When I was researching old versions of PKZIP, I found that modern unzip programs aren't able to unzip the PKZIP v1.01 distribution file. Three of the member files inside the self-extracting ZIP file fail to decompress correctly. /cygdrive/c/dosprogs/ZIPTEST/101 $ unzip ../DIST/PKZ101.EXE exploding: README.DOC warning: 475 bytes required to uncompress to 873 bytes; supposed to require … Continue reading PKZIP “Implode” compression oddity
Apparently, I'm writing a series of articles about ZIP format. Here's a curiosity. I'm going to use the Info-ZIP zip program to make a ZIP file that the Info-ZIP unzip program cannot unzip. I'll only do things that should be benign, i.e. things that a normal user might conceivably do. This article assumes you have … Continue reading An un-unzippable ZIP file
[2019-09-21: I've edited this document to include some new discoveries.] I already wrote an article about the version history of the PKZIP software, so now it's time for one about the version history of the ZIP format. That sounds like it should be easy, but… not so much. I think the format versions are more … Continue reading Survey of ZIP APPNOTE documents
I wanted to know exactly what versions of the old PKZIP compression software were publicly released for MS-DOS, and some basic characteristics about them, particularly what compression methods they used when compressing files. Sure, Wikipedia has a list, but it wasn't quite what I wanted, and it omitted at least one version I was pretty … Continue reading Survey of PKZIP versions for MS-DOS
I've been researching the version history of PKZIP, the once-popular compression software that gave us the still-popular ZIP file format. There are two important MS-DOS versions of it: v1.10, released in March 1990, which was the latest official version for more than 2.5 years, until v2.04c(?) was released in December 1992.v2.04g, released February 1993, which … Continue reading Will the real PKZ110.EXE please stand up?
The other day, a Twitter user (David Buchanan, @David3141593) posted a message that gained some attention. It has an attached JPEG file, with an image of William Shakespeare. If you save a copy of the JPEG file, and unzip it as if it were a ZIP file, it unzips into the complete works of Shakespeare. … Continue reading About that JPEG/ZIP/Shakespeare hybrid file
The ZIP (PKZIP) compressed file format is organized in a backwards fashion. To unzip a ZIP file, you start by looking for a special byte sequence near the end of it. This is a marker for a data structure (the end of central directory) that points to other data structures that appear earlier in the … Continue reading Corrupting ZIP files