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I have a ZIP file, and I want to determine how it was compressed (the specific algorithm, properties used to apply that algorithm, etc.). What software can do this for me?

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2 Answers 2

up vote 5 down vote accepted

zipinfo (from InfoZIP) will tell you a lot about a file.

Sample output:

Archive:  /tmp/test.zip
There is no zipfile comment.

End-of-central-directory record:
-------------------------------

  Zip archive file size:                     22341 (0000000000005745h)
  Actual end-cent-dir record offset:         22319 (000000000000572Fh)
  Expected end-cent-dir record offset:       22319 (000000000000572Fh)
  (based on the length of the central directory and its expected offset)

  This zipfile constitutes the sole disk of a single-part archive; its
  central directory contains 1 entry.
  The central directory is 88 (0000000000000058h) bytes long,
  and its (expected) offset in bytes from the beginning of the zipfile
  is 22231 (00000000000056D7h).


Central directory entry #1:
---------------------------

  tmp/bookmarks.html

  offset of local header from start of archive:   0
                                                  (0000000000000000h) bytes
  file system or operating system of origin:      Unix
  version of encoding software:                   3.0
  minimum file system compatibility required:     MS-DOS, OS/2 or NT FAT
  minimum software version required to extract:   2.0
  compression method:                             deflated
  compression sub-type (deflation):               normal
  file security status:                           not encrypted
  extended local header:                          no
  file last modified on (DOS date/time):          2010 Feb 20 16:22:48
  file last modified on (UT extra field modtime): 2010 Feb 20 16:22:47 local
  file last modified on (UT extra field modtime): 2010 Feb 20 15:22:47 UTC
  32-bit CRC value (hex):                         3e84c75c
  compressed size:                                22155 bytes
  uncompressed size:                              76774 bytes
  length of filename:                             18 characters
  length of extra field:                          24 bytes
  length of file comment:                         0 characters
  disk number on which file begins:               disk 1
  apparent file type:                             text
  Unix file attributes (100600 octal):            -rw-------
  MS-DOS file attributes (00 hex):                none

  The central-directory extra field contains:
  - A subfield with ID 0x5455 (universal time) and 5 data bytes.
    The local extra field has UTC/GMT modification/access times.
  - A subfield with ID 0x7875 (Unix UID/GID (any size)) and 11 data bytes:
    01 04 e8 03 00 00 04 e8 03 00 00.

  There is no file comment.

If that is not enough, please explain which information you need.

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This looks like what i need, but InfoZip's mirrors appear to be down and only the source is available at sourceforge... –  RCIX Mar 16 '10 at 0:21
    
Ok, i figured it out. I first followed their FTP instructions (with a slight modification), but then i found you can grab what you need from ftp.info-zip.org/pub/infozip/win32 . –  RCIX Mar 16 '10 at 4:08
    
Sorry, i still need help: zipinfo doesn't appear in the archive i downloaded :( –  RCIX Mar 16 '10 at 7:40
    
@RCIX: Sorry, no idea where you can get Windows binaries. I use Linux, where it's part of all distributions :-). Just post a new question to ask about windows binaries. –  sleske Mar 16 '10 at 9:46

The zipinfo command can actually be run on windows by using "unzip -Z" command, as stated in the info-zip archive's documentation. Make a "zipinfo.bat" batch file with this command inside:

unzip.exe -Zsvh %1

and you have zipinfo running on windows.

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1  
This command works on CentOS/Linux too, obviously after removing .exe –  Aditya Kumar Pandey Jun 26 '13 at 12:44

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