Reddit mentions of In Code: A Mathematical Journey

The Turing Omnibus has a bit of that sort of thing. It is mainly focused on computer science, and features some anecdotes about the uses of the techniques explained. This book has a lot of contributors, so the tone varies a bit from chapter to chapter, but it introduces a lot of topics.

In Code examines the RSA (and goes into a bit of depth about Modular Arithmetic) as well as the author's exploration of an alternative encryption.

Aha! Insight and The Number Devil are good books too. They're both aimed at younger readers, and feature lots of illustrations but focus more on thinking about numbers (and problems) than the mechanics of doing calculations.

I presume this is your daughter. I have a couple of book recommendations for her. This book is about a young female mathematicians journey into the world of cryptography. It may be a little advanced for her mathematically (indeed most adults won't understand all the maths) but it shows what is possible and it's a well written book.

Another great book is Alex's adventures in numberland. It shows some really fun things about maths.

The stories about Bitcoin are mostly the same old ideas being regurgitated without an understanding of what they really mean. Understanding the maths and cryptography behind is much more interesting and will lead to better things in the future.

I would suggest:

In Code: A Mathematical Journey by Sarah Flannery

The Double Helix: A Personal Account of the Discovery of the Structure of DNA by James Watson

There are an infinite number of such problems. Simply create your own. This might seem "silly" but some "silly" math ideas (another Conway idea) have turned out to have broad-ranging implications. Math arises at the intersection of deduction, aesthetics and creativity. This lecture contains a nice demonstration of the NP-completeness of generalized Super Mario Brothers -- "silly" context, but very serious math problem. Many mathematicians focus on the deduction part, fewer focus on the aesthetics part, and far fewer on the creativity part. Mathematics is like an infinite ocean containing an infinite number of islands that are each completely unique from all other islands ever discovered. Go forth and explore!