Subject: Re: Location and Identification

From: "Bob Jueneman" <[email-masked]>
Date: Fri, 19 Mar 1999 14:19:09 -0700

Tony, just a couple of observations.

With regard to location, although there certainly will be completely
proprietary, closed-PKI systems, and probably some global-public
directories also, the most interesting cases are going to be the
in-between ones.

I can certainly imagine a case where a company has its corporate 
directory servers located inside their firewall, but certain portions of 
their directory will be replicated to public servers located outside 
the firewall.  In fact, I expect this case to be quite common within
the next few years, and that is why I've been trying to focus on 
how to find those directories.

With respect to the biometric identifiers, my assumption is that 
if these mechanisms are to be at all useful for use at a distance
(as opposed to at an ATM machine, for example), the biometric 
template must be public, in the same sense that a public key is
public.

But in order to make this at all feasible, it is ESSENTIAL that the 
transformation from the recorded biometric indicia produce a
one-way mapping to the template, so that the biometric 
measurement itself cannot be compromised.  

In other words, given the template, it must be computationally 
infeasible to produce some biometric indicia, either real or
artificially constructed, that would satisfy the template.

Although you might include a JPEG photo of the user in the 
certificate for comparison at a point of sale terminal, you 
certainly wouldn't want to include a JPEG copy of your
fingerprint, nor a digitized copy of your handwritten signature,
because of the obvious ease with which that data could be 
extracted and used for some other purpose.

Bob

>>> Tony Bartoletti <[email-masked]> 03/18/99 05:47PM >>>
Bob,

I am a bit reticent to jump into the threads with this, but I offer
it to you to use as you wish (forward, edit, consider, whatever.)
My thoughts here are in response to several recent threads.
 
I don't pretend to know the intimate details of DNs, AltNames, etc.,
(collectively "Name-Like-Things") and the precise handling expected
of them by X.509-conforming software.  Nor am I expert at the varied
contents (keys, et al) that may be bound into the certificates,
(collectively, "Ident-Challenge-Data").

I see from these discussions at least two broad and (in my ideal)
orthogonal dimensions that people intend for them to serve:

1.  Location (of individual/cert or their issuer)

    Ranging from Global-Public-Location to Proprietary-Location

2.  Secured Identification (of located item.  "Ident-Challenge-Data")

    Ranging from Public/Private Keys to Biometric Data.

I think it is useful to consider this (simplified) "quad-chart"
and characterize various schemes/applications accordingly:

  FUNCTION:    |  Object Location         | Object Identification
  METHOD:      |  (via Name-Like-Thing)   | (via Challenge-Data)
  ---------------------------------------------------------------
  (subclass)   |  Global Public Locator   | Keys/Issuer-Keys
  ---------------------------------------------------------------
  (subclass)   |  Proprietary Locator     | Biometric Data/Hash
  ---------------------------------------------------------------

Note:  I do not intend for these "rows" to indicate correspondence.
That is, one could deploy a system where a "Proprietary Locator" is
used to retrieve "Keys/Issuer-Keys" Challenge-Data, (basically, the
current situation with key-certificates) or (God Forbid) a system
where a "Global Public Locator" can retrieve an individual's
Biometric Challenge Data.

Furthermore, in each possible case, one can imagine a protocol
that either does or does not require the "data-owner" to cooperate
in the final step of identification (say, you believe you have
located someones challenge-data, but can only see a piece of it
large enough to query them to release the remainder, and can
then proceed with a full challenge if they concur.)

This is how the telephone white-pages work.  If I find (say) three
"Bob Jueneman" I can call each one.  If I say "Are you the Bob that
posts to the PKIX list," you can either reply with additional
confirming data, or say "Sorry, this is Jueneman's Plumbing Supplies,
we only carry PVC, no 'PKIX'" just to avoid me.  

If I may characterize the discussions of late, I see some threads
hoping to elevate (?) Proprietary Locators to Global Public Locators,
(Simon says, "Lets build the X.500 directory of Babel") and others
to extend certified content from Keys to Biometrics, for instance.

Worse, I also see a blurring of the functions themselves, to wit,
"Let a secure directory hold established name-hierarchies that map
precisely to the material world, thus Existence-In-Directory
implies Identification, (delete one challenge-response.)"
       
