Drakensnyheter 2007-09-14

Nu har två oberoende av varandra forskarlag byggt kvantdatorer som kan faktorisera stora primtal. Det betyder slutet för kryptering som vi känner till den!

(tags: computer Security)

Diskussionen om hur oroliga vi skall vara och vad det här får för praktisk betydelse har gått höga på Slashdot. Vi publiserar några av de mer sansade kommentarerna.

·        The quantum computer referenced in the summary managed the immense feat of finding the factors of the number 15. While it is true that factoring numbers of the magnitude used in cryptography is now a ”matter of engineering”, there are profound difficulties involved in scaling quantum computing. The fundamental problem is called ”decoherence” and describes the tendency of quantum systems to become entangled with their environment, and the consequent loss of pure quantum states. The issues involved in quantum computation connect to deep issues of thermodynamics and entropy, and research on quantum computation has potentially great significance for fundamental physics. Cryptography may have to develop and implement new, extended standards as computational techniques evolve, but the encryption sky is not yet falling.

 ·       It doesn’t necessarily mean the end of public key cryptography, it just means we’ll have to come up with something other than prime factoring to compute the keys.What this does mean is that there’s going to be a lot of money to be made replacing public-key cryptograhy in custom code ala Y2K.  

·        Factoring a four-bit number on a quantum computer requires quite a lot of qbits. You require 20 qbits just to store a four-bit number, and more just to execute the algorithm. This is a big improvement on the few-qbit machines previously made. At this point, while decoherence is still a large barrier, it’s solely an engineering barrier, and one should expect it to last for too long. (Where ”too long” is in physics terms. You’ll probably be okay for 20 years or so.)