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Construction symmetric ciphers using the cast design procedure

  • US 5,825,886 A
  • Filed: 12/05/1996
  • Issued: 10/20/1998
  • Est. Priority Date: 12/08/1995
  • Status: Expired due to Term
First Claim
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1. In a data encryption method of cryptographically transforming plaintext into ciphertext in data blocks of a predetermined bitlength comprising a plurality of consecutive transformation rounds of half of each data block, each consecutive transformation round comprising steps of:

  • combining the half data block with a first masking key of predetermined length using a first binary operation to generate a first modified half data block;

    combining the first modified half data block with a second masking key of predetermined length using a second and different binary operation to generate a second modified half data block;

    processing the second modified half data block by a plurality of (m×

    n) mutually different substitution boxes to generate a third modified half data block, m and n being positive integers; and

    XORing the third modified half data block with the remaining half of the data block to generate a transformed half data block of a transformation round.

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