Bruno Wolff III <bruno@xxxxxxxx> writes: > On Tue, Feb 07, 2006 at 15:28:31 +0300, > Nikolay Samokhvalov <samokhvalov@xxxxxxxxx> wrote: >> The real situation would be as the following. >> I want to use some algorithm to hide real number of registered users >> in my table user. So, I don't want to use simple sequence, when every >> new registered user in my system can guess what is the number of >> registered users simply observing his ID. So, I use following > (N and M are said to be "relatively prime".) > > The above method isn't very secure. You might be better off using a block > cipher in counter mode, depending on how badly you want to keep the number > of users secret. Even that won't be foolproof as the users might cooperate > with each other to estimate how many of them there are. Or, just start your sequence counting at 1000000. Or use bigint and start it at a billion. -Doug
