Subject: RE: Current signature formats insufficient

From: Adrian McCullagh <[email-masked]>
Date: Thu, 13 Jul 2000 12:05:59 +1000

Tony

I apologise to everyone for the length of this response.

The objective test that I mentioned is in fact the position of a reasonable
person.  That is what is reasonable in the circumstances.  Only the facts in
the case will determine this.

The real problem as I see it is that a person who has been attributed as
having digitally signing a digital document could claim that the digital
signature is theirs and was affixed by them but it was not their act.  This
is different to a forgery case as in such cases the digital signature may
have been generated by a key that corresponds to their private key but was
generated through the act of a third party.  That is, the third party has
acquired through some means a copy of the private key of the alleged signer.
Hence a forged digital signature. 

The issue that I am raising in legal terms is called "Non Est Factum" - "not
my act".  

The legal case books have numerous examples of cases involving the issue of
Non est Factum.

The best way to describe it is by drawing upon a real case that occurred in
Australia.  I understand that the law in this case corresponds to US,
Canadian and UK legal principles.

The Facts:
==========

Mr & Mrs Almedio were 2 elderly Italians that lived in Sydney.  Their son
was a business man whose business was having difficulties and as such his
Bank was pressing for more collateral security.  The son who grew up in
Australia was fluent in Italian and in English.  His parent could only speak
a little English and could not read English at all. (You wonder how they
survived for over 20 years in a predominately English speaking country).

Now the son was asked by the Bank to get his parents to guaranty an
extension to his current loan facility.  The son went to his parents and
presented to them the guaranty document.  The guaranty was to cover the full
amount of the loan and not just the extension.  His parents could not read
the document and were advised by the son that the document was to secure the
extension of $50,000.  The full extent of the loan facility was in excess of
$500,000.

In effect the parents were signing a document without understanding what
they were signing and had no way of understanding as they could not read the
document. They were relying on and trusting their son as regards to the
contents of the document.

Obviously, the son's business went into liquidation and the Bank tried to
rely on the guaranty that had been signed by the parents.  There was no
dispute as to the authenticity of the signatures.  The parents relied on the
lack of intention to sign the document as regards to it true effect. In
effect, they argued successfully that it was not their act. They lacked the
necessary intention.  Now the evidence to support such a case is extensive.
It is not an easy case to prove.

End Case
========

By analogy, this is what could happen when signing a digital document.  The
actual signing mechanism is a black box and hopefully what is actually being
signed in memory corresponds with the human readable display on the screen.

Now the next issue is what evidence will the signer need to successfully
support a claim of non est factum. I have not analysed this thoroughly but
it is an issue that needs to be addressed. The answer may be in the security
classification of software where there may exist a trusted path between the
memory where the document resides and the display screen and the key board.
This is highly unlikely to occur as it would, I think, require a
re-engineering of the current versions of the popular commercial Operating
Systems.  

Without a trusted path the signer will not be in a position to adequately
know what is being signed.  

I think what needs to be done is for the digital signing of document be
mapped out so that the necessary evidential issues are addressed.  This will
permit a court to have confidence in the technology and thus be in a better
position when it comes to a dispute.  Also the current digital signature
legislation apart from Germany totally ignores the trust required in the
signing mechanism.  In Germany the signing component must be classified to
at least ITSEC E4 (Common Criteria EAL 4) but ITSEC as has been identified
previously on this list does not address the crypto module.  So Fips 140-1
should be used.

The UTAH Dig Sig Act deals with trustworthy systems at the CA level.  Now
the CA has nothing to do with the signing of documents.  The CA at best will
store public keys that are used for the verification of signatures not the
affixing of signatures.  Really a post event analysis.

A further complication is that in many cases the onus of proof concerning
the authenticity of the digital signature will reside with the relying
party.  But that is another issue.

Adrian McCullagh
Director of Electronic Commerce		Tel: 617 3231 1522
Gadens Lawyers					Fax: 617 3229 5850	
level 39
Central Plaza 1
345 Queen Street
Brisbane Australia 4000

Ph. D. Candidate 
Thesis "The Incorporation of Trust Strategies in Digital Signature Regimes
for Elec. Comm."
Information Security Research Centre
Queensland University of Technology

---intentionally deleted material---

There are limits to the courts reliance on a purely objective view.
The courts tend to consider what must also be "reasonable."

If I were a pizza delivery person, and I'd crafted an ordinary-looking
receipt, whose fine print on the back reads "I hereby transfer title
to my house ...", I doubt that your signature on that receipt will
enable me to take your house from you.

Most of the "real" legal questions with digital signatures and our
new "cyber" environment will pivot upon the evolving problem of
deciding what are "reasonable expectations", given the technology
and other, less objective considerations.

___tony___

Tony Bartoletti 925-422-3881 <[email-masked]>
Information Operations, Warfare and Assurance Center
Lawrence Livermore National Laboratory
Livermore, CA 94551-9900

---

From: "Simon McMahon" <[email-masked]>
Date: Thu, 13 Jul 2000 14:41:15 +1000

Adrian wrote :
[snip]
> The issue that I am raising in legal terms is called "Non Est Factum" -
"not
[snip]

A great argument for certified signing devices but they cost a lot to
create, or at least now they do because volumes aren't high enough. There
will still be demand for low cost signing devices (hackable PCs with
uncertified software and SCs).

I dont see what this has to do with signature formats however, although I
agree its an interesting and important issue.

Surely in the case you cited the Alememdios' signatures would have been
witnessed by representatives of the bank and they should have made sure the
Alemedios understood what they signed by supplying their own translator. I
guess thats why the Alemedios won.

My point is that witnessing is the right way to boost non-repudiation (that
failed in this case) to a level where big dollars are involved. Non
witnessed signatures, standard or digital, must therefore be more vulnerable
to repudiation claims. A digital witness would need to assure that the
witnessed signature was made with a trustworthy signing device and that the
signer understood what was being signed.

I can concieve of a trustworthy signing device, not at home but at a bank
branch or kiosk, that accepts a smart card with my private key on it.
Authenticates me and makes me say 'Y' to "do you understand and wish to sign
what you have read above ?" (wherever "above" happens to be) and then
applies my signature. It then counter signs my signature with its private
key which the RP can recognise as that of a trusted device. The RP may not
know for sure that I actually understood what I was supposed to have read,
only a human witness, in my opinion could do that, but the RP has high
assurance that the signature is not the result of a hacked PC with an SC
reader.

Simon McMahon

---

From: Tony Bartoletti <[email-masked]>
Date: Thu, 13 Jul 2000 10:56:48 -0700

>signer understood what was being signed.

I agree.

>assurance that the signature is not the result of a hacked PC with an SC

Now, I'm thinking of a protocol where (again from a trusted installation
such as a kiosk) once you supposedly have read the "terms of agreement",
the process walks you through several, randomly generated multiple choice
questions regarding these terms, presented in random order.  Failure to
get 100% on this "quiz" takes you back to the screens to review the terms.
Success on this quiz is digitally certified and accompanies the signed
agreement.

This (though a bit awkward) would make it considerably harder to claim
"I didn't understand what I was signing."

___tony___