How does one make a Zip bomb?

Question

This question about zip bombs naturally led me to the Wikipedia page on the topic. The article mentions an example of a 45.1 kb zip file that decompresses to 1.3 exabytes.

What are the principles/techniques that would be used to create such a file in the first place? I don't want to actually do this, more interested in a simplified "how-stuff-works" explanation of the concepts involved.

p.s.

The article mentions 9 layers of zip files, so it's not a simple case of zipping a bunch of zeros. Why 9, why 10 files in each?

Answer 1

Tried it. the output zip file size was a small 84-KB file.

Steps I made so far:

1. create a 1.4-GB .txt file full of '0'
2. compress it.
3. rename the .zip to .txt then make 16 copies
4. compresse all of it into a .zip file,
5. rename the renamed .txt files inside the .zip file into .zip again
6. repeat steps 3 to 5 eight times.
7. Enjoy :)

though i dont know how to explain the part where the compression of the renamed zip file still compresses it into a smaller size, but it works. Maybe i just lack the technical terms.

Answer 2

Serious answer:

(Very basically) Compression relies on spotting repeating patterns, so the zip file would contain data representing something like

0x100000000000000000000000000000000000  
(Repeat this '0' ten trillion times)

Very short zip file, but huge when you expand it.