Tools to check Luhn generated numbers. The Luhn algorithm (also called modulo 10 or mod 10) is a checksum formula for numbers/digits used with credit card or administrative numbers.

Luhn Number Checksum - dCode

Tag(s) : Checksum, Arithmetics

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Tools to check Luhn generated numbers. The Luhn algorithm (also called modulo 10 or mod 10) is a checksum formula for numbers/digits used with credit card or administrative numbers.

This algorithm allows checking credit card numbers MasterCard/AMEX/Visa of IMEI codes for example by using a control key checksum. If one character is badly written, in the Luhn algorithm can detect it.

Example: 12345674 is a valid card number, 1234567 is the main original number and 4 is the checksum.

Example: If a user enter 13245674 (2 and 3 are switched), then the program calculates the checksum for 1324567 and finds 5 instead of 4 expected, the number is invalid and so has been badly typed.

The algorithm starts by the end of the number, from the last right digit to the first left digit. Realize a sum of digits by multiplying by 2 all digits of even rank. If the double is equal or superior to 10, replace it by the sum of its digits. The control digit number is equal to (10-sum%10) % 10.

Example: The number 853X, with X=0, the digit to calculate.

Take the digit 3, doubled, 3*2 = 6.

Takes the digit 5, not multiplied by 2

Take the 8, multiplies it by 2 : 8*2=16 and 1+6=7 to get 7.

The sum is 6+5+7 = 18. As 18 modulo 10 = 8, one calculated (10 - 8) %10 = 2, 2 is the digit checksum control. So 8532 is valid according to Luhn.

These codes are generated by the banks, Visa and MasterCard have their own algorithm (based on private key) using the personal account number, the expiry date of the card and the service code, this information is then compared by those calculated by the bank. These numbers are therefore impossible to compute without knowing the private key, and there is no relation to Luhn's algorithm.

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