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Symmetric key encryption system with synchronously updating expanded key

  • US 8,041,032 B2
  • Filed: 08/19/2005
  • Issued: 10/18/2011
  • Est. Priority Date: 08/19/2005
  • Status: Active Grant
First Claim
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1. A method comprising:

  • using at least one processor able to execute instructions to;

    receive a cipher key;

    expand the cipher key into a plurality of round keys;

    create a pre-cipher, based at least in part upon the cipher key and the plurality of round keys;

    receive a message comprising a plurality of ciphertext blocks;

    use the pre-cipher to decrypt the plurality of ciphertext blocks, yielding a plurality of plaintext blocks;

    during decryption of the message;

    inspect a designated portion of the last plaintext block of the plurality of plaintext blocks to determine whether a pre-cipher reconfiguration parameter is non-zero; and

    when the pre-cipher reconfiguration parameter is non-zero;

    extract the pre-cipher reconfiguration parameter from the plaintext block; and

    alter the pre-cipher based upon the reconfiguration parameter, to provide an altered pre-cipher.

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