This package is an implementation of the Luhn ModN check. The Luhn algoritm is a numeric checksum formula used to validate credit card numbers etc. The ModN addition allows the validation of a combination of letters and numbers.
The CoronaCheck app uses this check to validate tokens from Covid 19 Test providers. It uses a reduced set of characters to prevent misinterpretation of a 1 vs L vs I, 0 vs O etc.
You can easily check if a provided token passes the luhn ModN check for a given alphabet:
import nl.rijksoverheid.rdo.modules.luhncheck
val tokenValidator = TokenValidatorImpl()
tokenValidator.validate("2SX4XLGGXUB6V9", "42") // true
tokenValidator.validate("YL8BSX9T6J39C7", "L2") // false (invalid token)
License is released under the EUPL 1.2 license. See LICENSE for details.