I am a student of bsc cs .how to apply for cyber security in iit colleges.any kind of entrance exam conduct by iit.

Dear Devesh, you need to appear for IIT JAM which is an entrance examination  for M.Sc, M.Sc-Ph.D and M.Sc-Ph.D dual degree programmes at IITs. IIT Kharaghpur and IIT Kanpur have been voted and awarded amongst the top Institutions offering Cyber Security courses in India. The basic eligibility criteria is that you should have completed your Bachelor's degree with a minimum aggregate of 55%. Final year students also can apply. However IIT JAM 2019 has already been conducted and you may have to wait until next year.