Asp Forum - [QUIZ] Checking Credit Cards (#122

James Gray

4/27/2007 12:00:00 PM

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on Ruby Talk follow the discussion. Please reply to the original quiz message,
if you can.

-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

Before a credit card is submitted to a financial institution, it generally makes
sense to run some simple reality checks on the number. The numbers are a good
length and it's common to make minor transcription errors when the card is not
scanned directly.

The first check people often do is to validate that the card matches a known
pattern from one of the accepted card providers. Some of these patterns are:

+============+=============+===============+
| Card Type | Begins With | Number Length |
+============+=============+===============+
| AMEX | 34 or 37 | 15 |
+------------+-------------+---------------+
| Discover | 6011 | 16 |
+------------+-------------+---------------+
| MasterCard | 51-55 | 16 |
+------------+-------------+---------------+
| Visa | 4 | 13 or 16 |
+------------+-------------+---------------+

All of these card types also generate numbers such that they can be validated by
the Luhn algorithm, so that's the second check systems usually try. The steps
are:

1. Starting with the next to last digit and continuing with every other
digit going back to the beginning of the card, double the digit
2. Sum all doubled and untouched digits in the number
3. If that total is a multiple of 10, the number is valid

For example, given the card number 4408 0412 3456 7893:

Step 1: 8 4 0 8 0 4 2 2 6 4 10 6 14 8 18 3
Step 2: 8+4+0+8+0+4+2+2+6+4+1+0+6+1+4+8+1+8+3 = 70
Step 3: 70 % 10 == 0

Thus that card is valid.

Let's try one more, 4417 1234 5678 9112:

Step 1: 8 4 2 7 2 2 6 4 10 6 14 8 18 1 2 2
Step 2: 8+4+2+7+2+2+6+4+1+0+6+1+4+8+1+8+1+2+2 = 69
Step 3: 69 % 10 != 0

That card is not valid.

This week's Ruby Quiz is to write a program that accepts a credit card number as
a command-line argument. The program should print the card's type (or Unknown)
as well a Valid/Invalid indication of whether or not the card passes the Luhn
algorithm.

60 Answers

John Joyce

4/27/2007 12:11:00 PM

On Apr 27, 2007, at 8:59 PM, Ruby Quiz wrote:

> The three rules of Ruby Quiz:
>
> 1. Please do not post any solutions or spoiler discussion for this
> quiz until
> 48 hours have passed from the time on this message.
>
> 2. Support Ruby Quiz by submitting ideas as often as you can:
>
> http://www.rub...
>
> 3. Enjoy!
>
> Suggestion: A [QUIZ] in the subject of emails about the problem
> helps everyone
> on Ruby Talk follow the discussion. Please reply to the original
> quiz message,
> if you can.
>
> -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
> =-=-=-=-=-=-=
>
> Before a credit card is submitted to a financial institution, it
> generally makes
> sense to run some simple reality checks on the number. The numbers
> are a good
> length and it's common to make minor transcription errors when the
> card is not
> scanned directly.
>
> The first check people often do is to validate that the card
> matches a known
> pattern from one of the accepted card providers. Some of these
> patterns are:
>
> +============+=============+===============+
> | Card Type | Begins With | Number Length |
> +============+=============+===============+
> | AMEX | 34 or 37 | 15 |
> +------------+-------------+---------------+
> | Discover | 6011 | 16 |
> +------------+-------------+---------------+
> | MasterCard | 51-55 | 16 |
> +------------+-------------+---------------+
> | Visa | 4 | 13 or 16 |
> +------------+-------------+---------------+
>
> All of these card types also generate numbers such that they can be
> validated by
> the Luhn algorithm, so that's the second check systems usually
> try. The steps
> are:
>
> 1. Starting with the next to last digit and continuing with every
> other
> digit going back to the beginning of the card, double the digit
> 2. Sum all doubled and untouched digits in the number
> 3. If that total is a multiple of 10, the number is valid
>
> For example, given the card number 4408 0412 3456 7893:
>
> Step 1: 8 4 0 8 0 4 2 2 6 4 10 6 14 8 18 3
> Step 2: 8+4+0+8+0+4+2+2+6+4+1+0+6+1+4+8+1+8+3 = 70
> Step 3: 70 % 10 == 0
>
> Thus that card is valid.
>
> Let's try one more, 4417 1234 5678 9112:
>
> Step 1: 8 4 2 7 2 2 6 4 10 6 14 8 18 1 2 2
> Step 2: 8+4+2+7+2+2+6+4+1+0+6+1+4+8+1+8+1+2+2 = 69
> Step 3: 69 % 10 != 0
>
> That card is not valid.
>
> This week's Ruby Quiz is to write a program that accepts a credit
> card number as
> a command-line argument. The program should print the card's type
> (or Unknown)
> as well a Valid/Invalid indication of whether or not the card
> passes the Luhn
> algorithm.
>

