tag:blogger.com,1999:blog-8883034.post116058748872776077..comments2024-03-23T23:26:40.813+01:00Comments on atdotde: Cheap quantum cryptographyRoberthttp://www.blogger.com/profile/06634377111195468947noreply@blogger.comBlogger4125tag:blogger.com,1999:blog-8883034.post-8196543813296465572013-12-25T10:17:20.793+01:002013-12-25T10:17:20.793+01:00This is really difficult to learn and study. After...This is really difficult to learn and study. After reading so many blog posts I am still not clear with the complete idea behind it. <br /><a href="http://www.arx.com" rel="nofollow">e signatures</a>Anonymoushttps://www.blogger.com/profile/08668675991465015224noreply@blogger.comtag:blogger.com,1999:blog-8883034.post-1160901152458434802006-10-15T10:32:00.000+02:002006-10-15T10:32:00.000+02:00From your link to wikipedia:"Shor's algorithm is a...From your link to wikipedia:<BR/>"Shor's algorithm is a quantum algorithm for factoring a number N in O((log N)^3) time", that is the time needed to factoring a number N grows as the cube of the number of its digits.<BR/><BR/>So if the speed up of the Shor's algorithm were a square root then this would imply that classical algorithms factorize a number N in a time that grows like O((log N)^6), but in the same article of wikipedia: "no classical algorithm is known that can factor in time O((log N)^k) for any k".<BR/><BR/>So the speed up of Shor's algorithm is exponential.<BR/><BR/>On the other hand I think that quantum cryptography is better than your idea of sealed hard discs. With quantum cryptography we have total control of the key from the moment in which it is generated, whereas with sealed hard discs we have to trust many intermediate people.<BR/><BR/>Finally I am not in agreement with your affirmation about quantum information theory: "...all this, much like string theory, is only theory and does not have real world applications"<BR/><BR/>Quantum information theory is not a physical theory, it is the application of quantum mechanics to data processing, and quantum mechanics is a physical theory thoroughly tested. If today we cannot construct a quantum computer it is because the technical difficulties are enormous but not because the quantum mechanics is wrong or because it is a theory without experimental support.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-8883034.post-1160646830609966642006-10-12T11:53:00.000+02:002006-10-12T11:53:00.000+02:00I stand corrected.Regarding copying the key: That'...I <A HREF="http://en.wikipedia.org/wiki/Shor%27s_algorithm" REL="nofollow">stand</A> <A HREF="http://en.wikipedia.org/wiki/Grover%27s_algorithm" REL="nofollow">corrected</A>.<BR/><BR/>Regarding copying the key: That's why I mentioned to "seal" the hard disk. Even in the quantum version, eventually the RSA keys have to be extracted in classical form and then are prone to copying. For practical purposes I thing it would be possible to take a hard disk from Bremen to New York say knowing that nobody had access to the data on it.Roberthttps://www.blogger.com/profile/06634377111195468947noreply@blogger.comtag:blogger.com,1999:blog-8883034.post-1160641958810003672006-10-12T10:32:00.000+02:002006-10-12T10:32:00.000+02:00"A famous example being Shor's algorithm for the f..."A famous example being Shor's algorithm for the factorisation of integers relevant for breaking many popular public key encryption schemes such as RSA. The speed up is not exponential but "only" by a square root but this can already be substantial."<BR/><BR/>The speed up of Shor's algorithm is exponential, the square root speed up is that of Grover's algorithm.<BR/><BR/>Quantum cryptography is the generation of one-time pads between emitter and receiver, the superiority of this scheme on classical one-time pads is that in the classical case the key could have been copied without your knowledge.Anonymousnoreply@blogger.com