
You can find what you're looking for on hundreds of sites worldwide.  Try

	anonymous ftp to nic.funet.fi (Finland)

	/pub/unix/4.3bsd/net2/lib/libc/gen/crypt.c.Z

This includes source code for fully-functional DES encryption and decryption.

There are some who believe that public domain code is exportable, some
who don't.  Make your own judgements, but it seems obvious to me.