There are a lot of books on encryption. Is there a must read intro, something like Smashing the Stack for Fun and for profit, that more or less everyone reads?
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Historically, there's no computer, let alone Python code. Encryption systems have been designed and attacked and improved since many centuries before the invention of electricity. Also, only the most basic, weakest, puniest forms of encryption can be described as "unordered data".
The really must-read introduction on cryptography and decryption is this classic text. It is free (in all meanings). French speakers may want to read this remarkable translation. This simple text is quite entertaining, extremely well written, and will plant the right ideas in the reader's mind.
Afterwards, find an introductory book. I have read that one; it is not bad. Cheap pocket editions exist, and you may find it in many libraries too. Further exploration of the subject will entail doing some maths (not very complex maths, but a lot of maths). A very good resource for that advanced stage is the Handbook of Applied Cryptography, which is quite thorough, precise, full of references, and can be downloaded for free.