Friday, 17 January 2014

number theory - Efficiently determining if a discrete log exists

Finding a discrete log in a finite cyclic group, like (ZN)x, seems hard and in some cases a solution may not even exist. Consider N=15 and the generator function 2k=mmod15. This will produce the following values for m given any non negative integer k...



1,2,4,8,1,



Therefor, the equation 2k=3mod15 would have no (real?) solution. Is there a "fast" way of determining if any solution exists without factoring N?

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