Comment by bookstore-romeo
1 year ago
My card doesn't even let me include repeating digits in its PIN. I suppose it can make a one-off guess more likely than one in a thousand to correctly guess my PIN.
1 year ago
My card doesn't even let me include repeating digits in its PIN. I suppose it can make a one-off guess more likely than one in a thousand to correctly guess my PIN.
Is it repeating in the whole PIN, or in digits next to each other? I'm trying to resist the nerd snipe of what the total number of possibilities would be in the latter case...
I believe it would be 7290, or more generalized, S(N) = 10 * 9 ^(N-1) with N being the length of the code and S being the number of combinations (assuming that a decimal system is used)
And from there, with variable lengths ranging from L to H, S(L, H) = 5/4 * 9 ^(L-1) * (9^(U-L+1) - 1)
So if the bank allows combinations from 4 - 6 digits, there would be a total of 663390 combinations to choose from.
Now, of course, the bank may decide to go from decimal to hexadecimal in the future - or maybe, there systems allow only duodecimal. In any case, the formula can be generalized further to account for all number systems - with B being the base of the system:
S(L, H, B) = (B/(B-2)) * (B-1) ^(L-1) * ((B-1)^(U-L+1) - 1)
This is only defined for B > 2 - in binary system, there's only ever two combinations which fit the constraint
Which is honestly not a bad idea, given that somebody shoulder surfing or trying to read smudges on the PIN pad becomes much easier in the case of repeated numbers.
"1111" would just leave a fingerprint on a single key, for example, and only one possible PIN (or maybe 3, if the bank/card allows 6 digit PINs).