What encryption algorithm is used by linux's 'zip' command?

Question

I'm aware that the default encryption provided by the zip command in Linux isn't considered to be secure, but I'm curious - what algorithm does it use when encrypting with the --encrypt option?

Solution 1

Since the zip command will write out PKZIP files, it would follow they're implementing the specs for that. Apparently the format allows for several distinct ciphers, the one typically considered "insecure" looks like it's homegrown.

See here for a detailed discussion of how to break it, including some insights into the original algorithm: http://math.ucr.edu/~mike/zipattacks.pdf

Solution 2

Traditional encryption is based on a stream cypher by Roger Schaffely. The exact, symmetric algorithm is illustrated here http://www.academia.edu/348210/PKZIP_Algorithm

Newer versions of the linux zip utility (zip-info) seem to be going to include AES encryption aswell: http://www.info-zip.org/phpBB3/viewtopic.php?f=4&t=396&p=2453&hilit=aes#p2453

Comments

[Marc B]

Same as any other zip: en.wikipedia.org/wiki/Zip_%28file_format%29#Encryption

[Pierz]

The algorithm used may be displayed using 7zip: 7z l -slt file.zip