Bruno Wolff III <bruno@wolff.to> writes:
> On Tue, Feb 07, 2006 at 15:28:31 +0300,
> Nikolay Samokhvalov <samokhvalov@gmail.com> 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
