We consider the enciphering of a data stream while being compressed by a LZ algorithm. This has to be compared to the classical encryption after compression methods used in security protocols. Actually, most cryptanalysis techniques exploit patterns found in the plaintext to crack the cipher; compression techniques reduce these attacks. Our scheme is based on a LZ compression in which a Vernam cipher has been added. We make some security remarks by trying to measure its randomness with statistical tests. Such a scheme could be employed to increase the speed of security protocols and to decrease the computing power for mobile devices.