EPUB Unit File Compression and Encryption Strategy

The patent segments the EPUB file processing into two distinct paths: encrypted unit files are compressed individually before encryption, while non-encrypted unit files are compressed separately. This segmentation allows compression to occur on plaintext data (maintaining efficiency) while still achieving security through subsequent encryption, resolving the contradiction between security and compression efficiency.

The patent applies preliminary compression to unit files before encryption. By compressing the data in its plaintext state first, the system achieves optimal compression ratios. The encrypted data is then packaged without further compression, maintaining the compression efficiency that would be lost if encryption preceded compression.

The patent divides the compressed file structure into segments: encrypted unit files are compressed and packaged separately from non-encrypted unit files. The packaging process creates a structured container that organizes these segments while preserving the ability to apply different compression and encryption treatments to each segment, thus maintaining compression efficiency while managing file structure complexity.

The patent applies different quality treatments to different parts of the EPUB file system. Encrypted unit files receive compression followed by encryption, while non-encrypted unit files receive only compression. This local differentiation allows each file type to be treated optimally, maintaining overall compression efficiency while achieving security where needed.