

The Number Code. Crack It If You Can? - rukshn
http://crashzone.tumblr.com/post/41277684058/the-number-code

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tompko
If there are 11 digits that change then there are 10 __11 possible different
numbers. Depending on how many they use per day that give a different amount
of time before they have to repeat:

1000 per day: 273791 years

1000000 per day: 273 years

So even assuming a lot more than your thousands of cards a day they've got a
while before they run out of numbers. Depending on how their system works
trying to guess one is futile, if the cards come into use when they're printed
and are no longer valid once they've been used you've got a very small window
in which to guess one in one hundred billion. So:

1). One hundred billion

2). Tiny to very tiny depending on how many cards are in circulation at any
one time.

3). See above

4). Almost certainly not

5). That depends on how they pick their numbers, if it were me I'd use a
CSPRNG to generate the numbers and store them, this has the advantage that
it's nearly impossible to guess future numbers given previous ones. If they're
only using a PRNG or some other weak system then it may be possible if you
collect a large enough number of cards to predict future numbers.

