DES encryption algorithm

[Joshua Muskovitz]

> > 1: Has any pure python algorithm been implemented already?

I ported my ex-companies C implementation of DES to Python.  I made a first
pass just porting function by function.  This was the easiest solution,
since it made unit testing of each function much easier.  I also refactored
the code as I went, inlining functions that were really only called in one
or two places.

One thing that will bite you in the ass is that python bitwise right shift
is *sign extended*, so you can't just use >> in your bit twiddling.  This
was the bug that took the longest for me to find.

Here is a handy function for handling right shift.  Replace all occurrances
of x >> y in your code with rshift(x, y).

def rshift(num, dist):
    if dist == 0:
        return num
    else:
        return ( (num >> dist) & (0x7fffffff >> (dist-1) ) )

--
# Joshua Muskovitz
# joshm at taconic.net
def lyyrs(sig): return '-'.join(sig.split()+["ly y'rs"])
lyyrs('Hire me!  I need the work!')




-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----==  Over 80,000 Newsgroups - 16 Different Servers! =-----