zcrypt zip/unzip用暗号化ルーチン
The files described below contain the encryption code for Zip 2.0.x and
UnZip 5.1x (and later). They constitute only an add-on to the exportable
versions (generally named zip201.zip and unzip512.tar.Z) and cannot be
used without the complete Zip or UnZip packages.
This encryption code is not copyrighted and is put in the public domain.
It was originally written in Europe and can be freely distributed from
any country except the U.S.A. If this code is imported into the US, it
cannot be re-exported from the US to another country. (This restriction
might seem curious but this is what US law requires.) However, Phil Katz
has said that he got an export license for his algorithm, so this hassle
of separate distribution may cease one day.