How to create minimum size (empty) zip file, which has 22B?

Question

I´m trying to solve some security problem with file, whose MD5 hash is 76cdb2bad9582d23c1f6f4d868218d6c.

I don't have that file, but based on internet MD5 searches, I think, it is minimum size zip file. I found one example and its content is exactly same like minimum size zip file.

Is it possible to create such minimum size zip file (22 B) with Linux (or Windows) command?

BTW: Recently, I solved similar task with gzip file: gzip -n EmptyFileName

Solution 1

Here you go:

50 4b 05 06 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00

That has the MD5 signature you provided.

If you have Info-ZIP's zip, you can create it thusly:

zip empty.zip anyfile
zip -d empty.zip anyfile

That adds "anyfile" to a new zip file, and then deletes it from the zip file, leaving it empty.

Solution 2

An easier-to-use version for copying-and-pasting into the shell:

echo UEsFBgAAAAAAAAAAAAAAAAAAAAAAAA== | base64 -d > empty.zip

This just prints the base64'd version of the empty zip file (created by creating a zip file with a single file then deleting that single file from the zip file), and reverse the encoding with base64 -d and writes the output to empty.zip.

---

If the version of base64 that ships with your machine doesn't use the same syntax as above, here's a more-portable but less-terse alternative:

echo UEsFBgAAAAAAAAAAAAAAAAAAAAAAAA==  | openssl enc -d -base64 > empty.zip

Solution 3

With Info-Zip (standard zip/unzip installation on Ubuntu 20.04), you will have to use the -i "*" option. If it's not present, zip will complain and exit with error code 1 on creation. Counter-intuitively, its behaviour changes with -i "*".

mkdir /tmp/mytest
cd /tmp/mytest
zip -r mytest.zip . -i "*"

mytest.zip will be the empty zip file you desire.

Solution 4

with this .bat script you can create empty.zip file under windows:

@echo off

del /q /f empty.zip >nul 2>nul
certutil -decode "%~f0" empty.zip

-----BEGIN CERTIFICATE-----
UEsFBgAAAAAAAAAAAAAAAAAAAAAAAA==
-----END CERTIFICATE-----

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Comments

[Yona Appletree]

Arguably, directly echoing the bytes to a file is a simpler method of creation: echo -n '\x50\x4b\x05\x06\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x0‌​0\x00\x00\x00\x00\x0‌​0\x00\x00' > empty.zip

[Mark Adler]

Matched for me. Might depend on your shell.

[Mark Adler]

I had to use -D instead of -d on my system. You can use echo -n to avoid the newline, however you don't need to. Just use echo. base64 doesn't care about the newline.

[harry]

@MarkAdler Thanks. echo -n isn't portable, but I completely forgot that base64 doesn't care about line endings. I'm not sure what's the most portable way of doing base64 decode, perhaps via openssl but that's not available oob on macOS any longer, I think.

[Mark Adler]

I have the latest macOS, and the openssl command from LibreSSL 2.2.7 is there. It also has base64.

[Tom Cornebize]

@MahmoudAl-Qudsi It works with zsh. With bash or sh, you have to add the -e option: echo -ne '\x50\x4b\x05\x06\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x0‌​0\x00\x00\x00\x00\x0‌​0\x00\x00' > empty.zip

[harry]

Thanks, @MarkAdler; added an openssl-based variant to the answer.