Cryptographic authentication of transmitted messages using pseudorandom numbers

  • US RE36,752 E
  • Filed: 12/23/1996
  • Issued: 06/27/2000
  • Est. Priority Date: 06/30/1993
  • Status: Expired due to Term
First Claim
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1. A method of cryptographically authenticating a transmission from a transmitting unit at a receiving module, comprising:

  • providing a secret initial value in said transmitter andproviding said secret initial value in said receiver;

    in said transmitting unit;

    generating a random number;

    concatenating said random number with a key word derived from said secret initial value to provide a combined word;

    performing an encryption operation on said combined word to provide an encrypted number; and

    transmitting a command word derived at least in part from said encrypted number and indicative of a command;

    comprising in said receiving module;

    receiving said command word;

    recovering said encrypted number from said received command word;

    performing a decryption operation on said recovered encrypted number to recover said combined word;

    comparing a second word derived from said secret initial value with the key word portion of said recovered combined word;

    storing the random number portion of said recovered combined word for future use in subsequent authentication operations;

    comparing the random number portion of said recovered combined word with a previously stored random number portion; and

    performing the command indicated by said command word only if said second .[.secret initial value.]. .Iadd.word .Iaddend.is identical to the .[.initial value.]. .Iadd.key word .Iaddend.portion of said recovered combined word and said random number portion of said recovered combined word is different from said previously stored random number portion.

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