Hi Thomas,
FYI there is a company called Netki is also working on a kind of DNSSEC integration with BIP70, there's a thread here about their efforts:
If you would like to work on this, perhaps it's worth teaming up with them? Obviously they plan to have an open spec and open source implementation.
Now w.r.t. the other things - I think we have discussed this before, but to reiterate: the biggest flaw with doing things the way you suggest is that in practice, no email provider is going to implement your scheme any time soon. Most obviously the big web mail providers won't. Therefore hardly anyone will use it.
Whilst having an extension cannot really hurt, obviously, BIP70 will not be amended to reduce the certificate types it allows in favour of a system that has a very low chance of mainstream adoption. Restricting options like that would just make no sense at all.
I think your primary concern is that if your email account is hacked, someone could get a cert issued in your name, and you'd be unable to revoke it? But that's not quite true. Every CA I know of allows you to revoke a certificate that was issued for your email address if you have access to that email address. Now, if you don't know that this issuance took place, you cannot invoke that procedure of course .... but that's what certificate transparency is already working on solving in a scalable manner:
That site doesn't currently index email address certs, but it certainly could with minimal extra effort by the creators as they're almost identical to domain name certs.
So the existing infrastructure seems to have everything in place to solve that issue.
Now, if you still want a mechanism that eliminates the CA entirely, I think there's a better approach which is backwards compatible with existing email providers. It works like this:
- User sends a public key in the subject line to a one-time collector address like <random-number>@publish-email-headers.net (who runs this service is arbitrary as they do not need to be trusted). On receiving the email, the headers are made available via https://publish-email-headers.net/<random-number> for download by the users wallet.
- The act of sending the email triggers DKIM signing of the subject line and From header, and thus, the public key and email address are bound together via the ESP's own signing key.
- The textual email headers can be run through the DKIM validation algorithm in combination with the domain key retrieved via DNS.
With this scheme, setup is largely automatic and involves the wallet asking the operating system to open a mailto: URL. The user just has to press "send" and the wallet can then sit on a long-lived HTTPS connection waiting for the headers to turn up. Once the headers are downloaded, they can be saved to disk and this becomes your "DKIM certificate" which can then be used with a new pki_type in BIP70.
Note the following useful characteristics of this approach:
- It does not require the email provider to know/care about Bitcoin. DKIM is already widely deployed by major email providers due to its benefits for spam and phishing protection: the majority of all email on the internet is DKIM signed. So you automatically have a system that works with nearly all consumer email accounts.
- The enrolment UI is straightforward, assuming the user has a working mailto: handler on their system. Even webmail services like Gmail can attach themselves to mailto: handling these days.
- There are DKIM validation libraries already in existence, so new code required is minimal.
And the downsides:
- There is no way to revoke such a "certificate" because you have, of course, abandoned the PKI which specifies how to handle all these details. You could potentially hijack/reuse OCSP to allow such a custom cert to be revoked, but then the question is, who actually runs such a revocation server. Doing things like this is why we have CAs in the first place.
- The UX leaves a bit of binary nonsense in the users sent folder that clutters up their account.
- Does it even solve the right problem? A lot of users don't actually use emails as identifiers anymore. In the modern world people are using their social networking profiles (i.e. Facebook) and phone numbers (e.g. for WhatsApp) as the personal identifier of choice. Email address support might be solving yesterdays problem.