How can I study the math behind cryptography? I am a junior in high school and I am currently studying algebra 2. Where can I go to learn about the mathematics behind cryptography? I have a very basic knowledge of cryptography, but I am really interested in things like, why is a 2^256 bit cipher so secure? I would really like to learn about things like that so I can learn to make my own and analyze other ciphers.

Are there any good books or websites where I could learn about cryptography from a mathematical perspective?
Speaking from my own experience, Nigel Smart's book Cryptography: An introduction is a good place to start. I would say that you can read and understand it without any prior knowledge of cryptography at all. It is also free.