<p>The sixth generation (6G) of wireless technology marks a significant advancement with the potential to transform various fields, including the Internet of Things (IoT), fog computing, cloud computing, and blockchain, through seamless integration. One such innovation is the 6G-enabled IoT-fog system, which establishes a decentralized computing infrastructure by enabling data processing and storage closer to its origin. This approach emphasizes fog infrastructure, allowing numerous IoT devices to connect and execute applications efficiently. However, the increased connectivity heightens the risk of security attacks on fog nodes (FNs), jeopardizing data credibility, localized processing, and service efficiency. To address these challenges, this work proposes a secure blockchain scheme integrated with 6G technology to ensure data credibility in the IoT-fog environment. Specifically, it employs the Castro–Liskov (C–L) blockchain consensus mechanism combined with a credibility point (CP)-based method to detect and mitigate malicious FNs. The proposed scheme is evaluated against existing schemes, including securing fog computing with decentralized user authentication (SFCDU), Baniata et al., Priyadarshini et al., and Rastoceanu et al., focusing on processing time, detection accuracy, and energy consumption. Results demonstrate that the proposed scheme identifies malicious FNs more efficiently than its counterparts, offering a superior solution for enhancing security in the 6G-enabled IoT-fog system.</p>