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Credit Card Number Validation

  • Most credit card number and Account numbers can be validated using the Luhn algorithm.

  • And many government identification numbers use the algorithm as a simple method of distinguishing valid numbers from mistyped or otherwise incorrect numbers.

WHAT IS LUHN ALGORITHM ?

  • It is a simple checksum formula used to validate a variety of identification numbers such as:

  • Credit Card Numbers.

  • Debit Card Number.

  • Bank Account Numbers.

  • IMEI Numbers.

  • Canadian Social Insurance Numbers.

  • Also known as the modulus 10 or mod 10 algorithm.

  • It was created by IBM scientist Hans Peter Luhn.

  • It was designed to protect against accidental errors, not malicious attacks.

HOW IT WORKS ?

  • Let’s understand the algorithm with an example.

Credit card

SPS Bank

4 0 1 2   8 8 8 8   8 8 8 8   1 8 8 1  

08/25

VALID

THRU

Birendra Pradhan

1

Major Industry Identifier (MII)  (eg. Banking, Airline, Travel)

1st digit :

2

Issuer Identification Number (eg. Visa, MasterCard, Amex)

1st - 6th digits :

3

Account Number 

7th onward :

(excluding last digit)

4

Check Digits

Last digit :

1
2
3
4

  • Here are the Luhn steps which can used to validate the credit card number :

4000077358283885

Step 1 : Starting from the rightmost digit double the value of every second digit.

Step 2 : 

If doubling of a number results in a two digits number i.e greater than 9 (e.g., 8 × 2 = 16), add up the two digits to get a single-digit number (like for 16:1+6, 18=1+8).

Step 3 : 

Now add the un-doubled digits to the odd places.

Step 4 : 

Now take the sum of all the digits.

Step 5 : 

If the result from Step 4 is divisible by 10, the card number is valid; otherwise, it is invalid.

Double every other

(Right to left)

Add up the two digits 

4  0  0  0  0  7  7  3  5  8  2  8  3  8  8  5

Drop the last digit.

(4x2)

(0x2)

(0x2)

(7x2)

(5x2)

(2x2)

(3x2)

(8x2)

8      0      0     14    10     4      6     16  

(1+4)

(1+0)

(1+6)

8      0      0      5      1      4      6      7  

(if any result higher than 9)

Add un-doubled digits

8  0  0  0  0  7  5  3  1  8  4  8  6  8  7  5

Sum of all nos. together

8+0+0+0+0+7+5+3+1+8+4+8+6+8+7+5  = 70

Molulo 10

(if result is 0, valid; otherwise invalid)

70 modulo 10 = 0

The card number is valid.

  • This algorithm also apply on :

  • Account numbers. 

  • IMEI numbers.

  • Canadian Social Insurance Numbers.

WHY LUHN ALGORITHM ?

  • The Luhn algorithm detects any single-digit error, as well as almost all transpositions of adjacent digits.

  • When you implementing eCommerce application, It is a best practice validating credit card number before send it to the bank validation.

WEAKNESS

  •  It will not detect transposition of the two-digit sequence 09 to 90 (or vice versa).

  • It will detect 7 of the 10 possible twin errors (it will not detect 22 ↔ 55, 33 ↔ 66 or 44 ↔ 77).

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