Proposal of OpenPGP Email Validation

MFPA 2014-667rhzu3dc-lists-groups at
Tue Jul 28 19:26:07 CEST 2015

Hash: SHA512


On Monday 27 July 2015 at 6:55:24 PM, in
<mid:55B6708C.9090007 at>, nico at wrote:

> If the
> goal is to keep validations in sync,   key owners might
> have to confirm emails added over the year   earlier,
> which shouldn't be too bad. - - If the goal is to
> reduce validation requests, I see no   problem to have
> different expiration dates. I think, because each email
> should be validated from time to time anyway (and this
> is an isolated process), each validation should give
> the 12 month period for the specific email when it is
> validated. Or do you see any problems?

I just think if I was to receive revalidation requests all at the same
time I would be less likely to overlook those for little-used email
addresses I do not often check. It also keeps it neat.

> This whole approach is NOT to make a perfect prove that
> the email is correct.

Nothing is perfect. Even meeting up and verifying government-issued ID
documents can be defeated by good quality fake documents.

> It only says that the email did
> one day work for a validation of any kind, which is
> more than what we have now.

We have the Web of Trust to demonstrate that. But those are generally
one-off signatures on a key, and may be quite a few years old. Some
email providers recycle addresses, so an address Bob used a few months
or years ago could now be under Alice's, or even Mallory's, control.

As far as I see it, your scheme adds two things: periodic
revalidation, and an easy way to get a signature on your key without
having to meet anybody.

> That is, such a validation
> does not give full trust, it would only give slightly
> more trust over emails that do not have the validation.

Indeed. I think an annual revalidation period strikes a reasonable
balance, although maybe there are email services that recycle
addresses more quickly than that.

> But that might be enough to solve the faked key issue.

Are there really many "faked" keys, rather than keys that are no
longer used, forgotten passphrase, lost private key, etc.?

> this solution does NOT solve the
> problem of interception of emails. But it helps to
> detect them

How does this help to detect interception of emails?

> It depends on whether and how far you trust the
> provider. Reality looks different (see startmail,
> posteo, riseup, and many company email servers). I
> don't claim to solve any problem in that area.
> User/clients might have to decide whether to trust a
> validation notation given by posteo, riseup, google,
> ...

Company email servers, I would expect companies as a matter of course
to have a means to decrypt their employees' emails.

I'm shocked to read [0] that Riseup once had a webmail option that
stored the user's public and private keys. Riseup now tells [1] users
who want to use encrypted email to utilize an email client to send and
receive email, while keeping their private key stored safely on their
local machine.

[0] <>
[1] <>

Startmail sounds like a similar concept to Hushmail, which was
compromised by a court order obtained through a mutual assistance
treaty. It is not clear to me why Startmail would not be expected to
suffer the same fate.

Posteo looks interesting. But their overview says end-to-end
encryption is done by the user in addition to Posteo's own security
measures, so the user would have to generate and store their own keys.

And Google make a living out of exploiting data mined from users'
emails and search activities. Why would anybody trust them?

>> In your proposal for listing validation signatures in
>> GnuPG: "‘!’ after sig signals successful validation" -
>> why is this needed? Surely the mere presence of a
>> validation signature signals successful validation.

> Hmm, Wener recommended to use  --check-sigs rather than
> --list.sigs which then results in printing the '!'.
> Isn't it necessary in your opinion?

Fair enough. The mere presence of a validation signature from the
validation server indicates successful validation of the email address
in the UID. The "!" after "sig" in the output of --check-sigs
indicates the signature has been checked and found to be "good" or

- --
Best regards

MFPA                  <mailto:2014-667rhzu3dc-lists-groups at>

A woman's mind is cleaner than a man's: She changes it more often.


More information about the Gnupg-users mailing list