https://shkspr.mobi/blog/2025/03/towards-extracting-content-from-an-lcp-protected-epub/

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2025-03-16

Extracting content from an LCP "protected" ePub

@edent[a]debugging drm ebooks epub * 10 comments * 1,800 words *
read ~6,253 times.

---------------------------------------------------------------------
 

As Cory Doctorow once said "Any time that someone puts a lock on
something that belongs to you but won't give you the key, that lock's
not there for you."

But here's the thing with the LCP DRM scheme; they do give you the
key! As I've written about previously, LCP mostly relies on the user
entering their password (the key) when they want to read the book.
Oh, there's some deep cryptographic magic in the background but,
ultimately, the key is sat on your computer waiting to be found. Of
course, cryptography is Very Hard(tm) which make retrieving the key
almost impossible - so perhaps we can use a different technique to
extract the unencrypted content?

One popular LCP app is Thorium. It is an Electron Web App. That means
it is a bundled browser running JavaScript. That also means it can
trivially be debugged. The code is running on your own computer, it
doesn't touch anyone else's machine. There's no reverse engineering.
No cracking of cryptographic secrets. No circumvention of any
technical control. It doesn't reveal any illegal numbers. It doesn't
jailbreak anything. We simply ask the reader to give us the content
we've paid for - and it agrees.

Here Be Dragons

This is a manual, error-prone, and tiresome process. This cannot be
used to automatically remove DRM. I've only tested this on Linux. It
must only be used on books that you have legally acquired. I am using
it for research and private study.

This uses Thorium 3.1.0 AppImage.

First, extract the application:

BASH BASH./Thorium-3.1.0.AppImage --appimage-extract

That creates a directory called squashfs-root which contains all the
app's code.

The Thorium app can be run with remote debugging enabled by using:

BASH BASH./squashfs-root/thorium --remote-debugging-port=9223 --remote-allow-origins=*

Within the Thorium app, open up the book you want to read.

Open up Chrome and go to http://localhost:9223/ - you will see a list
of Thorium windows. Click on the link which relates to your book.

In the Thorium book window, navigate through your book. In the debug
window, you should see the text and images pop up.

Chrome debug screen.

In the debug window's "Content" tab, you'll be able to see the images
and HTML that the eBook contains.

Images

The images are the full resolution files decrypted from your ePub.
They can be right-clicked and saved from the developer tools.

Files

An ePub file is just a zipped collection of files. Get a copy of your
ePub and rename it to whatever.zip then extract it. You will now be
able to see the names of all the files - images, css, fonts, text,
etc - but their contents will be encrypted, so you can't open them.

You can, however, give their filenames to the Electron app and it
will read them for you.

Images

To get a Base64 encoded version of an image, run this command in the
debug console:

JavaScript JavaScriptfetch("httpsr2://...--/xthoriumhttps/ip0.0.0.0/p/OEBPS/image/whatever.jpg") .then(response => response.arrayBuffer())

  .then(buffer => {

    let base64 = btoa(

      new Uint8Array(buffer).reduce((data, byte) => data + String.fromCharCode(byte), '')

    );

    console.log(`data:image/jpeg;base64,${base64}`);

  });

Thorium uses the httpsr2 URl scheme - you can find the exact URl by
looking at the content tab.

CSS

The CSS can be read directly and printed to the console:

JavaScript JavaScriptfetch("httpsr2://....--/xthoriumhttps/ip0.0.0.0/p/OEBPS/css/styles.css").then(response => response.text())

  .then(cssText => console.log(cssText));

However, it is much larger than the original CSS - presumably because
Thorium has injected its own directives in there.

Metadata

Metadata like the NCX and the OPF can also be decrypted without
problem:

JavaScript JavaScriptfetch("httpsr2://....--/xthoriumhttps/ip0.0.0.0/p/OEBPS/content.opf").then(response => response.text())

  .then(metadata => console.log(metadata));

They have roughly the same filesize as their encrypted counterparts -
so I don't think anything is missing from them.

Fonts

If a font has been used in the document, it should be available. It
can be grabbed as Base64 encoded text to the console using:

JavaScript JavaScriptfetch("httpsr2://....--/xthoriumhttps/ip0.0.0.0/p/OEBPS/font/Whatever.ttf") .then(response => response.arrayBuffer())

  .then(buffer => {

    let base64 = btoa(

      new Uint8Array(buffer).reduce((data, byte) => data + String.fromCharCode(byte), '')

    );

    console.log(`${base64}`);

  });

From there it can be copied into a new file and then decoded.

