Technical challenge, or am I missing something...

[vlape at me.com (Vincent Lape)]

For electronic sigs i use USPS EPM (US Post Office Electronic  
Postmark). Its pretty easy to configure and is not all that expensive.  
You do have to pay per sig (kinda like buying a stamp) however you can  
see a history of the "signatures" purchased. You can get over the  
whole "he faked the date" thing because the signature includes date  
and time the signature was applied.

take a peek at http://www.usps.com/electronicpostmark/welcome.htm and 
http://office.microsoft.com/en-us/help/HA010971711033.aspx

Hope this helps
On Oct 13, 2009, at 11:37 AM, Soft Reset wrote:

> Ok, something to (hopefully) challenge you with:
>
> I often send email digitally signed so that receivers can not modify  
> the message and claim I wrote it (the modified version).  However,  
> if I do that, what is stopping the receiver from claiming "they  
> never got it" and I'm falsifying the email in the first place?  If I  
> include the date in the signed message, they can still claim I put  
> *any* date I wanted in there.
>
> For clarity, consider this scenario:
>
> Dan writes and signs the following message and sends it to Tracy on  
> Jan 1, 2009:
>
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> Hello Tracy, today is January 1, 2009
> -----BEGIN PGP SIGNATURE-----
> Version: GnuPG v1.4.9 (GNU/Linux)
>
> iEYEARECAAYFAkoOqzMACgkQ3GktKdDXU7up4QCglGa6gjD8MX3Gytushc65cVkA
> IJkAniZ3hQ1WyC0SbecPJRKY9xeSsHTA
> =KqXV
> -----END PGP SIGNATURE-----
>
> Dan then tells the boss, "I sent the email to Tracy."
>
> Tracy claims, "I never got any such email.  He probably just made  
> the email, faked the date and then signed it to make it look legit.   
> He's lying!"
>
>
> ====================
>
> Assuming the mail server administrators have no sense of logging or  
> auditing, what can Dan do to provide "proof" of sending?
>
> Thanks again everyone!
>
> --SR6
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