Nordic Semiconductor ASA
PROTECTING CRYPTOGRAPHIC KEY DATA

Abstract:

A cryptographic module is switchable between a key-input mode and a data-input mode. In the key-input mode, the cryptographic module receives key data, key length information and first input data, combines an amount of the key data corresponding to the key length information with the first input data to produce combined data, wherein a key-influenced length of the combined data is the shortest length of the combined data that contains every data bit of the combined data whose value depends on the key data. It performs a cryptographic operation on the combined data to generate first output data and does not output any of the first output data until after the cryptographic operation has been applied to all of the key-influenced length of the combined data. In the data-input mode of operation, the cryptographic module receives a quantity of second input data whose length can be less than said key-influenced length, performs the cryptographic operation on the second input data to generate second output data and outputs the second output data.