For completeness and to make this Quiz exercise valid to more people,
can anyone include the information for other major credit cards from
major countries? Japan: JCB, et. al., U.K.: Barclay, et. al. , etc...
This would be good to expand the exercise and return more to our
friends in various areas!
Discover is itself not found outside of North America, AFIK.

Tim Becker

4/27/2007 12:22:00 PM

> For completeness and to make this Quiz exercise valid to more people,
> can anyone include the information for other major credit cards from
> major countries? Japan: JCB, et. al., U.K.: Barclay, et. al. , etc...

UK had Switch and Solo till recently which are now rebranded under the
Maestro umbrella. They're not really credit cards and basically no
rules exist, you have to check tables to determine valid prefixes and
card number length. Additionally, Maestro card numbers may also be
Mastercard numbers, so they can't be uniquely identified as being
Maestro.

For JCB and Diner's:

JCB 3528-2589 Length: 16
Diners 3000-3029, 3040-3059, 36, 3815-3889, 389 Length: 14

Cheers,
-Tim

Daniel Martin

4/27/2007 12:36:00 PM

Ruby Quiz <james@grayproductions.net> writes:

> This week's Ruby Quiz is to write a program that accepts a credit
> card number as a command-line argument. The program should print
> the card's type (or Unknown) as well a Valid/Invalid indication of
> whether or not the card passes the Luhn algorithm.

May I make an additional suggestion? Treat spaces in the card number
as perfectly valid, and simply strip them before processing. One of
the most irritating features found in many online stores is the
requirement that the credit card number be typed in with no spaces.
(The other biggie is using a select box for the state abbreviation)

Now granted, for accepting the card number from the command line this
will mean that on the command line the card number was quoted, but
presumably most people's programs will be a command-line wrapper
around a function/class that does the real work.

--
s=%q( Daniel Martin -- martin@snowplow.org
puts "s=%q(#{s})",s.to_a[1] )
puts "s=%q(#{s})",s.to_a[1]

James Gray

4/27/2007 12:54:00 PM

On Apr 27, 2007, at 7:36 AM, Daniel Martin wrote:

> Now granted, for accepting the card number from the command line this
> will mean that on the command line the card number was quoted...

It doesn't have to mean that:

$ ruby -e 'p ARGV.join' 1111 2222 3333 4444
"1111222233334444"

James Edward Gray II

John Joyce

4/27/2007 1:11:00 PM

On Apr 27, 2007, at 9:22 PM, Tim Becker wrote:

>> For completeness and to make this Quiz exercise valid to more people,
>> can anyone include the information for other major credit cards from
>> major countries? Japan: JCB, et. al., U.K.: Barclay, et. al. ,
>> etc...
>
> UK had Switch and Solo till recently which are now rebranded under the
> Maestro umbrella. They're not really credit cards and basically no
> rules exist, you have to check tables to determine valid prefixes and
> card number length. Additionally, Maestro card numbers may also be
> Mastercard numbers, so they can't be uniquely identified as being
> Maestro.
>
> For JCB and Diner's:
>
> JCB 3528-2589 Length: 16
> Diners 3000-3029, 3040-3059, 36, 3815-3889, 389 Length: 14
>
>
> Cheers,
> -Tim
>
Wow, those are some broad ranges.

Tim Becker

4/27/2007 1:37:00 PM

> > JCB 3528-2589 Length: 16

should be 3528-3589, obviously.

> > Diners 3000-3029, 3040-3059, 36, 3815-3889, 389 Length: 14

> Wow, those are some broad ranges.

Well, those ranges DO include Carte Blanche :) I haven't seen a
physical Diners Card in at least 20 years to be honest, not sure who
still uses them.

