John Levine wrote:
If the cert has not been revoked (by checking), then you know that
the person that used the cert had permission to use that 'From' address.
Well, not quite, you know that the CA that signed the cert thought
that the sender had permission to use that address.
Which is why I said:
"The signature only means - yes the signature matches the From line. "
and
"*IF* you trust the CA in the signature, then you trust that it came from
a valid user of that email address and was not forged. "
*IF* you trust the CA in the signature, then you trust that it came from
a valid user of that email address and was not forged.
We're back to the key management problem. I don't see how a public
signer that signed enough keys to be useful as a whitelist wouldn't
also let enough bad guys sneak through that you'd want to use it as
a blacklist.
I do not know of anyone selling keys for a white or black list. I do
know of a few
CAs that sell certs that match the domains they check them against. The CA
sell certs that match the 'From' line, they do not declare the email
address pure.
For small and reasonably well defined communities, a company signing
its employees certs, or various geekly groups who know each other,
sigs can work, but I've never been able to see a plausible way to
scale up to the whole world of e-mail.
This is mixing subjects. Being able to validate that the 'From' line is
not forged
has nothing to do with black or white lists. You can black or white list
based on email address as well as certs - no change to scaleability.
If over time I learn that 'spam-certs-ca' sells certs for any domain name
I can blacklist any cert signed by them. MUCH more scalable that
trying to guess the thousands 'From' address that may be sending spam.
--
Doug Royer | http://INET-Consulting.com
-------------------------------|-----------------------------
Doug(_at_)Royer(_dot_)com | Office: (208)520-4044
http://Royer.com/People/Doug | Fax: (866)594-8574
| Cell: (208)520-4044
We Do Standards - You Need Standards
smime.p7s
Description: S/MIME Cryptographic Signature