Patent ID: 7318161

Claim:
A file retrieval method of retrieving records that satisfy retrieval conditions from an at least partly encrypted file, said file retrieval method comprising the steps of: A) in a file comprising an assemblage of records, each record having a record number and plural encrypted and unencrypted fields which make up database information fields, and at least one field among said plurality of fields being an encrypted retrieval key, decrypting the encrypted retrieval keys in each record, attaching identifiers to the decrypted retrieval keys to indicate to which records the decrypted retrieval keys belong, and expanding said decrypted keys and said identifiers in a main memory, remaining fields of each record not being retrieved from the file and expanded into the main memory; and B) after making a test of each decrypted retrieval keys for satisfying retrieval conditions, retrieving, from the file, the remaining fields of records with decrypted retrieval keys that satisfy the retrieval conditions.