[geeks] Interesting: hardware security token for PayPal

[Phil Stracchino]

Dan Duncan wrote:
> On 3/31/07, Phil Stracchino <phil.stracchino at speakeasy.net> wrote:
>> This is an interesting-looking gadget from PayPal:
>>
>> https://www.paypal.com/us/cgi-bin/webscr?cmd=xpt/cps/general/PayPalSecurityKey
>>
>> If the device generates a six-digit code "about every 30 seconds", then
>> it takes it "about a year" to exhaust all possible codes and start over.
> 
> We use RSA SecurID tokens like this at $WORK.  Rumor has it a former
> employee left his at home with a password-protected webcam pointing at it
> so he didn't need to carry it with him.  I don't know if that's why
> he's a former
> employee.  Of course, it's just a rumor.
> 
>> However, the algorithm must necessarily be deterministic, or it wouldn't
>> work.
> 
> I always assumed it was a string of pseudo-random numbers with a
> shared seed.  The number would seem random, but both ends could
> always generate the same number if they knew how many minutes had
> elapsed (mine is in minutes, not half minutes) from some point in time.
> 
> This was always a fun phenomenon to demonstrate to new programming
> students.  :)

I'm told the algorithm is something like this:  The unit takes a 64-bit
current time, a 128-bit random seed, a 32-bit token serial number, and
32 bits of padding.  Pass this 256 bits of data into AES256 in ECB mode,
and then use some proprietary algorithm to select which N digits of the
result to display.



-- 
 It's not the years, it's the mileage.
 Phil Stracchino              phil.stracchino at speakeasy.net
 Renaissance Man, Unix generalist, Perl hacker, Free Stater
 Landline: 603-429-0220                Mobile: 603-320-5438