Stop Using Encrypted Email

Re:Stop Using Encrypted Email by alwillis on Thursday February 20, 2020 @07:10AM (#22374476)

DANE is only an option if your zone is DNSSEC signed and you have control of your DNS. Of course, there are other ways you can go: https://slxh.nl/blog/2016/pgp-and-dns/

You’re in control of publishing your public key, not the email provider.

I’d be remiss if I didn’t tell you how bad MTA-STS is:

* MTA-STS: compromise for the DNSSEC-challenged

    * Still can and should prefer DANE outbound

    * Authenticates domain control via CA leap of faith

    * Vulnerable to MiTM at cert bootstrap

    * Vulnerable to weakest root CA, and unauthorized certs

    * Open to downgrade on first (or irregular) contact

    * Complex mix of HTTPS, unsigned DNS and SMTP

[ Parent | on HN ]

Re:Stop Using Encrypted Email by jcranmer on Thursday February 20, 2020 @09:23AM (#22375229)

> You’re in control of publishing your public key, not the email provider.

This is only true if you personally fully own the domain and have control of the DNS and other services, which is not the case for the utter majority (at least 99.9%, maybe a few more 9s) of the population. Of course, in that case, you are pretty much the email provider, so not trusting the email provider is a pretty questionable scenario at that point.

> MTA-STS: compromise for the DNSSEC-challenged

Yeah... DNSSEC is a classic example of a solution looking for a problem. Most of your criticism would apply equally well to not using DANE for TLS, and every browser vendor has looked at it and decided against it because it adds no security.

[ Parent | on HN ]

Re:Stop Using Encrypted Email by alwillis on Thursday February 20, 2020 @11:16AM (#22376110)

Having cryptographically signed DNS records that can’t be forged and can be validated is good thing, which is what DNSSEC provides.

Right now, DANE is the only way to mitigate downgrade attacks with SMTP and TLS connections. Apparently use of DANE for email is growing [1].

DANE hasn’t taken off with browser vendors because of their concern about additional DNS lookups when making TLS connections.

[1]: “Number of DANE-enabled mail domains growing exponentially”—https://www.sidn.nl/en/news-and-blogs/number-of-dane-enabled...

[ Parent | on HN ]

Re:Stop Using Encrypted Email by tptacek on Thursday February 20, 2020 @11:28AM (#22376199)

If that were the case, browser vendors would have helped push the DNSSEC chain-extensions forward, which were designed exactly to avoid doing DNS lookups to carry DANE records. Instead, the browser vendors laughed at the chain-extensions effort, and it died in committee.

[ Parent | on HN ]

Re:Stop Using Encrypted Email by alwillis on Thursday February 20, 2020 @12:37PM (#22376813)

Just pointing out that MTA-STS doesn’t mitigate downgrade attacks and that DNSSEC/DANE does: https://www.rfc-editor.org/rfc/rfc7672.html#section-1.3.1

And right from the MTA-STS RFC: https://www.rfc-editor.org/rfc/rfc8461.html#section-2

the mechanism described here instead relies on certification authorities (CAs) and does not require DNSSEC, at a cost of risking malicious downgrades.

So there’s that.

[ Parent | on HN ]