Patent ID: 8312295

Claim:
An access key generating apparatus comprising: a bit field converting unit which converts a partial bit field, as a portion of a bit field indicating a device identifier of peripheral devices, into a reduced bit field having a bit width shorter than a bit width of the partial bit field; an access key retaining unit which retains a plurality of access keys to control access to a memory from the peripheral devices in association with each of the peripheral devices; an indexing unit which indexes the access keys from the access key retaining unit using an index address including the reduced bit field if the conversion of the partial bit field into the reduced bit field is successful, and indexes the access keys from the access key retaining unit using an index address including the partial bit field if the conversion of the partial bit field into the reduced bit field is unsuccessful; wherein the device identifier includes the bus number and a device number, and wherein the indexing unit indexes the access keys from the access key retaining unit using an index address including the reduced bus number and the device number if the conversion of the bus number into the reduced bus number is successful, and indexes the access keys from the access key retaining unit using an index address including the bus number if the conversion of the bus number into the reduced bus number is unsuccessful.