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Cryptographic system with masking

  • US 5,768,390 A
  • Filed: 07/17/1997
  • Issued: 06/16/1998
  • Est. Priority Date: 10/25/1995
  • Status: Expired due to Term
First Claim
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1. A computer-implemented method of cryptographically transforming a sequence of input blocks of data into a corresponding sequence of output blocks of data, said sequence of input blocks comprising a first input block and one or more subsequent input blocks, each of said one or more subsequent input blocks having a previous input block, said method comprising the steps of:

  • enciphering each input block using a first key to generate a first encryption product;

    combining each first encryption product by modular addition with a first secret masking value to generate a masked first encryption product, said first secret masking value being generated independently of said input blocks and being different for each subsequent input block;

    enciphering each masked first encryption product using a second key to generate a second encryption product;

    combining each second encryption product by modular addition with a second secret masking value to generate a masked second encryption product, said second secret masking value being generated independently of said input blocks and being different for each subsequent input block; and

    enciphering each masked second encryption product using a third key to generate an output block corresponding to said input block.

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