A blockchain is a distributed ledger that allows users to exchange information without a centralized authority. This technology enables users to send and receive tokens among other applications, such as transactions, product management, and elections. It is possible to send data and tokens inside a single blockchain, but a method to efficiently share the data and tokens among different blockchains has not yet been constructed. Cross-chain communication, the focal point of several recent research efforts, is a scheme for sending data or tokens among different blockchains. In existing studies, a trusted third party (TTP) is used to ensure fair rates of token exchange among different blockchains. However, because blockchains are originally designed with a policy that does not incorporate the use of TTPs, the fair exchange rate should not be determined by TTPs, but rather by the market price of tokens among users. When exchange rates are determined from quotes among users, the preferred scheme is to determine the exchange rate offered by many users as an auction. Here, some existing cross-chain communication systems use smart contracts that automatically execute arbitrary processes on the blockchain. However, such schemes require a gas fee each time a smart contract is executed. Thus, implementing an auction scheme that determines the fair exchange rate among different blockchains would necessitate each user to pay a fee for each new token offered, which would result in high gas fees. In this study, we propose a scheme to determine exchange rates from quotes among users with a relatively low gas fee. Using a first-price sealed-bid auction and commitment scheme, the user with the highest token value can be identified without revealing the other users’ token offer values. In our scheme, the largest token value among users is determined as the exchange rate using an external Smart Contract (SC) instead of a TTP. We further modify the existing insert key-value commitment scheme to aggregate the commitment values of token offers. Our scheme is based on the generalized RSA assumption. By proving that it satisfies the key-binding property, we prove that the token sender cannot act maliciously. We further implement the proposed scheme and demonstrate that the gas fees and data space required to implement the proposed scheme are practically feasible. Copyright © 2026 The Institute of Electronics, Information and Communication Engineers.

A blockchain is an important component in the design of secure distributed file systems, such as cryptocurrencies. One of the key components of the blockchain is the key-value commitment scheme, which constructs a commitment value from two inputs: a key and a value. In a conventional commitment scheme, a single user constructs a commitment value from an input value, whereas in a key-value commitment scheme, multiple users construct a commitment value from their keys and values. Both conventional and key-value commitment schemes must satisfy binding and hiding properties. The key-binding and key-hiding properties guarantee that neither the sender nor the verifier can act maliciously. The concept of a key-value commitment scheme was first proposed by Agrawal et al. in 2020 using a strong RSA assumption. Their scheme satisfies the key-binding but not key-hiding properties. In this paper, we propose two lattice-based key-value commitment schemes, Insert-KVCm/2,n,q,beta and KVCm,n,q,beta , that satisfy both the key-binding and the key-hiding properties. The key-binding property of both Insert-KVCm/2,n,q,beta and KVCm,n,q,beta are proven under the short integer solution ( SIS infinity n,m,q,beta ) problem. The key-hiding property of both Insert-KVCm/2,n,q,beta and KVCm,n,q,beta are proven under the Decisional- SISn,m,q,beta infinity -form problem, which is newly defined in this paper. We demonstrate the difficulty of the Decisional- SISn,m,q,beta infinity -form problem by showing that the Decisional- SISn,m,q,beta infinity -form problem is secure when the SISn,m,q,beta infinity problem is secure. Finally, we analyze the computational costs of Insert-KVCm/2,n,q,beta and KVCm,n,q,beta . Our method is the first lattice-based key-value commitment scheme with proven the key-binding and the key-hiding properties.

Text-to-image generation is trending in the generative artificial intelligence (GenAI) field. Among open-sourced image generation projects, Stable Diffusion is the state-of-the-art. Many artists and service providers customize the diffusion model to generate featured high-quality images. However, there is no protection to the privacy of the input text prompt, output image, and customized model. Privacy is very important since it can increase users' willingness to use the service and protect the service provider's intellectual property. Existing privacy-preserving diffusion model require fully homomorphic encryption (FHE) to ensure its privacy and security. Nonetheless, FHE is very time-consuming and may reduce accuracy due to approximations and deteriorate image quality. In this research, we propose Privacy-Diffusion, a privacy-preserving diffusion framework without FHE. By utilizing the irreversible property of neural network layers and the property that the predicted noise in the diffusion process is a normalized Gaussian distribution. Our framework can be applied to all kinds of diffusion models to protect clients' input text prompt and the generated image from being learned by the server, as well as customized models from being learned by the clients. Our protocol is secure and efficient. Compared with existing research, HE-diffusion, which spent 200% extra time and visible quality loss, our protocol can reach the same security level with only 19% extra time and has no quality loss. To the best of our knowledge, our Privacy-Diffusion is the first protocol that achieves this goal without using FHE and maintain the same high-quality image output as the original model.

Commitment schemes are cryptographic schemes that can be applied to zero-knowledge proof construction and blockchain construction. Recently, lattice-based cryptography has been intensively investigated due to the promising potential in quantum cryptography. Accordingly, commitment schemes based on lattice assumptions have been studied for practical applications. Notably, applications often require committing an arbitrary message with low communication costs, so commitment schemes must be satisfied with fewer length restrictions and fewer extensions to the messages. Several studies have been conducted to achieve the problem, including the study published by Baum et al. in 2018. However, the scheme in question still utilizes the message domain for extraneous purposes. We design a length-extension-free commitment scheme ComMWM in which the length of the message string is large relative to the length of the commitment string, improving on the commitment scheme of Baum et al. Furthermore, we prove that the hiding and binding properties of ComMWM are based on the hardness of the decisional search knapsack problem and extended search knapsack problems, respectively. Finally, we evaluate the computation costs of generating commitment value between ours and Baum et al.’s commitment scheme. Authors