<p>Naveed, I am sorry that I don’t really know too much about computer science. But I did my undergraduate in EE and Physics so I know how prepared EE students are. I think you can pursue theory if you want still. But if you don’t and rather want to work on a more design based research, maybe apply to some more technical based fields is easier, such as programming language and computer architecture. I think you can change after you get in. However, you should check this online. Because I think my friends who is doing crytography at Harvard did his undergraduate in math. He is actually not in Harvard computer science but he is in Harvard Applied Math. I think most crytography requires a lot of math such as number theory and things like that. But I might be wrong. Things like computational complexity is basically math. But you should consult some experienced computer science students here because I am really not an expert in computer science.</p>