check any credit card valid!!!
 11.25.2009, 6:51 PM 
Before we understand how credit card numbers are generated, here is a
brief explanation of what a typical credit card number means.
* Out of the 16 numbers on a typical credit card, the set of first 6
digits is known as the issuer identifier number (read this for
details), and the last digit is known as the ?check digit? which is
generated in such a way as to satisfy a certain condition (the Luhn or
Mod 10 check). ?Luhn check? is explained later in this post. The term
sounds intimidating, but it?s really a very simple (and elegant)
concept.
* Taking away the 6 identifier digits and 1 check digit leaves us with 9 digits in the middle that form the ?account number?.
* Now, there are 10 possible numbers (from 0 to 9) that can be arranged
in these 9 places. This gives rise to 109 combinations, that is, 1
billion possible account numbers (per issuer identifier).
* With each account number, there is always an unique check digit
associated (for a given issuer identifier and an account number, there
cannot be more than one correct check digit)
* Amex issues credit cards with15 digits. The account numbers in this case are 8 digit long.
What is the ?Luhn? or ?Mod 10″ check?
In 1954, Hans Luhn of IBM proposed an algorithm to be used as a
validity criterion for a given set of numbers. Almost all credit card
numbers are generated following this validity criterion?also called as
the Luhn check or the Mod 10 check. It goes without saying that the
Luhn check is also used to verify a given existing card number. If a
credit card number does not satisfy this check, it is not a valid
number. For a 16 digit credit card number, the Luhn check can be
described as follows:
1. Starting with the check digit, double the value of every second
digit (never double the check digit). For example, in a 16 digit credit
card number, double the 15th, 13th, 11th, 9th?digits (digits in odd
places). In all, you will need to double eight digits.
2. If doubling of a number results in a two digit number, add up the
digits to get a single digit number. This will result in eight single
digit numbers.
3. Now, replace the digits in the odd places (in the original credit
card number) with these new single digit numbers to get a new 16 digit
number.
4. Add up all the digits in this new number. If the final total is
perfectly divisible by 10, then the credit card number is valid (Luhn
check is satisfied), else it is invalid.
When credit card numbers are generated, the same steps are followed
with one minor change. First, the issuer identifier and account numbers
are assigned (issuer numbers are fixed for a given financial
institution, whereas the account numbers are randomly allocated  I
think). Then, the check digit is assumed to be some variable, say X.
After this, the above steps are followed, and during the last step, X
is chosen in such a way that it satisfies the Luhn check.
This part is a bit confusing and takes some time to understand.
However, don?t get stuck here?continue reading through the examples
below and you will figure out what this is all about.
Credit card numbers valid or invalid?
Have you ever wondered if those numbers on the fake plastic or
cardboard credit cards that come with the ?preapproved? offers are real
or imaginary? If they are not valid, how do you know it??Just apply the
Luhn check and all the those fake credit cards will invariably
fail.Here is an example of a VISA credit card (look at the expiry date
 01/09 ..it?s still valid ! ;) )
Note that the credit card number starts with ?4″?so it is indeed a VISA issued credit card (VISA cards
start with ?4″ and MasterCard/Maestro cards start with ?5″). Now, let
us apply the Luhn algorithm to this card. To make it easier on you
guys, I have created a schematic of the steps towards the Luhn check
(below) for this card number 4552 7204 1234 5678:
* In this case, when we sum up the total, it comes to 61 which is not
perfectly divisible by 10, and hence this credit card number is invalid.
* If such a credit card number is ever generated, the value of the
check digit would be adjusted in such a way as to satisfy the Luhn
condition. In this case, the only value of the check digit, that will
create a valid credit card number, is 7. Choosing 7 as the check digit
will bring the total to 60 (which is perfectly divisible by 10) and the
Luhn condition will be satisfied. So the valid credit card number will
be 4552 7204 1234 5677.
Let?s try another example, this time with a MasterCard.
Again, performing the Luhn check on this credit card number, we have:
* The total comes to 65 which is not perfectly divisible by 10. Hence this credit card number is invalid.
* In this case, a valid credit card number will result only if the
check digit is 8. This will bring the total to 70 which is perfectly
divisible by 10. So the valid credit card number will be 5490 1234 5678
9128.
Closing remarks
If I still have your attention, here are some additional thoughts. In
the context of this post, by the term ?valid?, I mean ?mathematically
valid?. A mathematically valid credit card does not mean a ?working?
credit card. The Luhn formula validates only the credit card number; it
does not validate the expiry date and/or card security code (CVV, CVC).
Plus, as discussed before, the 9 digit account number will yield 1
billion combinations; so the chances of getting a working credit card
number are very remote. It should also be noted that, this validation
is usually employed at the transaction end; which means that numbers
that do not satisfy the Luhn check are not forwarded to the card issuer
and the transaction is terminated. If you have a fake credit card which
satisfies the Luhn check, it will go through at the transaction end,
but the card issuer will most likely catch the mischief. So don?t go
about trying to use these numbers to buy stuff.
Just to be clear on this, I don?t expect comments like these (check out the source of this comment):
hey. im hearing good things about your site! i need some money to jump
start my poker career. Probably about 40100$ would do. i dont have a
credit card to use and it pisses me off because i know i could beat the
majority of the people online. please help
If you intend to post such comments, at least be extremely funny. :)
So you think you can separate out valid and invalid account numbers now? Here are a couple of trial numbers for you:
* 5491 9469 1544 4923  Valid or invalid? If invalid, what should have been the correct check digit to make it valid?
* 4539 9920 4349 1562  Valid or invalid? If invalid, what should have been the correct check digit to make it valid?
Sudoku fans will quickly figure out multiple valid combinations of the
above numbers. If you don?t want to do the math, here are some ready
made valid (?test?) credit card numbers from Paypal.By the way, the
Luhn check is also valid for debit card numbers.I am still in the
learning phase with this topic and trying to further understand how
people use (or misuse (?)) such information. If you have some insight
in this matter, please feel free to share it with us.If you liked what
you read above, go ahead and subscribe to this blog to get more
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Resources and References
There is a vast amount of literature on the Luhn algorithm and a quick
Google search will enlighten you on how popular this topic is. If you
don?t want to read all that, here are links to some interesting reading. 
Category: Hacking tutorials  Added by: h4ckz0r

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