## Submission + - 1978 Cryptosystem Resists Quantum Attack (technologyreview.com) 1

KentuckyFC writes:

*In 1978, the CalTech mathematician Robert McEliece developed a cryptosystem based on the (then) new idea of using asymmetric mathematical functions to create different keys for encrypting and decrypting information. The security of these systems relies on mathematical steps that are easy to make in one direction but hard to do in the other. The most famous example is multiplication. It is easy to multiply two numbers together to get a third but hard to start with the third number and work out which two generated it, a process called factorisation. Today, popular encryption systems such as the RSA algorithm use exactly this idea. But in 1994, the mathematician Peter Shor dreamt up a quantum algorithm that could factorise much faster than any classical counterpart and so can break these codes. As soon as the first decent-sized quantum computer is switched on, these codes will become breakable. Since then, cryptographers have been hunting for encryption systems that will be safe in the post quantum world. Now a group of mathematicians have shown that the McEliece encryption system is safe against attack by Shor's algorithm and all other known quantum algorithms. That's because it does not depend on factorisation but gets its security from another asymmetric conundrum known as the hidden subgroup problem which they show is immune to all known quantum attacks (although the work says nothing about its safety against new quantum (or classical) attacks).*
## Ciphertext only attack? (Score:2)

The problem with most encryption systems isn't that they will be cracked by the ciphertext alone. It's that it will be cracked by other means. Alice might be able to communicate with Bob, but it does not protect them from Eve. Basically the security of any cryptosystem is limited by the physical security of Alice and Bob which will not be very strong except in situations where a state is physically securing Alice and Bob. And while this may protect Alice and Bob from the robberhose attack and while a strong