We consider the enciphering of a data stream while it is being compressed by a dictionary algorithm. This scheme has to be compared to the classical encryption after compression methods used in classical security protocols. Actually, most cryptanalysis techniques exploit patterns found in the plaintext to crack the cipher and compression techniques reduce these attacks. Our scheme is based on a LZ compression algorithm in which a Vernam cipher has been included. We first present an experiment with a pseudo-random sequence generated by a simple linear feedback shift register before considering pseudo-random sequences generated by cellular automata. We make some remarks on the security by trying to measure the randomness of our method with some statistical tests. Such a scheme could be employed to increase the speed of some security protocols and to decrease the computing power for mobile devices.