The question might sound broad, allow me to explain. Cryptography is a diverse domain. I have been in Crypto research since last four years. Recently, one of my colleague got interviewed by an IT giant where he was asked some apparently random questions on AES, hash functions, randomness, entropy, RNG, block ciphers, variants of RSA etc. He was not prepared to be asked questions not related to his research; hence the interview was an epic fail in spite of him being an academically promising candidate.

The truth is, while pursuing active research in a sub-domain, it is not quite uncommon to not be able to answer questions from other sub-domain. Moreover, if the questions are more on practical side which is of an industry's interest.

What could be a good source to prepare for a similar interview? A pool of practical Crypto questions touching the fundamentals, preferably with solutions, will be a good candidate.


[Disclaimer: what follows is just my personal subjective opinion]

If the person being interviewed is a crypto researcher, this means the purpose of the interview is to have the opinion of an expert in cryptography. As such, learning high-level 'thought provoking' information about cryptography to prepare such an interview kind of misses the point, in my opinion: finding this material and reading it is something anyone with a vague scientific background could do. I do not see the point of interviewing a crypto expert if in the end he just repeats what he learned two days ago on Wikipedia.

Maybe this was a mistake of the IT giant to interview an expert and ask him question far from his field. At the same time, I believe that being an expert in any domain requires a strong knowledge of the surrounding area. Your specialized subfield exists in a broader context, has connections to other areas of cryptography. In fact, over-specialization is a plague of science, with more and more people struggling to solve problem when the solution they are looking for has already been found - under another name, perhaps, and in another but related field. There are dozen of examples of this.

So, my point is the following: if you feel like you need some high-level and generic material about crypto to answer an interviewer who contacted you based on your expertise of the field, I'd suggest refusing the interview. At the same time, I would suggest getting prepared for further interviews of this type the hard way: not through Wikipedia, nor through lists of thought-provoking questions, but through a long and dedicated study of all the fundamental results that shaped cryptography. Reading seminal papers in all major subfields of cryptography, regularly following the news through conferences, perhaps organizing a weekly seminar on breakthrough or seminal results in cryptography in your university. Even a researcher on side-channel analysis should be able to describe the GGM PRF construction. Even an expert on indistinguishability obfuscation should have a pretty good idea of the design choice behind AES, and the existing cryptanalytic techniques. Even an expert about discrete-log type cryptography should be able to describe Regev's lattice-based encryption scheme. I guess you get the point. The bonus is, not only will that allow you/your colleague to be more confident in interviews; it will also have very positive impacts on your research by allowing to envision connections to other area, and will help broaden your interactions with the scientific community.

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