CCheck

Description:

Ruby credit cards checker using the Luhn algorithm.

Problem

Before submitting a credit card to a payment gateway it's important that we run some sanity checks on the number.

A common check that is performed upfront is to validate the card type based on the starting digits and length of card number. The main patterns that we care about are as follows:

+============+=============+===============+
| 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:

Starting with the next to last digit and continuing with every other digit going back to the beginning of the card, double the digit
Sum all doubled and untouched digits in the number. For digits greater than 9 you will need to split them and sum the independently (i.e. "10", 1 + 0).
If that total is a multiple of 10, the number is valid.

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

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

Thus that card is valid.

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

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

This card is not valid.

Features

Card numbers can be passed in line by line (one set of numbers per line). The program will print the card in the following format:

TYPE: NUMBERS (VALIDITY)

Input and Output

Given the following credit cards:

4111111111111111
4111111111111
4012888888881881
378282246310005
6011111111111117
5105105105105100
5105 1051 0510 5106
9111111111111111

It will output the following:

VISA: 4111111111111111       (valid)
VISA: 4111111111111          (invalid)
VISA: 4012888888881881       (valid)
AMEX: 378282246310005        (valid)
Discover: 6011111111111117   (valid)
MasterCard: 5105105105105100 (valid)
MasterCard: 5105105105105106 (invalid)
Unknown: 9111111111111111    (invalid)

Installation:

With RubyGems, open a terminal and type:

$ {sudo} gem install ccheck

Local installation:

$ git clone [email protected]:jpablobr/ccheck.git

then:

$ cd ccheck
$ rake install

or with bundler

$ cd ccheck
$ bundle build
$ bundle install

Command line Usage:

-h   --help", "Print this help."
-v   --version", "Print version."

examples:

$ ccheck 4111111111111111
$ ccheck 4111111111111111 9111111111111111 '5105 1051 0510 5106' 
$ cat cards-stdin.txt | while read card; do ccheck $card; done

Note: Remember to take account of native $SHELL expansion. Proper character escaping and the like is required.

Running Tests

$ cd ccheck
$ rake

Caveats

ruby 1.9.3 is required (see .rvmrc file).