"encrypt tcp connections" hacks

Perry E. Metzger perry at imsi.com
Sun Feb 5 18:03:00 PST 1995

strick at The Yak says:
> I take your opinions more seriously than perhaps I should,

I don't want to scare people into not doing things -- but I do want to
inform. Persons taking my opinion, or that of any authority, on face
value without doing their own reasoning, get what they deserve.

> I'm not doing this to re-invent the wheel.  I'm doing it because
> I need it, and nothing else is working very well for me.

Then do it...

> I'm doing it because I don't see anything that's easy-to-use in wide
> use today.  I don't just want one or two encrypted applications -- like
> the Kerberos telnet and rcp -- but something to transparently provide
> privacy for all TCP sockets -- like SMTP sockets between (re)mailers,
> NNTP, X11, FTP, MUDs, etc.

Well, in the long term, my hope is that people use IPSP for this. It
will mean that the kernels on their machines simply deal with all this
stuff and that userland applications get to ignore it 90% of the time.

> Let me name the ones I can think of.
>   1.  	Matt Blaze just announced one.

>   2.	Kerberos4.  I use Kerberos4 between home and work all the time.
> 	However the only command I have that actually encrypts the
> 	session is the "rlogin" replacement.

And the telnet; however, it has a library to let you do whatever you want.

>       (But I sure use it, even if it's just DES.)

In v5 there is more general support, I believe.

> 	Also Kerberos administration is a nightmare.

Thats really an interface issue, I think -- they have a lot of the
fundamental stuff down. If thats one's only complaint with Kerberos (I
have others) the "right thing" is to build a simplified administration

> 	And the reason big providers like The Well and Netcom won't
> 	run kerberos (or at least not the last time I asked) is that
> 	they would have to hire another person just to do the
> 	password management etc.

Thats quite untrue -- passwords in kerberos are set by the users, not
by the administrators!

>   3.	Kerberos5.  I've been unable to build Kerberos5 on my 
> 	sun3.  Honestly.  To build it, I have to have ISODE, which seems 
> 	to be some enormous ISO thing that I haven't been able to build.
> 	Again, not too encouraging for your average unix sys admin.

You only need ISODE for the ASN.1 compiler; you don't have to build
the whole thing.

>   5.	Standards for IPng.  Vapor, as far as I know.  Is there any
> 	usable code, that works in IP this generation?

There is swIPe, and the derived TIS product. Its a bit primitive since
it doesn't handle per-socket keying. There is stuff that I'm hacking
on between flames -- its going to be called swIPe II. It will conform
to my RFC drafts and should run out of the box on any 4.4BSD
system. I'm hoping people will back-port it to SunOS and the like.

There is also SSL, which is what the Netscape people are pushing --
stands for Secure Sockets Layer.

There is also the thing this guy Andy Heffernan did a draft on in
which you do this at the TCP layer; he uses a TCP option to pass IVs
and MACs.

There is also the method proposed by the AFT working group at the
IETF, a.k.a. the "socks" working group, for encrypting sockets.

There is also the thing that Miron Cuperman wrote for YTalk. It did
diffie-hellman key exchange followed by an encrypted session.

There are about three or four more that I can't bring to mind at the
moment but I'm damn sure I've seen them.

> I think it comes down to the fact that, of these, only Skronk and 
> Blaze's software use a Diffee-Hellman -like Key Exchange so that
> administration stuff doesn't have to be done by humans and footnet.

Diffie-Hellman doesn't give you real security without some sort of way
to authenticate the exchange. Man in the middle gets you. You are then
down to either using signed exchanges or some sort of challenge or
conventionally keyed way of authenticating.

BTW, Kerberos most emphatically does not require active
administration. I've run it in an environment with thousands of hosts
with narry a person paying it any attention.

> The real value I'm adding is not the crypto.  It's the packaging.
> When I'm done it should be possible to skronk all your current 
> clients and servers by just overriding the shared library libc.so,
> running a skronk map UDP daemon, and customizing a configuration
> file to tell the daemon what to say.

Well, this is an admirable goal. Of course, the Netscape people want
to do the same thing with SSL, and others have proposed to do it, too.

Ultimately, the thing that is going to fix the net is IP layer
encryption -- anything at a higher layer can't really fix all the
problems reliably. (As an example, consider RST attacks against TCP
connections.) It also can't fix them pleasantly.

Meanwhile, of course, it is going to be a while before that stuff is
universally deployed. My reference implementation isn't going to be
here before April. It will be freely available, but it will only run
on some architectures, and it is unlikely to be idiot friendly or
perfect out of the box day one.

Understand, also, that as one of the few people here who writes code I
don't want to discourage you from continuing by any means!

However, I'd say that this isn't going to be a permanently deployed
thing on the net -- that much we can be pretty sure of.

> The discussion question is -- if we have so many hacks already -- 
> howcome they're not in use.

Probably people aren't that enthusiastic about them. Encrypted
sessions are in wide use for telnet and the like -- I do that sort of
thing regularly, and now that session stealing has become a fact of
the net I suspect that S/Key is going to vanish and be replaced by
various encrypted telnets. SMTP it doesn't make much sense to protect
because what you really want to protect is the contents -- i.e. via
PEM, MIME security multiparts, or some similar method (I favor PGP'ed
secure multiparts myself.)

> p.s.	need some wizard-level help here.
> 	I use syscall(2) when I reimplement read() write() connect()
> 	accept() etc. on SunOS. 

Why? Why not just do the original calls? If you are trying to overlay
shared libraries, just rename the calls in the symbol tables or
relink the library or something similar...


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