dual-use digital signature vulnerability

[Anne & Lynn Wheeler]

At 08:25 AM 7/19/2004, Jerrold Leichter wrote:

>A traditional "notary public", in modern terms, would be a tamper-resistant
>device which would take as inputs (a) a piece of text; (b) a means for
>signing (e.g., a hardware token).  It would first present the actual text
>that is being signed to the party attempting to do the signing, in some
>unambiguous form (e.g., no invisible fonts - it would provide you with a
>high degree of assurance that you had actually seen every bit of what you
>were signing).  The signing party would indicate assent to what was in the
>text.  The notary might, or might not - depending on the "means for 
>signing" -


note that some of the online click-thru "contracts" have been making 
attempt to address this area; rather than simple "i agree"/"disagree" 
buttons ... they put little checkmarks at places in scrolled form .... you 
have to at least scroll thru the document and click on one or more 
checkmarks .... before doing the "i agree" button. a digital signature has 
somewhat higher integrity than simple clicking on the "i agree" button ... 
but wouldn't subsume the efforts to demonstrate that a person was required 
to make some effort to view document. Of course in various attack scenarios 
... simple checkmark clicks could be forged. However, the issue being 
addressed isn't a forging attack ... it is person repudiating that they 
read the T&Cs before hitting the "I agree" button.

With the depreciating of the "non-repudiation" bits in a long ago, and far 
away manufactured certificates (which has possibly absolutely no relevance 
to the conditions under which digital signatures are actually performed) 
.... there has been some evolution of "non-repudiation" processes. An issue 
for the "non-repudiation" processes is whether or not the person actually 
paid attention to what they were "signing" (regardless of the reason).

An issue for relying parties is not only was whether or not there was some 
non-repudiation process in effect, but also does the relying party have any 
proof regarding a non-repudiation process. If there is some risk and/or 
expense associated with repudiation might occur (regardless of whether or 
not it is a fraud issue), then a relying party might adjust the factors 
they use for performing some operation (i.e. they might not care as much if 
it is a low-value withdrawal transaction for $20 than if it was a 
withdrawal transaction for $1m).

some physical contracts are now adding requirement that addition to signing 
(the last page), that people are also required to initial significant 
paragraphs at various places in the contract.

--
Anne & Lynn Wheeler    http://www.garlic.com/~lynn/ 

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