If you think those ranges are broad, the last UK-Switch/Solo table I
had has over 180 card prefixes with different card lengths...

John Joyce

4/27/2007 2:15:00 PM

On Apr 27, 2007, at 10:37 PM, Tim Becker wrote:

>> > JCB 3528-2589 Length: 16
>
> should be 3528-3589, obviously.
>
>> > Diners 3000-3029, 3040-3059, 36, 3815-3889, 389 Length: 14
>
>> Wow, those are some broad ranges.
>
> Well, those ranges DO include Carte Blanche :) I haven't seen a
> physical Diners Card in at least 20 years to be honest, not sure who
> still uses them.
>
> If you think those ranges are broad, the last UK-Switch/Solo table I
> had has over 180 card prefixes with different card lengths...
>
My grandmother used to have a Diners Club card. Last time I saw that
was about 20 years ago too.
But of the cards accepted here in Tokyo, Diners Club is one that is
often listed! (in bars and restaurants of course)

Oh, I can only imagine. Processing cards with less deeply thought out
numbering schemes. The big boys planned that stuff back when
computing power was a premium.

matthew.moss.coder

4/27/2007 5:59:00 PM

> +============+=============+===============+
> | Card Type | Begins With | Number Length |
> +============+=============+===============+
> | AMEX | 34 or 37 | 15 |
> +------------+-------------+---------------+
> | Discover | 6011 | 16 |
> +------------+-------------+---------------+
> | MasterCard | 51-55 | 16 |
> +------------+-------------+---------------+
> | Visa | 4 | 13 or 16 |
> +------------+-------------+---------------+

So is a card number like "4012 3456 7890" a valid Unknown, or an invalid Visa?
Similarly, for Unknown, should we accept any length, or go for the common 16?

James Gray

4/27/2007 6:20:00 PM

On Apr 27, 2007, at 12:58 PM, Matthew Moss wrote:

>> +============+=============+===============+
>> | Card Type | Begins With | Number Length |
>> +============+=============+===============+
>> | AMEX | 34 or 37 | 15 |
>> +------------+-------------+---------------+
>> | Discover | 6011 | 16 |
>> +------------+-------------+---------------+
>> | MasterCard | 51-55 | 16 |
>> +------------+-------------+---------------+
>> | Visa | 4 | 13 or 16 |
>> +------------+-------------+---------------+
>
> So is a card number like "4012 3456 7890" a valid Unknown, or an
> invalid Visa?

Visa Invalid

Always match the type first.

> Similarly, for Unknown, should we accept any length, or go for the
> common 16?

Unknown is for any type that doesn't match, so it could be any length.

James Edward Gray II

matthew.moss.coder

4/27/2007 7:32:00 PM

So I took this as an opportunity to try doing a little TDD, something
which is appealing but I've never really tried. It _is_ fun to see
failure first and then fix. =) There are probably other tests I
could have included, but here is a start, in case people want to check
a few numbers or add more tests:

Obviously, you may need to change this to match your solution...

require "test/unit"
require "ccard"

class CreditCardCheckTest < Test::Unit::TestCase

def test_valid_numbers
assert CreditCard.new("4408041234567893").valid?
assert CreditCard.new("6011111111111117").valid?
end

def test_invalid_nubers
assert !CreditCard.new("4417123456789112").valid?
end

def test_valid_numbers_with_spaces
assert CreditCard.new("4408 0412 3456 7893").valid?
assert CreditCard.new("6011 1111 1111 1117").valid?
end

def test_invalid_nubers_with_spaces
assert !CreditCard.new("4417 1234 5678 9112").valid?
end

def test_valid_types
assert_equal CreditCard.new("4408041234567893").type, :visa
assert_equal CreditCard.new("4408 0412 3456 7893").type, :visa
assert_equal CreditCard.new("6011 1111 1111 1117").type, :discover
assert_equal CreditCard.new("123456789").type, :unknown
end

def test_invalid_types
assert_nil CreditCard.new("4408 0412 3456 789").type
end

end

comp.lang.ruby

[QUIZ] Checking Credit Cards (#122

James Gray

John Joyce

Tim Becker

Daniel Martin

James Gray

John Joyce

Tim Becker

John Joyce

matthew.moss.coder

James Gray

matthew.moss.coder

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