| 摘要 |
A database ( 104 ) maintains one or more groups ( 106 ) of digital objects ( 202 ). A user ( 102 ) wishes to retrieve one or more digital objects ( 202 ) from the database ( 104 ), without the database ( 104 ) being able to determine which particular digital objects ( 202 ) have been retrieved. In addition, the database ( 104 ) should not allow the user ( 102 ) to retrieve any digital objects ( 202 ) to which the user ( 102 ) has not been granted access. The user ( 102 ) requests the groups ( 106 ) containing the digital objects ( 202 ) the user ( 102 ) wishes to download, but does not identify the digital objects ( 202 ) within each group ( 106 ) that the user ( 102 ) is interested in. Using a symmetric key cryptosystem, the database ( 104 ) generates a key ( 204 ) for and encrypts each digital object ( 202 ) in the requested group ( 106 ) into ciphertext ( 206 ), and additionally encrypts each key ( 204 ). The database ( 104 ) transmits the ciphertexts ( 206 ) and encrypted keys ( 208 ) to the user ( 102 ). The user ( 102 ) identifies the keys ( 208 ) associated with the digital objects ( 202 ) of interest, and further encrypts the keys ( 208 ), returning the changed keys ( 506 ) to the A database ( 104 ). The database ( 104 ) reverses its encryption of the keys ( 506 ), and transmits the partially decrypted keys ( 510 ) back to the user ( 102 ). The user ( 102 ) then applies the user's ( 102 ) own decryption algorithm to the keys ( 510 ), and then uses the decrypted keys ( 204 ) to decrypt the digital objects ( 202 ) of interest. |
