Luhnkoodi

Luhnkoodi, also known as the Luhn algorithm or Luhn formula, is a simple checksum formula used to validate a variety of identification numbers, such as credit card numbers, IMEI numbers, and National Provider Identifier numbers. It was created by IBM scientist Hans Peter Luhn in 1954. The algorithm works by processing each digit of the number in a specific manner and then checking the sum of the processed digits against a modulus. If the total modulo 10 equals 0, then the number is valid according to the Luhn formula.

The Luhn algorithm is particularly useful in detecting errors in data entry, such as typos or transpositions. It does not, however, provide any information about the validity of the number beyond its internal consistency. For example, it does not check whether a credit card number actually belongs to a valid cardholder.

The algorithm works as follows: starting from the rightmost digit (which is the check digit), double the value of every second digit. If doubling a number results in a number greater than 9, then add the digits of the product (or alternatively, subtract 9 from the product). The sum of all the digits, including the check digit, should be divisible by 10. If it is, then the number is valid according to the Luhn algorithm.

Luhnkoodi is widely used in various industries due to its simplicity and effectiveness in error detection. However, it is not foolproof and can be bypassed with more sophisticated methods. Despite this, it remains a valuable tool in data validation and error detection.