Detecting ZLIB Compression

In diary entry "Recognizing ZLIB Compression", I mention my tool it's mainly a wrapper for command file (libmagic).

By default, command file has no definitions to detect ZLIB detection, but my tool uses an additional file with custom definitions:

Take for example a ZLIB compressed stream in a PDF document:

As you can see, the stream starts with 0x78, an indication that this is ZLIB compression.

Piping this stream in my tool helps identifying the unfiltered stream content:

Of course, if you don't want to use this tool, you can just integrate these ZLIB definitions in your own definition files.

Didier Stevens
Senior handler
Microsoft MVP


677 Posts
ISC Handler
Aug 4th 2019

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