Where is the credit card number
The Secret Algorithm in Your Credit Card Number
chances are you have a credit card in
your wallet on the front is usually
something like your name and other
information like your bank and the card
carrier like Visa MasterCard etc and a
string of sixteen fifteen or fourteen
numerical digits these digits vary from
card to card and they're enough for
merchants to transact business with your
bank on your behalf
however this string of numbers isn't
random in fact there's a secret code in
there that validates your card and keeps
it safe all in the number structure
it's a low-tech mathematical algorithm
called the loon formula invented by Hans
Peter Luhn in 1954 this mathematical
tool actually dates back to before the
existence of credit cards even with that
fact it's included in every credit debit
an ATM card on earth and it also makes
for a mind-blowing bar trick if people
don't know it here's how you can see how
it works first you'll want to write out
your or any credit card number on a
piece of paper this is a randomly
generated Visa card number so it's not
real you can try but it's not going to
work now once you have that card number
written out you'll double every other
number starting with the second number
from the right and then write them below
that card number like this once you've
done that you'll have a new string of
numbers with every other number doubled
starting from the right after doing that
any two-digit numbers as a result of the
doubling you'll sum both of those
individual numbers together to get a
single number so with our first two
digit number of 16 you'll sum 1 in 6 to
get 7 making a 1 digit number
extrapolating that process out here's
our new string finally at all the
numbers you're left with in the string
doubled and original like below ignoring
the original numbers that you doubled
and now have a new number 4 if your
final sum is divisible by 10 then it's a
valid card number if the final sum isn't
divisible by 10 then the card number
isn't valid or you did something wrong
in the case of our sample number it's
just not in use but it's still a valid
number this algorithm is used to
calculate every single card number on
earth Visa Mastercard Discover they all
have 16 digits and American Express has
15
and then diners club cards have 14 each
different card issuer will have
different subcategories of what numbers
mean in their string like issuer ID
account number etc but they all have to
line up with the lewd algorithm
back to the Loon algorithm itself the
last number in your credit card is
referred to as a check digit as the
computer runs the algorithm it will
complete its sum without the last number
using our sample number as an example
we've replaced the final digit of nine
with an X variable by then completing
the sum were left with a final number of
81 plus X now the computer can look back
at the original number see that the last
digit is in fact nine and when added to
the sum it creates a number divisible by
10 this divisibility by 10 we see in the
Loon algorithm also lends to its
alternative name of modulus 10 or mod 10
the algorithm was originally used to
detect data entry errors and to verify
number strings not as a defense against
fraud however today it functions as a
great first flag for fraud detection
software on credit card issuers internal
systems chances are if the Loon
algorithm doesn't check out there might
be something else at play as well there
are some cases that the Loon algorithm
can't catch so it's not a solve all for
checking credit card numbers but it is
the primary rule that card numbers have
to abide by this algorithm isn't just
used for credit cards either it's also
used in the IMEI cards in cell phones
and commonly in insurance identifier
numbers Ethernet networking also uses a
similar check digit system to ensure
data arrives just like it was sent and
didn't get garbled up along the way
algorithms using Lewton methodology are
seen all across our modern digital
infrastructure and now you can blow some
people's minds at the bar while also
covertly getting their credit card
numbers thanks for watching
you
