{"id":11941,"date":"2019-07-09T14:07:50","date_gmt":"2019-07-09T13:07:50","guid":{"rendered":"https:\/\/www.riskinsight-wavestone.com\/?p=11941"},"modified":"2020-01-02T11:22:02","modified_gmt":"2020-01-02T10:22:02","slug":"post-quantum-cryptography","status":"publish","type":"post","link":"https:\/\/www.riskinsight-wavestone.com\/en\/2019\/07\/post-quantum-cryptography\/","title":{"rendered":"Status of post-quantum cryptography"},"content":{"rendered":"

Quantum computers have given rise to a raft of hopes and fears. Their computing capabilities could enable us to solve certain problems more quickly than today’s computers<\/strong>, including those upon which modern cryptography is based. Does this mean that the advent of quantum computing will mark the end of cryptography as we know it? And, if so, what contribution can post-quantum cryptography<\/strong> bring to this new paradigm?<\/em><\/p>\n

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The quantum computer is slowly becoming a reality<\/h2>\n

The field of quantum computing has seen many advances since the early research of the 1980s\u2014especially that of Richard Feynman[i]<\/a>, and the emergence of the first quantum algorithms<\/strong> in the 1990s. The first prototype quantum computers<\/strong> appeared in the 2000s and, since the beginning of the 2010s, there has been a proliferation of substantive and encouraging announcements<\/strong> in the area. These include D-Wave Systems\u2019s launch of the first commercial quantum computer[ii]<\/a>, IBM\u2019s development of a cloud-based quantum machine[iii]<\/a>, and Google’s recent announcement on its new quantum processor[iv]<\/a>. On a European scale, there has also been the launch of Atos\u2019s quantum simulator,[v]<\/a> which can test and optimize quantum algorithms for use in real conditions.<\/p>\n

As we\u2019ve discussed in a previous article[vi]<\/a>, the fundamental difference between conventional and quantum computers is that traditional machines work on a series of bits whose value is equal to 1 or 0, while quantum computers work on qubits whose value corresponds to a superposition of states[vii]<\/a><\/strong>. For a given problem, it\u2019s sometimes possible to write a quantum algorithm which\u2014by making use of this superposition of states<\/strong> and the quantum entanglement[viii]<\/a><\/strong> principle\u2014can solve it more quickly than a conventional algorithm<\/strong>. Since such quantum acceleration can only be applied to a limited set of problems (i.e. those for which it’s possible to write a quantum algorithm) it\u2019s likely that, in the future, quantum computers will be used in addition to\u2014rather than in place of\u2014conventional computers.<\/p>\n

Today’s quantum computers have only a very small capacity<\/strong>. Google’s quantum processor is rated at 72-qubits, while Intel recently announced the development of a 49-qubit quantum processor[ix]<\/a>. As an illustration, Google estimates that the number of qubits needed for a real application is between one and ten million<\/strong>. The main difficulty in designing a larger quantum computer lies in the fact that all external interactions induce the phenomenon of quantum decoherence<\/strong>\u2014which means that the quantum entanglement<\/strong> it needs to operate can\u2019t be maintained[x]<\/a>. The higher the number of qubits, the more difficult it is to maintain the state of coherence. Doing so requires the system to be isolated at very low temperatures. In view of the current state of development, and the challenges still to be overcome, we may still be a long way from quantum computers being used in any practical application.<\/p>\n

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Classical cryptography\u2019s applications<\/h2>\n

To understand the implications of quantum computers for cryptography, we first need to understand the principles of classical cryptography\u2014and its applications.<\/p>\n

Classical cryptography involves several different types of algorithms:<\/p>\n