With the advancement of information hiding techniques, generation-based coverless steganography has emerged as an alternative to traditional methods, leveraging generative models to transform secret information into stego-objects rather than embedding it within the redundancy of the cover. However, existing generation-based approaches require pseudo-keys that must be shared between communication parties, leading to high overhead of frequent key exchanges and security risks due to their tight coupling with the secret information. This paper proposes a DDIM-driven coverless steganography scheme that utilizes a real-key mechanism, improving the key management. By integrating reversible data hiding (RDH) and chaotic encryption into generation model, the proposed method eliminates excessive key exchanges and reduces the correlation between the key and the secret information. Furthermore, it requires only a single key negotiation for multiple communication, which lowers overhead. Experimental results demonstrate that the proposed scheme resists substitution attacks, enhancing the security of covert communication.