how to de-obfuscate fonts in an epub

trysem · 12-01-2022, 02:05 PM

I am new to this field, I have an ebook being purchased, and I want to read it in another reader than the native, but it opens obfuscated.
what do I need to do de-obfuscate it?
what do I need to have, to deobfuscate? any ID (red somewhere)

KevinH · 12-01-2022, 03:17 PM

All valid epub readers successfully handle the de-obfuscation of fonts properly and internally. Trying to copy those fonts out of the epub they were intended for to use in some other epub is the only way you can cause an issue with auto obfuscation and de-obfuscation. Is that what you are trying to do? If so, that is exactly what font obfuscation was meant to prevent.

Quoth · 12-01-2022, 04:52 PM

Either leave it alone or replace the fonts entirely with your own suitable face/style "free fonts" using Calibre Editor Font Manager.

DNSB · 12-01-2022, 07:03 PM

Quote:

Originally Posted by KevinH

All valid epub readers successfully handle the de-obfuscation of fonts properly and internally. Trying to copy those fonts out of the epub they were intended for to use in some other epub is the only way you can cause an issue with auto obfuscation and de-obfuscation. Is that what you are trying to do? If so, that is exactly what font obfuscation was meant to prevent.

Or if it is being converted to a different format, the identifier used for the de-obfuscation is not being preserved.

KevinH · 12-01-2022, 07:35 PM

Agreed. Or someone discarded the encrypt.xml from the META-INF folder by mistake as it is needed to tell the reader which fonts are obfuscated. Or manually edited the opf and erased the key identifiers.

trysem · 12-01-2022, 10:46 PM

Quote:

Originally Posted by KevinH

All valid epub readers successfully handle the de-obfuscation of fonts properly and internally. Trying to copy those fonts out of the epub they were intended for to use in some other epub is the only way you can cause an issue with auto obfuscation and de-obfuscation. Is that what you are trying to do? If so, that is exactly what font obfuscation was meant to prevent.

Am not about fonts, my concern is, i wanted to read it in a better reader in a better environment..
As am not tech savvy, could you pls tell me how to get rid obfuscation..
Glad you there to reply, just surfing this forum before, i tried sigil also, but i dont know how to do it..
i have also seen something like "dc:classifier" in content.opf, does this id help in anything?
could you pls guide me to deobfuscate or to change font with proper editing needed files.

trysem · 12-01-2022, 10:55 PM

Quote:

Originally Posted by DNSB

Or if it is being converted to a different format, the identifier used for the de-obfuscation is not being preserved.

Whats the big deal about identifiers? Do i need to deobfuscate? It uses idpf encryption or something (content.opf ).
is that a key to de-obfuscate?

KevinH · 12-02-2022, 10:13 AM

Changing to a different epub ereader should never require manually deobfuscating anything.

The list of obfuscated fonts and obfuscation method is provided by the encrypt.xml file found in the epub's META-INF folder. The data used to obfuscate and deobfuscate depends on obfuscation method and is tied to a specific dc:identifiers in the opf metadata this is sometimes the bookid and another uuid based dc:identifiers. The actually obfuscation algorithm involves a fixed number of bytes (again differs by algorithm) at the top of the font file being xored with data from the opf identifier in a very specific manner. The exact algorithm has been published in the epub spec. But this is not something you can easily manually undo.

So as explained earlier, unzip your epub, throw away the broken font files, replace them with known good matching font files (rename exact file if needed), then remove the entire encrypt.xml from the META-INF folder as keeping it will mistakenly cause the reader to obfuscate the font files on load instead of deobfuscating them.

Properly rezip up the epub.

trysem · 12-02-2022, 10:50 AM

The list of obfuscated fonts and obfuscation method is provided by the encrypt.xml file found in the epub's META-INF folder. The data used to obfuscate and deobfuscate depends on obfuscation method and is tied to a specific dc:identifiers in the opf metadata this is sometimes the bookid and another uuid based dc:identifiers. The actually obfuscation algorithm involves a fixed number of bytes (again differs by algorithm) at the top of the font file being xored with data from the opf identifier in a very specific manner. The exact algorithm has been published in the epub spec. But this is not something you can easily manually undo.

