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Secure electronic messaging system requiring key retrieval for deriving decryption keys

  • US 20030147536A1
  • Filed: 02/05/2002
  • Published: 08/07/2003
  • Est. Priority Date: 02/05/2002
  • Status: Active Grant
First Claim
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1. A method for secure communication of a message M between a sender and a recipient, with the assistance of a key server, the method comprising the steps of:

  • the sender encrypting the message M with a symmetric key Ks to form an encrypted message;

    the sender encrypting first information derived from the symmetric key Ks, using a public encryption key Ke of the recipient;

    the key server storing decryption key information needed by the recipient to form a decryption key suitable for decrypting the encrypted message;

    the sender receiving key retrieval information Kr which indexes the decryption key information;

    the sender sending to the recipient, at least the encrypted message and the key retrieval information Kr;

    the recipient sending the key retrieval information Kr to the key server and receiving the decryption key information in response thereto;

    the recipient forming the symmetric key Ks from at least the decryption key information and a private decryption key Kd of the recipient; and

    the recipient decrypting the encrypted message with the symmetric key Ks;

    without the message or the encrypted message being sent to the key server.

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