Text

The HTML of the book is also visible on the Content tab. It is not
the original content from the ePub. It has a bunch of CSS and JS
added to it. But, once you get to the body, you'll see something
like:

HTML HTML<body>

    <section epub:type="chapter" role="doc-chapter">

        <h2 id="_idParaDest-7" class="ct"><a id="_idTextAnchor007"></a><span id="page75" role="doc-pagebreak" aria-label="75" epub:type="pagebreak"></span>Book Title</h2>

        <div class="_idGenObjectLayout-1">

            <figure class="Full-Cover-White">

                <img class="_idGenObjectAttribute-1" src="image/cover.jpg" alt="" />

            </figure>

        </div>

        <div id="page76" role="doc-pagebreak" aria-label="76" epub:type="pagebreak" />

        <section class="summary"><h3 class="summary"><span class="border">SUMMARY</span></h3>

        <p class="BT-Sans-left-align---p1">Lorem ipsum etc.</p>

    </section>

Which looks like plain old ePub to me. You can use the fetch command
as above, but you'll still get the verbose version of the xHTML.

Putting it all together

If you've unzipped the original ePub, you'll see the internal
directory structure. It should look something like this:

+-- META-INF

|   +-- container.xml

+-- mimetype

+-- OEBPS

    +-- content.opf

    +-- images

    |   +-- cover.jpg

    |   +-- image1.jpg

    |   +-- image2.png

    +-- styles

    |   +-- styles.css

    +-- content

    |   +-- 001-cover.xhtml

    |   +-- 002-about.xhtml

    |   +-- 003-title.xhtml

    |   +-- 004-chapter_01.xhtml

    |   +-- 005-chapter_02.xhtml

    |   +-- 006-chapter_03.xhtml

    +-- toc.ncx

Add the extracted files into that exact structure. Then zip them.
Rename the .zip to .epub. That's it. You now have a DRM-free copy of
the book that you purchased.

BONUS! PDF Extraction

LCP 2.0 PDFs are also extractable. Again, you'll need to open your
purchased PDF in Thorium with debug mode active. In the debugger, you
should be able to find the URl for the decrypted PDF.

It can be fetched with:

JavaScript JavaScriptfetch("thoriumhttps://0.0.0.0/pub/..../publication.pdf") .then(response => response.arrayBuffer())

  .then(buffer => {

    let base64 = btoa(

      new Uint8Array(buffer).reduce((data, byte) => data + String.fromCharCode(byte), '')

    );

    console.log(`${base64}`);

  });

Copy the output and Base64 decode it. You'll have an unencumbered
PDF.

Next Steps

That's probably about as far as I am competent to take this.

But, for now, a solution exists. If I ever buy an ePub with LCP
Profile 2.0 encryption, I'll be able to manually extract what I need
from it - without reverse engineering the encryption scheme.

Ethics

Before I published this blog post, I publicised my findings on
Mastodon. Shortly afterwards, I received a LinkedIn message from
someone senior in the Readium consortium - the body which has created
the LCP DRM.

They said:

    Hi Terence, You've found a way to hack LCP using Thorium. Bravo!
    We certainly didn't sufficiently protect the system, we are
    already working on that. From your Mastodon messages, you want to
    post your solution on your blog. This is what triggers my
    message. From a manual solution, others will create a one-click
    solution. As you say, LCP is a "reasonably inoffensive"
    protection. We managed to convince publishers (even big US
    publishers) to adopt a solution that is flexible for readers and
    appreciated by public libraries and booksellers. Our gains are
    re-injected in open-source software and open standards (work on
    EPUB and Web Publications). If the DRM does not succeed, harder
    DRMs (for users) will be tested. I let you think about that
    aspect

I did indeed think about that aspect. A day later I replied, saying:

    Thank you for your message. Because Readium doesn't freely
    licence its DRM, it has an adverse effect on me and other readers
    like me.
      + My eReader hardware is out of support from the manufacturer -
        it will never receive an update for LCP support.
      + My reading software (KOReader) have publicly stated that they
        cannot afford the fees you charge and will not be certified
        by you.
      + Kobo hardware cannot read LCP protected books.
      + There is no guarantee that LCP compatible software will be
        released for future platforms.
    In short, I want to read my books on my choice of hardware and
    software; not yours. I believe that everyone deserves the right
    to read on their platform of choice without having to seek
    permission from a 3rd party. The technique I have discovered is
    basic. It is an unsophisticated use of your app's built-in
    debugging functionality. I have not reverse engineered your code,
    nor have I decrypted your secret keys. I will not be publishing
    any of your intellectual property. In the spirit of openness, I
    intend to publish my research this week, alongside our
    correspondence.

Their reply, shortly before publication, contained what I consider to
be a crude attempt at emotional manipulation.

