What is a Luhn Check Test?

The Luhn check, also known as the Luhn algorithm, is a simple checksum formula used to validate a variety of identification numbers, including credit card numbers. It is designed to protect against accidental errors, not fraudulent activity.

How to Perform a Luhn Check Test

To test a CVV code with the Luhn algorithm, start by doubling every second digit from the rightmost end. If the result is a two-digit number, add the digits together. Subtract 9 from any total greater than 9. Finally, add all the digits together. If the total modulo 10 is 0, the number is valid.

Why Validate CVV Codes?

Validating CVV codes during transactions adds an extra layer of security, reducing the risk of fraudulent activities. It ensures that the person using the card has physical possession of it.

Example

For instance, consider the CVV code 123. Doubling the second digit from the right gives 2 * 3 = 6. The sum of all digits is 1 + 2 + 3 + 6 = 12. Since 12 modulo 10 is 2, the CVV code 123 is invalid.