not practical: in the real world, no such issuer exists; an identity provider today issues a user credentials for a subset of user attributes, not all. A promising approach to support this setting is aggregate anonymous credentials, which allow a user to receive credentials from several issuers such that she can aggregate them and prove various claims about her attribute values in one shot. In this paper, we first introduce what we call aggregate tag-based signatures and describe an efficient instantiation. We then leverage the latter together with structure-preserving signatures and signatures of knowledge to construct an efficient aggregate anonymous credential scheme. We finally, formally evaluate the security of the proposed schemes and run benchmarks to showcase the practicality of the resulting scheme and its relevance for decentralized identity applications
Space-Deniable Proofs
Get PDFWe introduce and construct a new proof system called Non-interactive Arguments of Knowledge or Space (NArKoS), where a space bounded prover can convince a verifier they know a secret, while having access to sufficient space allows one to forge indistinguishable proofs without the secret.
An application of NArKoS are space-deniable proofs, which are proofs of knowledge (say for authentication in access control) that are sound when executed by a lightweight device like a smart-card or an RFID chip that cannot have much storage, but are deniable (in the strong sense of online deniability) as the verifier, like a card reader, can efficiently forge such proofs.
We construct NArKoS in the random oracle model using an OR-proof combining a sigma protocol (for the proof of knowledge of the secret) with a new proof system called simulatable Proof of Transient Space (simPoTS). We give two different constructions of simPoTS, one based on labelling graphs with high pebbling complexity, a technique used in the construction of memory-hard functions and proofs of space, and a more practical construction based on the verifiable space-hard functions from TCC\u2724 where a prover must compute a root of a sparse polynomial. In both cases, the main challenge is making the proofs efficiently simulatable