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System and method for protecting data files by periodically refreshing a decryption key

  • US 6,937,726 B1
  • Filed: 12/21/1999
  • Issued: 08/30/2005
  • Est. Priority Date: 04/06/1999
  • Status: Expired due to Fees
First Claim
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1. A method for protecting a data file on a computer system, comprising the steps of:

  • providing a grantee'"'"'s encryption key, a grantee'"'"'s decryption key, a grantor'"'"'s encryption key, and a grantor'"'"'s decryption key;

    using asymmetric encryption, encrypting the data file using the grantor'"'"'s encryption key to create an encrypted data file;

    generating a transformation key from the grantor'"'"'s decryption key, the grantee'"'"'s encryption key and other data which is data file independent;

    transforming the encrypted data file with the transformation of the encrypted data file does not reveal the data file during the process of transforming;

    providing the transformed encrypted data file to the grantee; and

    decrypting the transformed encrypted file by the grantee with the grantee'"'"'s decryption key;

    wherein the transformation key does not allow the grantee to determine the grantor'"'"'s decryption key.

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