September 3, 1967 is a day known as Dagen H (H day) in Sweden. On that day, all car traffic was switched from driving on the left-hand side of the road to the right side. It was the most significant logistical event to date, in the history of Sweden.

In the not too distant future, we may have what could be known as Q Day—the day in which quantum cryptography renders large swaths of traditional cryptography broken. In Cryptography Apocalypse: Preparing for the Day When Quantum Computing Breaks Today's Crypto (Wiley 978-1-119-61822-5), author Roger Grimes has written a remarkable book on how to prepare for that fateful day.

A few years ago, at RSA Conference, I asked Dr. Jane Melia of QuintessenceLabs, a quantum cryptography hardware, and software provider, why firms should consider purchasing their expensive products. She offered several reasons, one of which is that it was a hedge against broad quantum cryptography becoming mainstream, which would render much of a firm's secrets, quite public. How long that hedge will be is anyone's guess. But everyone agrees that it is inevitable. 

While quantum mechanics is weird and quite unintuitive, Grimes does a great job of explaining it in layman's terms. He provides an excellent and readable introduction to the various areas of quantum mechanics and quantum physics.

There is a perception that once quantum computing becomes fully workable, it will break all cryptography. The book makes it clear that such is not that case, and details what quantum computers will be able to break, and what they won't be able to. In short, quantum computers will be able to break any cipher algorithm whose security relies on problems related to integer factorization, discrete logarithm, elliptic-curve or any other closely related mathematical problems. What quantum computers won't be able to break are symmetric ciphers such as AES, newer integrity hashes such as SHA-2 and SHA-3. The book lists in detail what ciphers and algorithms are at risk.

While Dagen H happened overnight, Grimes writes that most changes won't happen instantly, but will occur across a multitude of timelines based on different use cases and applications. Some will be in weeks, others in months and years. But far-reaching monumental changes are coming. 

The first part of the book is introductory and theoretical, but the rest of the book is highly practical. Grimes lays out the various use cases and concrete steps one needs to take to ensure they are not blindsided by the upcoming advent of quantum cryptography. One may take the naïve approach to throw out all of their quantum vulnerable crypto and replace it with quantum-resistant solutions. But Grimes writes that one has to approach that method with caution for several reasons. Rushing prematurely into the world of quantum cryptography will likely not make things much better. 

To that, the book details how one should adequately prepare for the quantum apocalypse. It lists four major post-quantum mitigation phases and six major post-quantum mitigation project steps. It also mentions numerous vendors currently active in the quantum cryptography space. 

The question everyone in information security has to ask is this: Will your organization be protected the day a quantum computer breaks encryption? For those who want to answer that in the positive, Cryptography Apocalypse has all that you need to know to answer in the positive. The book provides the reader with nearly everything they need to know on the topic and is an essential and unique reference on the subject.