In this paper, a security framework based on cellular automata is proposed, which is composed of three parts: entity authentication, data encryption, and decryption. Authentication is based on a zero-knowledge protocol, and its robustness is supported by the fact that the shared secret is not only an NP-complete problem but also dynamically transformed by a two-dimensional cellular automaton into a more complex secret. Thus, the authentication’s output is the key to data encryption/decryption in the following steps. One more strength of this system is the sensibility of the cellular automata to initial conditions—which is why we must know the initial configuration in order to obtain the key and the times that cellular automata evolved. All those characteristics give the system both robustness and security.