Super User 
Archive for April, 2011
Compression and Encryption: The ZIP Years.
In a comment to my last post Compression and Encryption, nhinkle asked:
Do you know then how encrypted ZIP files work? Encryption seems to be built into many encryption formats like zip, rar, 7z, etc. Do these usually compress and then encrypt, or somehow do both at once?
Well, ZIP handles this in its own special way. First let’s look at how a ZIP file is made up. A ZIP file consists of one or more ‘file entries’ – blocks of data that make up the actual content of the zip file, followed by a final ‘central directory’:
As you can see each file in the ZIP file has its own local header which contains the information about how the file is compressed. This allows each file in the ZIP file to be compressed in a different way – from “Store” (no compression – ideal for adding pre-compressed files) right up to the maximum and slowest compression available.
April Fools!
Every Friday here at the SuperUser Blog is WTF Friday and what better way to start this one out on April Fool’s.
Super users love a good practical joke. Ever since BOFH came on the scene there have been bids to out-do each other with practical jokes. A while back we were asked what a few of our favorites are, and here some of them are. Since it’s April Fool’s day we hope you find them useful! Just remember that some of these may cause significant problems for people, so use discretion when tricking your friends and colleagues. We don’t want something like this: