A mobile terminal for use in a mobile communications system includes a SIM card storing subscriber related data. For security, the SIM card performs secret cryptographic calculations with secret numbers. Secret information is hidden from outside observation by scheduling the calculations using a precomputed, fixed randomization schedule in such a way that externally observable parameters of the device cannot be associated to particular pieces, bits, symbols or values of the secret information.
A secured method of cryptographic computation to generate output data from input data and from a secret key includes a derived key scheduling step to provide a derived key from the secret key according to a known key scheduling operation. The method also includes a masking step, performed before the derived key scheduling step, to mask the secret key so that the derived scheduled key is different at each implementation of the method. The present method and component can be used in transfer type applications, such as bank type applications.
The encryption device includes a random number generator for generating a random number; and a first selector for selecting one of q fixed values in response to the random number, a second selector for selecting one set of q sets of fixed S-box tables in response to the random number. An XOR XORs an input with an XOR of a key with the fixed value. A nonlinear transform transforms an input nonlinearly in accordance with the selected set of fixed S-box tables. Another encryption device includes a plurality of encrypting units coupled in parallel, and a selector for selecting one of the plurality of encrypting units in response to the random number. The masking with the fixed values improves the processing speed and reduces the required RAM area.
