[TriLUG] OT: RSA Securid - how does it work?

[Joseph Mack NA3T]

I have one of these keys, which gives a different random 
number every minute, so I can logon at work. I'm wondering 
how it keeps synchronisation with the server. Searches on 
google for "RSA Securid how does it work" only come up with 
pages on how to login with it (and shills from RSA telling 
me how wonderful these keys are).

I assume that the key has a free running crystal oscillator 
in which case the setting and long term drift will not be 
better than 1:10^6 and it would go out of synch in 2yrs 
(60*10^6 secs). Mine has a date of Nov 2003 on the back, so 
presumably it's been running for 4 years. Assuming the 
battery will last 10yrs, this would mean that the accuracy 
of the crystal would have to be 1:10^7 to maintain synch 
over this time. This tolerance is a bit tighter than I would 
expect is possible.

Anyone know how these things keep synchronised with the 
server?

Thanks Joe

-- 
Joseph Mack NA3T EME(B,D), FM05lw North Carolina
jmack (at) wm7d (dot) net - azimuthal equidistant map
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