I want to study the DES and AES algorithms
What are the minimum mathematics and computer science subjects that I need to understand DES and AES?
Edit: I mean how they work internally.
AES uses Polynomial Modular arithmetic in Finite Fields. These are used in the SubBytes & the MixColumns Steps.
I don't think DES uses any advanced mathematics Probability Theory for both DES & AES
So you need to understand basic Linear Algebra, Group Theory (what is a Finite Field, Ring Theory), Elementary Number Theory (Modular Arithmetic).
In Comp Science, you would need an understanding of bitwise operations.
If you want to go for a deep analysis, you would need to know Information Theory, Complexity Analysis.
UPDATE: From SAI Peregrinus in the comments:
Probability theory is also required to understand how cryptanalysis works. DES's special feature was resistance to differential cryptanalysis, so you can't really understand why DES and AES have the s-boxes they do without knowing this