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Payment smart cards with hierarchical session key derivation providing security against differential power analysis and other attacks

  • US 9,940,772 B2
  • Filed: 10/24/2007
  • Issued: 04/10/2018
  • Est. Priority Date: 07/02/1998
  • Status: Expired due to Fees
First Claim
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1. A cryptographic device comprising:

  • (a) at least one memory containing a value of a secret parameter; and

    (b) a processor configured to perform a plurality of cryptographic transactions,each said transaction involving a cryptographically processed datum, where;

    (i) each of said cryptographic transactions is secured using a secret parameter;

    (ii) said processor configured to reduce the usefulness of information gathered through external monitoring of said cryptographic device related to said secret parameter by performing a plurality of cryptographic update operations to derive an updated value of said secret parameter at a different level within a hierarchy of secret parameters, wherein deriving an updated value of said secret parameter comprises applying at least one invertible function to the value of said secret parameter before said plurality of cryptographic operations; and

    (iii) said processor configured to store the updated value of said secret parameter in said at least one memory for use in at least one subsequent transaction; and

    (c) an interface configured to output said datum to a cryptographic processing device.

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