Opacity in Discrete Event Systems and Its Enforcement via State Encryption

Dolev-Yao Information Flow

Achieving Flexible and Secure Authentication With Strong Privacy in Decentralized Networks

Anonymous credentials (ACs) are a crucial cryptographic tool for privacy-preserving authentication in decentralized networks, allowing holders to prove eligibility without revealing their identity. However, a major limitation of standard ACs is the disclosure of the issuer’s identity, which can leak sensitive contextual information about the holder. Issuer-hiding ACs address this by making a credential’s origin indistinguishable among a set of issuers. Despite this advancement, existing solutions suffer from practical limitations that hinder their deployment in decentralized environments: inflexible credential models that restrict issuer and holder autonomy, flawed revocation mechanisms that compromise security, and weak attribute hiding that fails to meet data minimization principles. This paper introduces a new scheme called IRAC to overcome these challenges. We propose a flexible credential model that employs vector commitments with a padding strategy to unify credentials from heterogeneous issuers, enabling privacy-preserving authentication without enforcing a global static attribute set or verifier-defined policies. Furthermore, we design a secure decentralized revocation mechanism where holders prove non-revocation by demonstrating their credential’s hash lies within a gap in the issuer’s sorted revocation list while maintaining issuer anonymity. IRAC also strengthens attribute hiding by utilizing zk-SNARKs and vector commitments, allowing holders to prove statements about their attributes without disclosing the attributes themselves or the credential structure. Security analysis and performance evaluations demonstrate its practical feasibility for decentralized networks, where a credential presentation can be generated within 1 second.

LICA: Making Quantum Incorrect-Plaintext Attack Detectable in Data Sharing Protocol

In Incorrect-Plaintext Attacks (IPA), a malicious Data Owner (DO) compromises system security by encrypting incorrect plaintext, while a malicious Data User (DU) undermines system fairness by falsely claiming decryption failure even when the plaintext is valid. Both security and fairness vulnerabilities can be further amplified by adversaries with quantum computing. However, currently, no existing data sharing scheme can detect such quantum IPA, making it unexplored. This paper proposes LICA, a lattice-based IBE (Identity-Based Encryption) scheme with commitment assistance to detect quantum IPA in data sharing. LICA can identify if a ciphertext is encrypted from the specified plaintext and public key. It leverages the hardness of lattice problems to achieve quantum resistance. Commitment binding the encryption random parameters prevents DU from forging valid verification proofs. Then we present a new LICA-based Data Sharing Protocol (LICADS). Upon suspected quantum IPA, a trusted arbitration authority initiates a probabilistic challenge with the DO and collects evidence from the DO and DU. Then the arbitration authority identifies the malicious party using LICA and signatures to apply penalties. LICA is not only quantum-resistant but also formally proven to achieve commitment security and zero-knowledge proof security, which enables privacy protection during the verification process. Meanwhile, LICADS is the first data sharing protocol capable of detecting quantum IPA. We formally prove that LICA satisfies commitment correctness, verification correctness, binding, privacy preservation, unforgeability and pq-IND-sID-CPA security, and that LICADS achieves fairness, ensuring that any malicious party cannot evade punishment while honest parties are never penalized. We evaluate related schemes in terms of computational overhead, communication overhead, smart contract latency, and consensus efficiency. Experimental results show that LICADS incurs computational overhead comparable to existing schemes and roughly an order-of-magnitude higher communication overhead (about 45 KB under the Module-LWE instantiation versus 4–6 KB). We regard this as a worthwhile trade-off, since LICADS is the only scheme that detects quantum IPA.

Black-Box Construction of Partial Key Exposure Resilient Symmetric-Key Encryption Scheme

In a TLS session, the user is granted access solely to the encryption and decryption oracles, ℰ ( K , · ) and 𝒟 ( K , · ) , of a symmetric-key encryption scheme, which are treated as black boxes. Here, ℰ denotes the encryption algorithm, 𝒟 the decryption algorithm, and K the secret key. In this paper, by utilizing any secure symmetric-key encryption scheme as a black-box primitive, we demonstrate a method for constructing a symmetric-key encryption scheme that remains secure even in the presence of partial key leakage. This approach can, for example, enhance the security of TLS sessions. Our construction employs the All-Or-Nothing Transform (AONT) in the pre-processing phase. Therefore we provide a tighter security analysis of existing AONT constructions, and establish a lower bound on their security. Finally we propose a new AONT construction that achieves security beyond this lower bound.

A Framework for Context-Aware Read Authorization over Encrypted Data

: Many security and privacy-sensitive systems must control access to encrypted data based on dynamic operational context, such as workflow stage, safety mode, or emergency conditions. Data producers cannot anticipate which context will apply at processing time, and the component observing context cannot be trusted with plaintext or policy structure. Existing mechanisms, including Access Control Encryption (ACE), assume that all authorization-relevant information is fixed at encryption time, and offer no mechanism to incorporate context that becomes available only after the data has been produced and forwarded. We introduce Contextual Reading ACE (CR-ACE), a framework for enforcing context-dependent read authorization without a trusted reference monitor. An honest-but-curious intermediary sanitizes sender ciphertexts and attaches public contextual attributes while remaining oblivious to message contents, principal identities, and authorization logic. Receivers locally enforce authorization as the conjunction of the global ACE policy and a contextual predicate embedded in their key material. We formalize a security model for CR-ACE, provide a construction and prove that it achieves contextual payload privacy, sender anonymity, sanitization security under context, and correct enforcement of both global and context-dependent authorization in our non-collusion model.

Hybrid Encryption for State Estimation Against Stealthy Attacks

The “crypticity” is characterized as confidentiality property that characterizes whether system information can be inferred by an attacker. When the system is uncryptic, transmission data are easily intercepted and compromised by attackers, further endangering system stability. The existing computational security in the computer field only ensures that attackers cannot recover the plaintext from the ciphertext and key in polynomial time. However, in control systems, due to system vulnerability, the attacker can directly utilize the ciphertext data to launch stealthy attacks rather than decrypting. To meet the security requirement for state estimation, this paper formulates a new crypticity-enhancing framework. A hybrid encryption strategy with low computational complexity is proposed. Specifically, symmetric encryption algorithms encrypt transmitted innovations of state estimation, while asymmetric encryption algorithms encrypt keys of symmetric encryption. A sufficient condition for partial crypticity and a necessary and sufficient condition for complete crypticity of the hybrid encryption algorithm are derived. A simulation example is presented to sustain the theoretical results.