Re: Why are mail servers not also key servers?

[Yoav Nir <[e-mail]>]

On 20 Apr 2017, at 16:20, Jon <[e-mail]> wrote:

> Hi All,
> 
> I'm not sure if this is a topic which has already come up or not (I did
> a simple search brought nothing up).
> 
> Anyway, the state of email security is still pretty poor despite much
> low hanging fruit. PGP is great for those that use
> it, but they are a small group. TLS seems to be the only wide spread
> security implementation and I suspect that it has worked because it's
> transparent to the end users. So, why hasn't key exchange been made to
> be transparent? Why are (E)SMTP servers not also key servers? Have users
> generate a key pair on registration, store those keys on the server (in
> an encrypted archive), and make the public key available. A little
> coding later and we've got key exchange and message confidentiality.
> 
> Some extra security can be had by giving mail servers their own keys
> with which they can sign exchanges (and remember each other). TLS can be
> used to as part of an initial key exchange if that is desired. Can
> we not extend smtp again to include the necessary key exchange commands?
> Is there any movement on this?
> 

Hi, Jon

I’m sure such things have been considered in the past, and for certain SMTP could be extended. I can think of a few complications right of the top of my head. There are undoubtedly others:

1. People use multiple MUAs. For this account I use this Mac MUA, a phone MUA, and occasionally the web-based MUA. I’d need to share the private key to receive encrypted mail on all three. Doing it in the browser is a hard problem.

2. There’s the administrative problem of tying the SMTP server to whatever server is serving the public keys. HTTPS from the same IP address? New special DNS SRV record somehow tied to the gmail.com <http://gmail.com/> MX record?

3. How much to you trust your email provider? Because they could trivially serve the wrong public key and intercept your traffic.

Yoav