How to make an EPUB file read-only/non-modifiable?

[Abdo]

Hello everyone,

I'm looking for a way to protect my EPUB files from being modified. I want to create a read-only version that prevents editing while still being readable in standard ebook readers.

My specific constraints:

• The EPUB contains audio elements (so PDF conversion isn't suitable)
  
• I primarily use Calibre for reading and Sigil for editing
  
• I prefer solutions using these tools rather than additional software
  
• I don't want to use DRM protection

What I've tried:

• Setting file permissions to "read-only" in the OS
  
• Configuring Calibre settings to prevent writing annotations back to the file

Questions:

• Are there specific Calibre settings to make EPUBs open in read-only mode?
  
• Can Sigil be used to create a protected version?
  
• Are there EPUB-specific features (like FXL - Fixed Layout) that make modification more difficult?
  
• What are the best practices for EPUB protection without DRM?

Any suggestions or step-by-step guidance would be greatly appreciated!

[Quoth]

Distribute on CD

FXL is a horrid alternate to PDF.

What I think you want to do is nearly impossible and why anyway?

A read-only OS file can be edited as soon as a copy is made.

What are you wanting to achieve?

[Karellen]

I guess that is why DRM exists- Authors want to protect their works just like you are trying to do.

If there was another way to do it without using DRM, I am pretty sure we would have seen it by now, and there would be multiple threads on the forum discussing it.

And like Quoth stated, no matter what method you use, there is always a way around it.

[Quoth]

And DRM is an evil nonsense.

[JSWolf]

@Abdo, what you want to do is not possible.

[Doitsu]

Originally Posted by Abdo

• The EPUB contains audio elements (so PDF conversion isn't suitable)

You can embed or attach audio files to PDF documents.

Originally Posted by Abdo

• Are there EPUB-specific features (like FXL - Fixed Layout) that make modification more difficult?

It's slightly off-spec, but you could theoretically obfuscate the first 1040 bytes in all files, except for the .opf file. But that obfuscation could be easily reverted. It'll also trigger the following EPUBCheck error message for all non-font files:

ERROR(PKG-026): obfuscation_test.epub/META-INF/encryption.xml(24,58): Obfuscated resource must be a Font Core Media Type (was declared as "XXX/XXX" in "OEBPS/content.opf").

My test file displays fine in Thorium, ADE 4.5 and Calibre E-Book Viewer, but it can no longer be edited with Sigil, because all .xhtml, .css, .png and .ttf files have been obfuscated.