How can I make a v1.0 zip archive, so that when ran against file returns
Zip archive data, at least v1.0 to extract
When I create a zip file with the zip command line utility or Xarchiver, file returns
Zip archive data, at least v2.0 to extract
You can create version 1 ZIP archives using Info-Zip’s zip 1.1, which is still available (download zip11.zip). You’ll need to build it from source (make sysv on a Linux system); then you’ll be able to use the newly-built zip to create old-format archives:
$ ./zip -9 test.zip zip.c
adding zip.c (imploded 70%)
$ file test.zip
test.zip: Zip archive data, at least v1.0 to extract
$ unzip -v test.zip
Archive: test.zip
Length Method Size Cmpr Date Time CRC-32 Name
-------- ------ ------- ---- ---------- ----- -------- ----
25825 Implode 7749 70% 10-21-1991 13:33 e1f47bfc zip.c
-------- ------- --- -------
25825 7749 70% 1 file
This uses the “implode” or “shrink” algorithms for compression (it uses whichever is better with any given file), rather than the “deflate” algorithm used in version 2 of the format.
It seems that the v2.0 zip utility was the first to support compression. Zip archives that require 'at least v1.0 to extract' can be created by passing -0 (no compression) to the zip utility.
You can directly modify the magic byte of the zip file that identifies it as a v2.0 zip file:
$ file foo.zip
foo.zip: Zip archive data, at least v2.0 to extract
$ printf '\x0a' | dd of=foo.zip bs=1 seek=4 count=1 conv=notrunc
1+0 records in
1+0 records out
1 byte copied, 9.7214e-05 s, 10.3 kB/s
$ file foo.zip
foo.zip: Zip archive data, at least v1.0 to extract
$
I found the byte's value (0x0a) and location (4th byte) to change by looking up the source for file:
$ apt-get source file
$ grep -R 'at least v1.0'
file-5.30/magic/Magdir/archive:>>>4 byte 0x0a \b, at least v1.0 to extract
You might corrupt your zip file, but file will report what you want.