As sexy and convenient as it may seem to overload these functions,
especially Location with Identification, such a scheme would be
both unstable and dangerous (the ultimate bad combination).

When someone says "We can make the directories secure" I cringe.
How secure?  For what?

The public telephone white-pages are secure enough for their purpose;
if a hacker or insider makes malicious modifications, it is just an
inconvenience for the most part.  If a directory holding my keys
is compromised, more hassle, but I can revoke and be re-issued.

I don't know if nature allows a directory secure enough to house
my biometric data, unless it is purely encrypted blobs to the
root directory operators, and I have secure control of the keys.

A Final Thought:  I am beginning to wonder if I should start a
global movement to have everyone capture all of their biometric
data (fingerprints, retinals, DNA sequences, etc) and publish
them in a giant, open public repository.  Would this not serve
make such data effectively worthless?  The only way this data
can be used to effectively "impersonate" me, is if there is a
reasonable assumption on the part of the relying party that
such information is uniquely held.  Destroy this assumption,
and the ability to impersonate disappears, no?

___tony___

Tony Bartoletti                                             LL
Center for Information Operations and Assurance          LL LL
Lawrence Livermore National Laboratory                LL LL LL
PO Box 808, L - 303                                   LL LL LL
Livermore, CA 94551-9900                              LL LL LLLLLLLL
phone: 925-422-3881   fax: 925-423-8002               LL LLLLLLLL
email: [email-masked]                                   LLLLLLLL

---

From: Tony Bartoletti <[email-masked]>
Date: Fri, 19 Mar 1999 17:31:18 -0800

>Tony, just a couple of observations.
[snip]
>template must be public, in the same sense that a public key is

Odd.  I think of an ATM machine as "at-a-distance", since the
local input must be compared to something stored "far away".
Perhaps your intent is to say that the "data-capture" system,
being embedded in the guts of the armored ATM machine, cannot
thus be spoofed at the point-of-capture.

My point is, I imagine 10 years from now, one could easily create
a "glove" with another persons fingerprints using photo-lithography
and latex, given the fingerprint images.  I know there are other
technologies to help prevent this (temperature, surface capilliaries)
but then just wait a few more years...

>artificially constructed, that would satisfy the template.

I'm not certain of the definition of "template" in this context.
I imagine taking a "heuristic-hash" of my thumbprint.  That is,
the "hash algorithm" is public, one certainly cannot begin with
the "hash" and thus construct "fingerprint data" (one way), and
yet slightly distorted images of my thumbprint will still yield
(effectively) the same hash.  Is this the gist of it?
 
>extracted and used for some other purpose.

Well, my fear is that it will become trivial to "lift" prints
from, say, soda cans.  If I place a poster on a bulletin
board in a supermarket, with big print that says WARNING,
followed by print underneath so small that people will have
to come up close to read it, then I can embed a tiny camera
behind a tiny hole in the poster, triggered by one of those
tiny radar-proximity chips, and thus capture retinal data.

Most important, we often seem to design systems to protect
us from the 98% of us who are already honest enough not to
cheat us, and inadvertantly strengthen the hand of those
sophisticated criminals who will spoof authentications
and thus be judged more solidly "authentic" in the process.

Out of curiosity, what do you think would happen if everyone
posted crisp images of their fingerprints and retinas to
the usenet newsgroup "alt.kill.biometrics"?

Of what use can it be to have another's fingerprints if it
is assumed that anyone can spoof them?

(There is no such newsgroup, but I might start one;)

___tony___

Tony Bartoletti                                             LL

---

From: Stephen Kent <[email-masked]>
Date: Sun, 21 Mar 1999 20:28:43 -0500

Bob,

>artificially constructed, that would satisfy the template.

As I mentioned in a private note to Bob, my experience with biometric
templates suggests that it is generally NOT possible to store templates in
this fashion.  The reason is that the matching algorithm for a biometric
must take the captured data and score it against the template.  Since the
captured data will almost alwways be a little "off," one needs to be able
to determine how far off the data is.  A good hash function defeats this
purpose, e.g., a single bit error is a distant (hamming distance) as a
multi-bit error.

Steve