From: Bill Stewart <stewarts@ix.netcom.com>
Date: Tue, 29 Jul 1997 15:59:54 +0800
To: Guillotine <guill@xmission.com>
Subject: Re: New Crypto Application
In-Reply-To: <199707272124.PAA12529@xmission.xmission.com>
Message-ID: <3.0.2.32.19970728081025.00772920@popd.ix.netcom.com>
MIME-Version: 1.0
Content-Type: text/plain



At 03:24 PM 7/27/97 -0600, Guillotine wrote:
>I'm creating a new _text_ cryptography program.  

What do you mean by "text cryptography"?  You'll only accept text as input,
or you'll produce your output in ASCII, or you'll produce your output
as English-like words?  None of the common encryption algorithms treats
text input any differently that raw bits, and it's worth taking whatever
input you have and compressing it to reduce the amount of data the
encryption and transmission phases need to handle.  Producing printable
ASCII as an output format isn't a cryptography issue - it's just a 
simple reversable transform from a bunch of raw bits to printable,
and there's no excuse for inventing a new format rather than using
MIME encoding, uuencode, or btoa, unless you're doing something extremely
creative with Unicode...  

Producing output as English-like words is more interesting.
It's a steganography issue, not a cryptography issue, since you should
be doing the secure part first anyway, but it can be useful for
obscuring the fact that you're using crypto in a message.
The canonical reference is to Peter Wayner's Mimic Functions,
which let you model an arbitrary context-free grammar for output,
but you should also look around for "texto".  (The other canonical
reference is to "PHB", Dilbert's program that disguises the message
in Pointy Haired Boss jargon, but I'm not aware that anyone's written it.)

A good book to read on cryptois Bruce Schneier's "Applied Cryptography",
which discusses most of the current algorithms and how they're used.
>The encryption algorithm,
>using a symmetrical is going to be as strong as legally allowed, 

There are no legal restrictions on cryptography strength in the US;
only restrictions on what's exportable, and even then you need permission. 

#			Thanks;  Bill
# Bill Stewart, +1-415-442-2215 stewarts@ix.netcom.com
# You can get PGP outside the US at ftp.ox.ac.uk/pub/crypto/pgp
#   (If this is a mailing list or news, please Cc: me on replies.  Thanks.)