From: Raph Levien <raph@c2.org>
Date: Thu, 23 Nov 1995 02:50:14 +0800
To: Carl Ellison <cme@TIS.COM>
Subject: Re: Design proposal: crypto-capable generic interface
In-Reply-To: <9511221641.AA14712@tis.com>
Message-ID: <Pine.SUN.3.91.951122094209.29001A-100000@infinity.c2.org>
MIME-Version: 1.0
Content-Type: text/plain


On Wed, 22 Nov 1995, Carl Ellison wrote:

> >Date: Sat, 18 Nov 1995 00:42:21 -0800 (PST)
> >From: Raph Levien <raph@c2.org>
>
> >   I propose that the new interface lives as a sort of daemon, rather
> >than a static collection of command line script pieces. 
> 
> Danger, Will Robinson!  (see below)

   In restrospect, "daemon" was a poor choice of words to describe my
proposal. "Slave process" gets the idea across much better, but may be a
bit less PC. A daemon sits on a publicly accessible port, such as a TCP/IP
socket. The slave process is only accessible to the user who invoked it
(enforced by the OS's file permissions). Further, it only gives secrets to
individual processes that authenticated themselves first (by sending a
passphrase down the connection to the slave process). 

> >   Once the negotation has been established, the application can send
> >the daemon MIME objects that the app does not understand but the
> >daemon does (for example, an image/fractal). The daemon can return a
> >MIME object that the app does understand (for example, an image/ppm).
> 
> This part sounds good...a sort of master translation service.

   I'm glad you like it!

> >   Alternatively, the daemon may request an authentication. This is
> >useful when resolving external bodies that require authentication,
> >including non-anonymous FTP, and standard authenticated HTTP. In this
> >case, the daemon sends a message to the app requesting the
> >authentication. It specifies whether it needs both username and
> >password, or just password. In the latter case, it hands a username to
> >the application.
> >   The application can then query the user for the authentication
> >data. It hands this back to the daemon. In reply, the daemon indicates
> >success or failure. In case of success, it hands the object back to
> >the app.
> 
> Now I get worried.  This communication with the demon is via some IPC --
> maybe even via a LAN.  Some things can't be distributed safely and
> authentication is #2 on my list.

   No, the communication is not via a LAN. On a Unix system, the 
communication is through Domain Sockets. Both processes live on the same 
machine, and the socket "lives" on the local file system.

   I submit that my proposal is every bit as secure as, say, PGP is now. 
If you can't trust the operating system not to hand domain sockets from 
one process to another, then you certainly can't trust it to, for 
example, substitute different binaries for the crypto program (an attack 
which Ian et al cleverly mounted a few weeks ago).
   If it were not the case that my proposal was as secure as PGP, then I 
would want to withdraw it. However, the proposal has so many advantages 
that I would want to see a serious description of the attack, rather than 
just feelings of endangerment to Will Robinson.

> >   Encryption is a bit more tricky, but in essence you just hang a
> >premail-alike off this kind of protocol. The hard part is specifying
> >the key, but you just call it a "parameter" and put in hooks for the
> >daemon to ask for whatever parameters it needs. 
> 
> Crypto keys are #1 on my list of things you can't distribute (unless they
> are wrapped, of course).

   I should have made it cleaer that I am referring to public keys. If 
public keys are on the list of things that can't be distributed, then I 
believe we are in trouble.

> >						 This requires that
> >keys have some nonforgeable names, which is unfortunately not a
> >feature of PGP 2.6.2. S/MIME will do it just fine, if you buy into the
> >Certifcation Authority (<wink> at Nick Szabo).
> 
> Public keys, if that's what you're talking about, have perfectly good
> nonforgeable names -- themselves.  They are unique.  They are the proper
> name which can collect all the attributes of that key which are of interest
> (e.g., permission to spend $, name of a human who knows the private key,
> attributes about that human, etc.).

   Ok. But public keys have one serious disadvantage: their size. I can't 
put a public key on my business card or read it over the phone. I want a 
unforgeable key name. I want this to be the standard key name in the 
interface between the application and the crypto engine. I want users to 
be able to specify them directly, at the very least to bootstrap the 
public key infrastructure.
   I propose using the MD5 hash of the whitespace-free MOSS 
representation of the public key, in hex. It's simple enough to be 
described in one sentence, but does everything I want.

   Note that PGP 2.6.2 does _not_ allow the use of a public key as the 
name of a public key, unless you do a horrible hack such as replace the 
pubring.pgp file with the one public key of interest. This is a 
significant problem when trying to identify which key signed a signed 
message. I haven't bashed around with TISMOSS enough, but I'm not sure it 
will allow this either. I got the impression that it preferred the use of 
an alias.

> >   One final aside: I've been fairly frustrated with this mailing list
> >as a forum for talking about real design proposals and implementation
> >issues. Ignorant posts by the likes of Dr. Fred and Alice d'Clueless
> >tend to attract far more attention than real crypto work. I want a
> >forum for, and just for, cypherpunks who write code. If I had just a
> >smidgen more free time (as if), I'd be trying to start one
> >myself. Anyone else?
> 
> I've seen this happen several times.  As a list gets popular, it
> diversifies.  You might try sci.crypt.research -- since it's moderated.

   Thanks for the suggestion. However, my concerns are with 
implementation and deployment, not research.  I am perfectly willing to 
consider cryptographic algorithms to be black boxes that do what they say 
they will. I think the charter exists to start a new list. John Gilmore 
has already offered to start a "coderpunks" list on toad.com. Shall we 
take him up on it?

Raph