  The fourth generation of cell phones, marketed as 4G/LTE (Long-Term
Evolution) is being quickly adopted worldwide. Given the mobile and wireless
nature of the involved communications, security is crucial. This paper includes
both a theoretical study and a practical analysis of the SNOW 3G generator,
included in such a standard for protecting confidentiality and integrity. From
its implementation and performance evaluation in mobile devices, several
conclusions about how to improve its efficiency are obtained.
