A good introduction to Cryptography Excuse me in advance for the generality of the question I am about to ask, I am not even sure if this is the place to ask... but here I go!

Let me start by mentioning a little about my academic background:

I recently finished my Mathematics BSc and I am starting an MSc in Mathematics on September. I did my Final degree thesis on Tannakian Categories and I have a good background in topics such as algebraic number theory, algebraic geometry (I have a good knowledge of scheme theory) and algebraic topology. When it comes to programming, I know C, C++, Python and R.

And here's the question:

I would like to find a good book/online course in order to learn a bit about Cryptography, most preferably following a deep mathematical approach, but combining it with programming in any of the latter languages, so that I can see an application. I don't mind learning another language, by the way :)

Thanks in advance!
i think “ Introduction to Modern Cryptography “ by Jonathan Katz and
Yehuda Lindell is a very good book for your requirements.
you could also try "Foundations of Cryptography” by Oded Goldreich.