Policy-controlled signature (PCS) was introduced by Pairat Thorncharoensri et al. at ICICS 2009, and improved at Computer Standards & Interfaces 2017. In this type of digital signature, signer can sign a message with some policies. Any verifier who does not satisfies the policies cannot verify the message. They also extended the notion of policy-controlled signature, and called it "universal policy-controlled signature". In their extended notion, they improve the flexibility of the PCS scheme by allowing a third party to equip the signature with policy, rather than the signer. In this work, we use the recent techniques in lattice to construct policy- controlled based signature from NTRU lattice. In particular, we adapt Léo Ducas et al.'s encryption and signature protocol on lattice (ASIACRYPT 2014), and combine them with Pairat Thorncharoensri et al.'s work to satisfy the properties of policy-controlled signature. Our contribution is developing the first quantum- resistant schema based on the policy-controlled signature.
Policy-controlled signature (PCS) was introduced by Pairat Thorncharoensri et al. at ICICS 2009, and improved at Computer Standards & Interfaces 2017. In this type of digital signature, signer can sign a message with some policies. Any verifier who does not satisfies the policies cannot verify the message. They also extended the notion of policy-controlled signature, and called it "universal policy-controlled signature". In their extended notion, they improve the flexibility of the PCS scheme by allowing a third party to equip the signature with policy, rather than the signer. In this work, we use the recent techniques in lattice to construct policy- controlled based signature from NTRU lattice. In particular, we adapt Léo Ducas et al.'s encryption and signature protocol on lattice (ASIACRYPT 2014), and combine them with Pairat Thorncharoensri et al.'s work to satisfy the properties of policy-controlled signature. Our contribution is developing the first quantum- resistant schema based on the policy-controlled signature.
In recent years, there has been much focus on developing core cryptographic primitives based on lattice assumptions, driven by the NIST call for post-quantum key encapsulation and digital signature algorithms. However, more work must be conducted on efficient privacy-preserving protocols based on quantum-safe assumptions. Electronic voting is one such privacy-preserving protocol whose adoption is increasing across the democratic world. E-voting offers both a fast and convenient alternative to postal voting whilst further ensuring cryptographic privacy of votes and offering full verifiability of the process. Owing to the sensitivity of voting and its infrastructure challenges, it is crucial to ensure security against quantum computers is baked into e-voting solutions. We present an e-voting scheme from quantum-safe assumptions based on the hardness of the RLWE and NTRU lattice problems, providing concrete parameters and an efficient implementation. Our design achieves a factor 5.3 × reduction in ciphertext size, 2.5 × reduction in total communication cost, and 2 × reduction in total computation time compared to the state-of-the-art lattice-based voting scheme by Aranha et al. (ACM CCS 2023). We argue that the efficiency of this scheme makes it suitable for real-world elections. Our scheme makes use of non-ternary NTRU secrets to achieve optimal parameters. In order to compute the security of our design, we extend the ternary-NTRU work of Ducas and van Woerden (ASIACRYPT 2021) by determining the concrete fatigue point (for general secrets) of NTRU to be q = 0.0058 · σ 2 · d 2.484 (above which parameters become overstretched) for modulus q , ring dimension d , and secrets drawn from a Gaussian of parameter σ . We consider this relation to be of independent interest and demonstrate its significance by improving the efficiency of the (partially) blind signature scheme by del Pino and Katsumata (CRYPTO 2022).
Blind signatures were first introduced by David Chaum. They allow a user to have a message signed by a signer without revealing the message itself. This property is particularly useful in applications such as electronic voting and digital cash, where user anonymity is important. In a blind signature scheme, the user blinds their message before sending it to the signer, who signs the blinded message. The user then unblinds the signed message to obtain a valid signature that can be verified publicly, ensuring that the signer cannot trace the signed message back to the original unblinded version. A good analogy is placing the message inside an envelope and having the envelope signed. Once the envelope is opened, the signature remains valid for the enclosed message, ensuring that the content remains confidential. Such constructions provide anonymity and privacy to the user but given a practical quantum computer, the security of traditional crypto-systems providing such features will be broken. To address this, the development of quantum-resistant cryptographic protocols is essential for maintaining the security of digital transactions and data. Aligning with the same goal, this work aims to thoroughly review the background of lattice-based blind signatures. We start with the foundations of digital signatures in the classical settings and then move on to lattice-based constructions.
