Re: Shell's authentication needs

At 4:36 PM 01/24/95, L. McCarthy wrote:
>Rich Salz writes:
>> Shell needs public key because they want to use email for legal contracts.
>> They've been waiting for standards to come around, but have given up.
>> They're currently planning on using NIST's DSS, if they can fix a few things:
>>     - Add concepts of time and location (it can be important to prove
>>       that this was signed last month outside of the U.S.)
>
>Any thoughts on how digital "place-stamping" (analogous to timestamping) might
>be accomplished, to authenticate the location of origin of a document ?

Well, it clearly can't be done over the internet.   But it's really just a
matter of putting a "place" field within the signature, in addition to the
"time" one.   And you'd have to trust the "stamper" to only stamp stuff as
"Cleveland" that he had a way of knowing was in Cleveland. It's really up
to him to figure out a way of verifying that. Maybe American Express
offices will start place/time stamping, and you have to physically go to
the AE office in Cleveland OH where someone takes your file and place/time
stamps it.
It's not as elegant as time stamping, because you really need face-to-face
contact. And you need to trust the stamper not to lie about his location (I
can't remember how much you need to trust a time-stamper, but I think it's
less).

On Tue, 24 Jan 1995, Jonathan Rochkind wrote:
> It's not as elegant as time stamping, because you really need face-to-face
> contact. And you need to trust the stamper not to lie about his location (I
> can't remember how much you need to trust a time-stamper, but I think it's
> less).

You do not need to trust the time stamper at all, because from time
to time he publishes a one way checksum of everything he has
time stamped, or rather the audit trail for everything he
has time stamped.

So if the credibility of his stamp is questioned he just produces
the audit trail, and you know that the audit trail must have 
been created at the time claimed, because its checksum was
published at the time claimed.


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