I have a ZIP file, and I want to determine how it was compressed (the specific algorithm, properties used to apply that algorithm, etc.). How can I do this?
zipinfo (from InfoZIP) will tell you a lot about a file.
Sample output from
zipinfo -v (using the "verbose" option
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.
zipinfo functionality is actually part of the
unzip program (the two binaries are usually identical, or links to each other). You can invoke
unzip -Z to get
zipinfo's functionality. So if your installation should not have a
zipinfo binary, you can use
unzip -Z instead.