LUNH ALGORITHM

LUNH ALGORITHM :

The modulus 10 or mod 10 algorithm, is a simple checksum formula used to validate a variety of identification numbers, such as credit card numbers, IMEI numbers, Canadian Social Insurance Numbers.

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 digit number i.e greater than 9(e.g., 6 × 2 = 12), then add the digits of the product (e.g., 12: 1 + 2 = 3, 15: 1 + 5 = 6), to get a single digit number.

Step 3 - Now take the sum of all the digits.

Step 4 - If the total modulo 10 is equal to 0 (if the total ends in zero) then the number is valid according to the Luhn formula; else it is not valid.

EX :

def checkLuhn(cardNo):

    nDigits = len(cardNo)
    nSum = 0
    isSecond = False

    for i in range(nDigits - 1, -1, -1):
        d = ord(cardNo[i]) - ord('0')

        if (isSecond == True):
            d = d * 2