So as explained earlier, unzip your epub, throw away the broken font files, replace them with known good matching font files (rename exact file if needed), then remove the entire encrypt.xml from the META-INF folder as keeping it will mistakenly cause the reader to obfuscate the font files on load instead of deobfuscating them.

Properly rezip up the epub.[/QUOTE]

My case Is, i bought 3 books from a vendor which happens to be one of main publisher of our language "malayalam".
As we know, it can only be opened with desired android app. The app is highly ancient and a total mess.

So first i thought it might some custom DRM or something (actually am not sure). But later on , after surging somewhere like mobileread..etc i found obfuscation.
I have seen there, the encrypt.xml, and idpf encryption in it, so i thought it might be obfuscation.

Any other reader is throwing error, i cant read..
Please help me if possible......

KevinH · 12-02-2022, 11:32 AM

If you can unzip the epub and open one of the xhtml/html files in a text editor and it can be read by you, then your epub has no drm and you should do what I said above.

If you can not read the text of the xhtml file in a text efitor, then it has drm and we can not help you, as the problem has nothing to do with font obfuscation.

Quoth · 12-02-2022, 01:52 PM

Probably there is also DRM if it only works in the seller's app.

trysem · 12-02-2022, 03:42 PM

I cant read,
Then probably it will be DRM i think..
I think its something custom DRM, any scope in de -DRM? Using any of the tools?

KevinH · 12-02-2022, 05:34 PM

No idea. Check with the author of the deDRM plugin, not here on mobileread.

jhowell · 12-02-2022, 06:39 PM

Quote:

Originally Posted by trysem

My case Is, i bought 3 books from a vendor which happens to be one of main publisher of our language "malayalam".
As we know, it can only be opened with desired android app. The app is highly ancient and a total mess.

My understanding is that there is a history of Indian language books using non-standard eight-bit character encoding along with custom fonts that predates the use of Unicode.

If that is the case with this book you will need an unencrypted version of the same font used in the published book in order to make it readable.

trysem · 12-02-2022, 10:25 PM

Quote:

Originally Posted by jhowell

My understanding is that there is a history of Indian language books using non-standard eight-bit character encoding along with custom fonts that predates the use of Unicode.

If that is the case with this book you will need an unencrypted version of the same font used in the published book in order to make it readable.

You mean,
The same fonts unencrypted version could be helpful?
Can you elaborate on this?
I am interested in this topic (indian books DRM)
Could you e

12-01-2022, 02:05 PM	#1
trysem Junior Member Posts: 6 Karma: 10 Join Date: Dec 2022 Device: android	how to de-obfuscate fonts in an epub I am new to this field, I have an ebook being purchased, and I want to read it in another reader than the native, but it opens obfuscated. what do I need to do de-obfuscate it? what do I need to have, to deobfuscate? any ID (red somewhere)

12-01-2022, 07:35 PM	#5
KevinH Sigil Developer Posts: 6,693 Karma: 4500780 Join Date: Nov 2009 Device: many	Agreed. Or someone discarded the encrypt.xml from the META-INF folder by mistake as it is needed to tell the reader which fonts are obfuscated. Or manually edited the opf and erased the key identifiers. Last edited by KevinH; 12-01-2022 at 07:37 PM.

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12-01-2022, 03:17 PM	#2
KevinH Sigil Developer Posts: 6,693 Karma: 4500780 Join Date: Nov 2009 Device: many	All valid epub readers successfully handle the de-obfuscation of fonts properly and internally. Trying to copy those fonts out of the epub they were intended for to use in some other epub is the only way you can cause an issue with auto obfuscation and de-obfuscation. Is that what you are trying to do? If so, that is exactly what font obfuscation was meant to prevent.

