The construction of virtual transportation networks requires massive data to be transmitted from edge devices to Virtual Service Providers (VSP) to facilitate circulations between the physical and virtual domains in Metaverse. Leveraging semantic communication for reducing information redundancy, VSPs can receive semantic data from edge devices to provide varied services through advanced techniques, e.g., AI-Generated Content (AIGC), for users to explore digital worlds. But the use of semantic communication raises a security issue because attackers could send malicious semantic data with similar semantic information but different desired content to break Metaverse services and cause wrong output of AIGC. Therefore, in this paper, we first propose a blockchain-aided semantic communication framework for AIGC services in virtual transportation networks to facilitate interactions of the physical and virtual domains among VSPs and edge devices. We illustrate a training-based targeted semantic attack scheme to generate adversarial semantic data by various loss functions. We also design a semantic defense scheme that uses the blockchain and zero-knowledge proofs to tell the difference between the semantic similarities of adversarial and authentic semantic data and to check the authenticity of semantic data transformations. Simulation results show that the proposed defense method can reduce the semantic similarity of the adversarial semantic data and the authentic ones by up to 30% compared with the attack scheme.

翻译：虚拟交通网络的构建需要从边缘设备向虚拟服务提供商（VSP）传输海量数据，以促进元宇宙中物理域与虚拟域之间的流通。通过利用语义通信减少信息冗余，虚拟服务提供商能够接收来自边缘设备的语义数据，并借助先进技术（例如人工智能生成内容，AIGC）提供多样化服务，使用户能够探索数字世界。然而，语义通信的使用引发了安全问题：攻击者可能发送具有相似语义信息但不同期望内容的恶意语义数据，从而破坏元宇宙服务并导致AIGC产生错误输出。为此，本文首次提出一种面向虚拟交通网络中AIGC服务的区块链辅助语义通信框架，以促进虚拟服务提供商与边缘设备之间物理域与虚拟域的交互。我们阐述了一种基于训练的针对性语义攻击方案，通过多种损失函数生成对抗性语义数据。同时，我们设计了一种语义防御方案，利用区块链与零知识证明区分对抗性语义数据与真实语义数据之间的语义相似性差异，并验证语义数据变换的真实性。仿真结果表明，与攻击方案相比，所提出的防御方法能将对抗性语义数据与真实语义数据之间的语义相似性降低高达30%。