Method for masking secret multiplicands
AssigneeEricsson Inc.
InventorsPaul W. Dent, Michael Kornby
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Abstract
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.
Claims20
A method of thwarting detection of a secret binary number in a cryptographic computational device by analysis of externally observable parameters, comprising:
- conditionally performing a plurality of calculations in response to the bit values of said secret number;
- multiplicatively accumulating the results of said plurality of calculations in a subtotal;
- and
- performing dummy calculations in response to selected bit positions of said secret number that indicate calculations should not be performed, and not multiplicatively accumulating the results of the dummy calculations in said subtotal, said selected bit positions randomly distributed over a binary indicator equal in length to said secret number;
- whereby said dummy calculations alter at least one externally observable parameter.
A detection-proof computational device comprising:
- an input/output interface;
- a memory storing a secret binary number;
- and
- a processor operatively connected to said input/output interface and to said memory and programmed for cryptographic computation using said secret binary number while thwarting detection of said secret binary number by analysis of externally observable parameters, the cryptographic computation comprising:
- conditionally performing a plurality of calculations in response to the bit values of said secret number;
- multiplicatively accumulating the results of said plurality of calculations in a subtotal;
- and
- performing dummy calculations in response to selected bit positions of said secret number that indicate calculations should not be performed, and not multiplicatively accumulating the results of the dummy calculations in said subtotal, said selected bit positions randomly distributed over a binary indicator equal in length to said secret number;
- whereby said dummy calculations alter at least one externally observable parameter.
A mobile terminal used in a mobile communications system comprising:
- a transmitter and a receiver for communicating in the mobile communications system;
- a controller controlling operation of the transmitter and the receiver;
- and
- a secure device removably, operatively connectable to the controller and comprising:
- an input/output interface;
- a memory storing a secret binary number;
- and
- a processor operatively connected to said input/output interface and to said memory and programmed for cryptographic computation using said secret binary number while thwarting detection of said secret binary number by analysis of externally observable parameters, the cryptographic computation comprising:
- conditionally performing a plurality of calculations in response to the bit values of said secret number;
- multiplicatively accumulating the results of said plurality of calculations in a subtotal;
- and
- performing dummy calculations in response to selected bit positions of said secret number that indicate calculations should not be performed, and not multiplicatively accumulating the results of the dummy calculations in said subtotal, said selected bit positions randomly distributed over a binary indicator equal in length to said secret number;
- whereby said dummy calculations alter at least one externally observable parameter.
Dependencies are inferred from the claim text.