I apologize as this question is not really mathematical, and therefore perhaps not well-suited for this site. Please feel free to close it if you think it is not. My reason for asking it here is that I am not satisfied (that is not convinced in any sense) by many discussions relative to that question I have seen on various forums (in particular some devoted to bitcoins),

So, the basic fact is that currently used method of cryptography, based on prime factorizations or elliptic curves, would not work anymore when a quantum computer is available, as proved by Shor. My main question is:

Do we know other cryptographic algorithms that would work in a world were quantum computers exist ?

If yes, will they be easy to implement quickly when quantum computers appear ? If not, are people working on this ? have we hope to find such algorithms anytime soon ? Is there some theoretical obstruction to the existence of such algorithm ?

To be honest, let me give more argument to close the question by indicating my motivation for asking this question, which is not mathematical. I am curious about the real-world implications of quantum-computers in particular on bitcoins. Cryptography is currently used in many transaction using real-world currencies and, by design, in all transactions using bitcoins. If cryptography became unusable because of the appearance of quantum computers, either for ever or for a sufficiently long period of time (in years), this would likely have enormous implication on the economy and the real world. To be sure, real money have worked for centuries without cryptography and if needed, one could go back to this. But cryptography and anonymity seems embedded in bit coin in a fundamental way, so would the appearance of quantum computers doom bitcoin?

Code Book. – Chandan Singh Dalawat Apr 20 '13 at 16:10mainlysym crypto not asym crypto is used). To add to this the two main big 'standard' searches related to crypto I remember are the already mentioned AES (a sym crypto standard, no public key and much effect of QC there) and SHA-3 (hash function, same here). So, crypto not affected (in a substabtial way, there is some change by Grover's algorithm and so on but nothing 'major'; the double key... – quid Apr 20 '13 at 23:54nowas we are used to using the internet for all kinds of things, not so much. Sure if as of tomorrow these these things would stop working/being secure this would be a problem. However,... – quid Apr 21 '13 at 0:00