I would like to apply for a Master degree. I'm looking for a major that study both Computer and Maths. Can anyone tell me what such major are?
As an example, the University of Oxford (UK) as an MSc program in Mathematics and the Foundations of Computer Science, which not only has courses in computer science and mathematics, but in particular also offers courses on the interplay between these areas.
I'm not sure what your prior experience/work is, but if you have a little experience in Computer Science, another option is Cryptography.
Though it's usually not an explicit major, one typically studies it through a given Mathematics program, and if you concentrate on the applied side of things (i.e., writing actual algorithms and performing time/space analyses of them), you'll be deep enough in the weeds to be forced to learn more Computer Science along the way.