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Glossary

What is font obfuscation?

Updated:

Font obfuscation is a simple scrambling of embedded font files, keyed to the EPUB's unique identifier and declared in META-INF/encryption.xml, so a font cannot be copied out of the ZIP and installed elsewhere. EPUB 3.3 says it is not encryption and offers no real protection.

Why it matters when you convert a PDF to EPUB

It exists because some font licences allow embedding only if the font is tied to the book. It matters when you edit or rebuild an EPUB: changing the unique identifier breaks obfuscated fonts, and obfuscating anything that is not a font is an error.

EPUBCheck reports a non-font file listed as obfuscated with PKG-026, and its usage message OBS-001 can name font obfuscation as an outdated feature.

How EpubCC handles it: the engine embeds no fonts, so there is nothing to obfuscate and its EPUBs have no encryption.xml. The reader's own fonts are used instead.

Related terms

EPUBCheck messages about this

  • PKG-026 Obfuscated resource must be a Font Core Media Type (was declared as "…" in "…").
  • OBS-001 Usage of … is outdated.

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FAQ

What is font obfuscation?

Font obfuscation is a simple scrambling of embedded font files, keyed to the EPUB's unique identifier and declared in META-INF/encryption.xml, so a font cannot be copied out of the ZIP and installed elsewhere. EPUB 3.3 says it is not encryption and offers no real protection.