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Secret key transfer method which is highly secure and can restrict the damage caused when the secret key is leaked or decoded

  • US 6,009,174 A
  • Filed: 10/27/1997
  • Issued: 12/28/1999
  • Est. Priority Date: 10/31/1996
  • Status: Expired due to Term
First Claim
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1. A secret key transfer technique, used in an encrypted communication system composed of a transmission apparatus and a reception apparatus which perform encrypted communication using one secret key selected out of a plurality of secret keys, whereby the transmission apparatus informs the reception apparatus of the selected secret key,the transmission apparatus comprising:

  • first secret key storing means for storing the plurality of secret keys;

    secret key selecting means for selecting one secret key out of the plurality of secret keys stored in the first secret key storing means;

    message generating means for generating a message;

    first encrypting means for encrypting the message according to a first encryption algorithm using the secret key selected by the secret key selecting means as an encryption key to produce a first cryptogram;

    second encrypting means for encrypting the message according to a second encryption algorithm using the message as an encryption key to produce a second cryptogram; and

    transferring means for transferring the first cryptogram and the second cryptogram to the reception apparatus,and the reception apparatus comprising;

    second secret key storing means for storing the plurality of secret keys;

    reception means for receiving the first cryptogram and the second cryptogram transferred from the transmission apparatus;

    first decrypting means for decrypting the received first cryptogram according to a first decryption algorithm using one secret key selected from the plurality of secret keys as a decryption key to produce a first set of decrypted data, wherein the first decryption algorithm is an inverse transformation of the first encryption algorithm;

    second decrypting means for decrypting the received second cryptogram according to a second decryption algorithm using the first set of decrypted data as a decryption key to produce a second set of decrypted data, wherein the second decryption algorithm is an inverse transformation of the second encryption algorithm;

    judging means for judging whether the first set of decrypted data matches the second set of decrypted data and, when the sets of decrypted data match, for authorizing that the secret key used by the first decryption means is the secret key selected by the transmission apparatus; and

    repetition control means for having a decryption by the first decrypting means, a decryption by the second decrypting means, and a judgement and an authorization by the judging means repeated for each of the plurality of secret keys in the second secret key storage means in order.

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