Blind signatures are a central tool for privacy-preserving protocols. They allow users to obtain signatures from a signer without the signer seeing the signed message. For instance, it enables electronic cash: signatures correspond to coins which can be issued by the bank in a privacy-preserving manner via blind signing. To mitigate the risk of key compromise, threshold blind signatures allow the distribution of the signing key amongst N parties. While recent works have focused on improving the security of this primitive in the classical setting, no construction is known to date in the post-quantum setting. We present the first construction of a threshold blind signature secure in the post-quantum setting, based on lattices. We prove its security under an interactive variant of the SIS assumption introduced in [Agrawal et al., CCS’22]. Our construction has a reasonable overhead of a factor of roughly 1.4 X to 2.5 X in signature size over comparable non-threshold blind signatures over lattices under heuristic but natural assumptions.
Digital signature with proxy delegation, which is a secure ownership enforcement tool, allows an original signer to delegate signature rights to a third party called proxy, so that the proxy can sign messages on behalf of the original signer. Many real-world applications make use of this secure mechanism, e.g., digital property transfer. A traditional digital signature mechanism is required to bind a message and its signature together for verification. This may yield extra cost in bandwidth while the sizes of message and signature are relatively huge. Message recovery signature, enabling to reduce the cost of bandwidth, embeds a message into the corresponding signature; therefore, only the signature will be transmitted to the verifier and the message can further be recovered from the signature. In this paper, we, for the first time, propose a novel digital signature scheme in the identity-based context with proxy delegation and message recovery features and, more importantly, our scheme is quantum resistant, in a particular lattice-based signature. Our scheme achieves delegation information and signature existential unforgeability against adaptive chosen warrant and identity. Compared with the seminal lattice-based message recovery signature, our scheme is independent from public key infrastructure, realizes delegation transfer of signature rights, and compresses signature length ulteriorly. To the best of our knowledge, this paper is the first of its type.
Although the current lattice-based ring signcryption scheme resists quantum attacks,it has large key storage and high encryption/decryption time.The linkable lattice ring signcryption scheme not only can protect signer anonymity,but also can determine whether two signatures are generated by the same signer.Thus,based on the compact Gaussian sampling algorithm and rejection sampling technique,the identity-based linkable ring signcryption scheme is constructed on the NTRU lattice.Firstly,the system master key is generated using the trapdoor generation algorithm on the NTRU lattice.Then private keys of ring members are obtained based on the compact Gaussian sampling algorithm.Finally,the user signature is generated using rejection sampling,and the key encapsulation mechanism encrypts the signature.Security proof in the random oracle model (ROM) that DRLWE and NTRU small integer solutions are difficult to solve ensures confidentiality,unforgeability,unconditional anonymity,and linkability.Performance analysis shows that compared to the lattice-based ring signcryption and linkable ring signature schemes on NTRU,the proposed scheme has a smaller public key and lower encryption/decryption cost,greatly improving efficiency.
A signcryption scheme provides both the function of digital signature and encryption scheme at the same time. Additionally, it has lower cost than traditional sign-then-encrypt or encrypt-then-sign approaches. Many useful applications have been found where confidentiality and non-repudiation are both required. On the other hand, with the current development of rapid quantum computing, currently schemes based on traditional numerical assumptions (e.g., decisional Diffie-Hellman assumption) are more likely to be attacked by quantum computers. Therefore, lattice-based signcryption schemes have been extensively studied in recent years. However, most of them are either inefficient or secure-proved under the assumptions of random oracles. Although some of them are proved in the standard model, they are not practical in low-cost devices. Since the security is based on "Learning with Errors" (LWE) or "Short Integer Solution" problems, it will result in extremely large size of keys. In this paper, we propose an efficient NTRU-based signcryption scheme, which is inspired from Pion et al.'s key encapsulation mechanism. We provide rigorous security proofs for the confidentiality and unforgeability under NTRU-based assumptions in the standard model. Compared with other schemes, we conclude that our scheme is more efficient and secure.