Encryption scheme for limiting the maximum number of accesses to a digital file of predetermined content

摘要

A method and system for providing access to a data file enables predetermination of the number of times the file is accessible. The data file is encrypted with a master key, and one or more dual-encrypted blocks are generated based on a set of secondary keys. The dual-encrypted blocks are contained within the encrypted data file. The method further provides for providing the encrypted data file and an attachment file to an authorized user, where the attachment file enables a device to access the data file content once for each secondary key. The file is accessed by decrypting single-encrypted blocks of the data file with a master key. Dual-encrypted blocks of the data file are decrypted with the master key and a secondary key. The decryption steps are repeated for a set of secondary keys such that the device is able to access the data file content once for each secondary key in the set.