12-01-2022, 04:52 PM	#3
Quoth the rook, bossing Never. Posts: 6,734 Karma: 55609163 Join Date: Jun 2017 Location: Ireland Device: Both Kinds: epub based makes and Kindle	Either leave it alone or replace the fonts entirely with your own suitable face/style "free fonts" using Calibre Editor Font Manager.

12-02-2022, 10:13 AM	#8
KevinH Sigil Developer Posts: 6,693 Karma: 4500780 Join Date: Nov 2009 Device: many	Changing to a different epub ereader should never require manually deobfuscating anything. The list of obfuscated fonts and obfuscation method is provided by the encrypt.xml file found in the epub's META-INF folder. The data used to obfuscate and deobfuscate depends on obfuscation method and is tied to a specific dc:identifiers in the opf metadata this is sometimes the bookid and another uuid based dc:identifiers. The actually obfuscation algorithm involves a fixed number of bytes (again differs by algorithm) at the top of the font file being xored with data from the opf identifier in a very specific manner. The exact algorithm has been published in the epub spec. But this is not something you can easily manually undo. So as explained earlier, unzip your epub, throw away the broken font files, replace them with known good matching font files (rename exact file if needed), then remove the entire encrypt.xml from the META-INF folder as keeping it will mistakenly cause the reader to obfuscate the font files on load instead of deobfuscating them. Properly rezip up the epub.

12-02-2022, 10:50 AM	#9
trysem Junior Member Posts: 6 Karma: 10 Join Date: Dec 2022 Device: android	The list of obfuscated fonts and obfuscation method is provided by the encrypt.xml file found in the epub's META-INF folder. The data used to obfuscate and deobfuscate depends on obfuscation method and is tied to a specific dc:identifiers in the opf metadata this is sometimes the bookid and another uuid based dc:identifiers. The actually obfuscation algorithm involves a fixed number of bytes (again differs by algorithm) at the top of the font file being xored with data from the opf identifier in a very specific manner. The exact algorithm has been published in the epub spec. But this is not something you can easily manually undo. So as explained earlier, unzip your epub, throw away the broken font files, replace them with known good matching font files (rename exact file if needed), then remove the entire encrypt.xml from the META-INF folder as keeping it will mistakenly cause the reader to obfuscate the font files on load instead of deobfuscating them. Properly rezip up the epub.[/QUOTE] My case Is, i bought 3 books from a vendor which happens to be one of main publisher of our language "malayalam". As we know, it can only be opened with desired android app. The app is highly ancient and a total mess. So first i thought it might some custom DRM or something (actually am not sure). But later on , after surging somewhere like mobileread..etc i found obfuscation. I have seen there, the encrypt.xml, and idpf encryption in it, so i thought it might be obfuscation. Any other reader is throwing error, i cant read.. Please help me if possible......

12-02-2022, 11:32 AM	#10
KevinH Sigil Developer Posts: 6,693 Karma: 4500780 Join Date: Nov 2009 Device: many	If you can unzip the epub and open one of the xhtml/html files in a text editor and it can be read by you, then your epub has no drm and you should do what I said above. If you can not read the text of the xhtml file in a text efitor, then it has drm and we can not help you, as the problem has nothing to do with font obfuscation.

12-02-2022, 01:52 PM	#11
Quoth the rook, bossing Never. Posts: 6,734 Karma: 55609163 Join Date: Jun 2017 Location: Ireland Device: Both Kinds: epub based makes and Kindle	Probably there is also DRM if it only works in the seller's app.

12-02-2022, 03:42 PM	#12
trysem Junior Member Posts: 6 Karma: 10 Join Date: Dec 2022 Device: android	I cant read, Then probably it will be DRM i think.. I think its something custom DRM, any scope in de -DRM? Using any of the tools?

12-02-2022, 05:34 PM	#13
KevinH Sigil Developer Posts: 6,693 Karma: 4500780 Join Date: Nov 2009 Device: many	No idea. Check with the author of the deDRM plugin, not here on mobileread.

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