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From Costin Manolache <cmanola...@yahoo.com>
Subject Re: Duplicate session IDs are *common*
Date Fri, 10 Jan 2003 19:11:39 GMT
Eric Rescorla wrote:

> Jim Jagielski <jim@jaguNET.com> writes:
> 
>> Eric Rescorla wrote:
>> > 
>> > Glenn Olander <glenn@greenoak.com> writes:
>> > > 5) The strength of the PRNG is largely irrelevant
>> > > 
>> > > As a user, I wouldn't trust any solution which lacks a check for
>> > > duplicate session id's, regardless of the strength of the PRNG.
>> > This doesn't seem to me to be a plausible position in view
>> > of the fact that all of our security mechanisms absolutely
>> > depend on statistical uniqueness of randomly generated large
>> > numbers.
>> > 
>> 
>> These are 2 different points I think. If you randomly generate numbers
>> between 1 and 1,000,000 you will, after a point in time, have
>> duplicate numbers.
> Yes, but if you randomly generate numbers between 1 and 2^128, you'll
> have to generate roughly 2^64 random numbers to have a good chance of
> getting a duplicate. Sure, over time you'll get a duplicate,
> but in this context over time needs to be measured over a
> time scale far in excess of the time scale that is interesting.

Adding the startup time doesn't hurt. 
Or enough bits of the startup time to guarantee a duplicate won't
happen in our life. 

We'll still have the probability that 2 random number generated at the
same time ( same millis ) will be identical.  :-)

Costin






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