Below are some of the resources I would recommend to anyone wanting to learn more on cryptography, ans specifically for anyone
wanting to have a go at crypto challenges in CTFs. Please note these recommendations are highly subjective.
If you are interested to get started in cryptography I would highly recommend the book Serious Cryptography by JP Aumasson.
It not only deals with the fundamental concepts, but also illustrates, using examples, what could (and does) go wrong in real-life implementations.
Introduction to Modern Cryptography by Jonathan Katz
and Yehuda Lindell is an excellent book covering the basics - it is used by a lot of universities as course material for cryptography courses. A third good book is
Understanding Cryptography by Christof Paar and Jan Pelzl. Whats is extra nice about this book is that
there is an accompanying YouTube channel with lectures by Christof Paar based on the content of the book.
If you are interested in getting a deeper understanding of (the beauty of) the mathematical concepts of a.o. finite fields and elliptic curves (which I fully recommend), the book
A Classical Introduction to Modern Number Theory by Kenneth Ireland and Michael Rosen or the book
The Arithmetic of Elliptic Curves by Joseph Silverman (who has written much more eleborate and more complex books on elliptic curves) give more mathematical details on these subjects.
The Coursera Crypto I course by Dan Boneh (Stanford) is an excellent time investment if you want to learn
The following platforms allow you to test and train your skills with online challenges:
The following tools are very helpful when solving crypto challenges
Here are some hopefully useful pointers on how to get started with playing CTFs
Here is a non-complete list of cryptographers I find insightful, you might want to follow then on Twitter: