Conference/Journal publication author's name (surname)? I am just wondering if I can legally use a nickname or not to use my official name (Passport name) as the author's name of a conference or a journal publication? 

My official name is quite long and I am planning to change it in the future. Is it possible to put the name that I am going to call myself in the future as the author's name?
There is no requirement to use your full, legal name when publishing a paper. Many people who get married continue to use the same name they used before marriage, even if they change their surname to match their partner's, to ensure all their publications can be found easily. It actually would be quite unusual for authors to use their full name when publishing. English "middle names" are usually omitted or shortened to just an initial.