To obtain a degree in cryptography, per se, it will probably be necessary for you to pursue a Master's or a doctorate (PhD) degree. My searches of undergraduate programs -- even at the best computer science and mathematics institutions in the world -- do not reveal any undergraduate degrees in cryptography.
In fact, because cryptography is both algorithmic and mathematical in nature, you can probably pursue such a course of study in either a mathematics or a computer science program. Guessing from your name that you might be on the Indian sub-continent, the Indian Institute of Technology (IIT) is a highly regarded academic program with offerings and faculty that could support such a course of study. Here in the United States, the best schools for cryptography include MIT, Carnegie-Mellon University, Purdue University, Stanford University and the University of Washington (Seattle).
I hope this reply manages to answer your question and to address your concerns. If not, please feel free to write again.
For more on this topic, visit these other SearchSecurity.com resources:
Tech Tip: Tales from the crypto, part one
Executive Security Briefing: Public key cryptography Q&A
This was first published in September 2002