Abstract: Various embodiments of the teachings herein include methods for determining a Gaussian integer congruent to a given Gaussian integer modulo. The method may include: starting with a Gaussian integer base raised to an integer exponent having a norm smaller than or equal to that of the Gaussian integer modulus and larger than the norm of the difference of the Gaussian integer base raised to the integer exponent and the Gaussian n integer modulus; initializing a variable value candidate for the Gaussian integer congruent with the given Gaussian integer; then iteratively decrementing the variable value by a product of the Gaussian integer modulus and a component-wise down rounded quotient of the current value of the variable value candidate and the Gaussian integer base raised to the integer exponent, as long as the quotient is not vanishing; and identifying the resulting variable value candidate as the Gaussian integer congruent.

Abstract: Various embodiments of the teachings herein include a method for onboarding an IoT device (3) of a manufacturer, in a manner secure against quantum computer attacks, in an infrastructure of a customer by means of a first server (1) of a manufacturer domain of the manufacturer and a second server (2) of a customer domain of the customer. In some embodiments, three authenticated and encrypted communication channels and a key encapsulation method are used to provide a device certificate of the customer domain for the IoT device on the IoT device.