PaddingZip is a tool that you can craft a zip file that contains the padding characters between the file content.
A normal zip file:
A craft but valid zip file:
For example, you can craft a valid JAR file using PaddingZip:
Usage
$ python paddingzip.py -h
usage: paddingzip.py [-h] -i INPUT_FILENAME -o OUTPUT_FILENAME [-p PREPEND] [-a APPEND]
A tool that you can craft a zip file that contains the padding characters between the file content
optional arguments:
-h, --help show this help message and exit
-i INPUT_FILENAME, --input INPUT_FILENAME
-o OUTPUT_FILENAME, --output OUTPUT_FILENAME
-p PREPEND, --prepend PREPEND
the characters that you want to prepend to the file beginning
-a APPEND, --append APPEND
the characters that you want to append to the file
For example:
python paddingzip.py -i original.jar -o modify.jar --prepend "this prepend to the start" --append "this append to the end"
zip -F
You also can use zip -F to fix the offset:
$ echo -n "prepend" > f
$ cat f a.zip > b.zip
$ zip -F b.zip --out c.zip