    Obviously, we are on different sides of the channel on the
    subject of DRMs. I agree there should be many more LCP-compliant
    apps and devices; one hundred is insufficient. KOReader never
    contacted us: I don't think they know how low the certification
    fee would be (pricing is visible on the EDRLab website).
    FBReader, another open-source reading app, supports LCP on its
    downloadable version. Kobo support is coming. Also, too few
    people know that certification is free for specialised devices
    (e.g. braille and audio devices from Hims or Humanware). We were
    planning to now focus on new accessibility features on our
    open-source Thorium Reader, better access to annotations for
    blind users and an advanced reading mode for dyslexic people. Too
    bad; disturbances around LCP will force us to focus on a new
    round of security measures, ensuring the technology stays useful
    for ebook lending (stop reading after some time) and as a
    protection against oversharing. You can, for sure, publish
    information relative to your discoveries to the extent UK laws
    allow. After study, we'll do our best to make the technology more
    robust. If your discourse represents a circumvention of this
    technical protection measure, we'll command a take-down as a
    standard procedure.

A bit of a self-own to admit that they failed to properly prioritise
accessibility!

Rather than rebut all their points, I decided to keep my reply
succinct.

    As you have raised the possibility of legal action, I think it is
    best that we terminate this conversation.

I sincerely believe that this post is a legitimate attempt to educate
people about the deficiencies in Readium's DRM scheme. Both readers
and publishers need to be aware that their Thorium app easily allows
access to unprotected content.

I will, of course, publish any further correspondence related to this
issue.

---------------------------------------------------------------------

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10 thoughts on "Extracting content from an LCP "protected" ePub"

 1. 2025-03-16 16:15
    [b1fdbd08]

    Lord Hanuman Parwat says:

    Thanks for the detailed write. All DRMs are technically bad, this
    is not news. It is worth knowing that using Thorium on Linux
    makes it even easier to copy content: Ctrl+A to copy all the text
    of a chapter, and middle click to copy. copy/paste is disallowed
    on windows and macos, but not easy to do on linux.
    Reply
 2. 2025-03-17 07:26
    []

    [www] mobileread.com said on www.mobileread.com:

    LCP DRM - Extracting Files General Discussions
    Reply | Reply to original comment on www.mobileread.com
 3. 2025-03-17 12:49
    [bafkreig]

    [bsky] Oliver Turner said on bsky.app:

    Thank you for standing up for user rights and accessibility, and
    bravo for not taking any of their manipulative nonsense   
    Reply | Reply to original comment on bsky.app
 4. 2025-03-17 14:56
    []

    [news] news.ycombinator.com said on news.ycombinator.com:

    Extracting content from an LCP "protected" ePub | Hacker News
    Reply | Reply to original comment on news.ycombinator.com
 5. 2025-03-17 15:11
    [6470ed62]

    [danq] Dan Q says:

    You'd think that companies would have learned by now not to
    lampshade things like this. When I saw you write about it on
    Mastodon, I thought, "huh, okay, that's interesting." But now
    you've published it on your blog, alongside their comment that
    they're seeking to be able to make a takedown notice, I'm instead
    thinking "huh, better archive a copy of this so I can upload the
    findings to as many places as possible in the event that it
    disappears from the Internet." (I don't expect any response from
    you to this comment, and that's fine.)
    Reply
 6. 2025-03-17 15:15
    [cb81346e]

    [universeod] WokStation said on universeodon.com:

    @Edent had they not whined so hard, I'd not have heard of this,
    and I certainly wouldn't, therefore, be sharing it either!

    Reply | Reply to original comment on universeodon.com
 7. 2025-03-17 15:27
    [20a1b51f]

    [digipres] raffaele said on digipres.club:

    @Edent Readium's position on communicating these flaws is not
    brilliant, even worse is the threat to avoid publication. But
    consider that LCP is not just a DRM for vendors, it is widely
    used for digital lending in public libraries, even the Internet
    Archive uses it. If publishers lose confidence, that means they
    might decide not to lend digital content to libraries (where
    people read freely) Your research is good and should be used to
    collectively improve the ecosystem https://github.com/edrlab/
    thorium-reader/discussions

    edrlab thorium-reader * Discussions
    Reply | Reply to original comment on digipres.club
 8. 2025-03-17 20:14
    [28d7ff8a]

    [shark] Taylor said on shark.axfive.net:

    @Edent@mastodon.social Good work! Shame on Readium for the
    aggressive response. Kind of bizarre, even if they took issue
    with it, the correct answer would have been to either ignore your
    blog, strengthen their encryption to block what you're doing, or
    to just take the legal action. This is just terrible PR for no
    gain.

    Reply | Reply to original comment on shark.axfive.net
 9. 2025-03-17 20:43
    [bafkreif]

    [bsky] Andy Loughran said on bsky.app:

    Thank you for your time and the write up.  
    Reply | Reply to original comment on bsky.app
10. [svg]

    More comments on Mastodon.

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 1. 2025-03-16 15:26

    [geek] Cong LCP"Shou Bao Hu "De ePubZhong Ti Qu Nei Rong  - Pian Zhi De Ma Nong :

    [...] Xiang Qing Can Kao  [...]

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