On Wed, Jan 07, 2015 at 02:07:25PM -0600, John Hascall wrote:
> Assume I have a domain with DNSSEC and inbound mail servers behind a
> (load-balanced) MX which support TLS.
With All of the MX hosts having the same private key and certificate:
> If I've been following along correctly, if I publish a DNS record of the
> form:
>
> _25._tcp.mx.example.org. IN TLSA 3 1 1 *<sha2-256 digest of DER leaf public
> key in X.509 SPKI format>*
Or else multiple such TLSA RRs one per real MX host behind the load-balancer,
if the number of back-end hosts is reasonably small.
> this will make some (currently smallish?) set of mail servers sending to me
> have a better assurance they are really talking to me.
> Is this correct?
Yes, and definitely smallish. Basically folks running Postfix 2.11 with:
smtp_dns_support_level = dnssec
smtp_tls_security_level = dane
and a validating resolver on 127.0.0.1 as the only entry in /etc/resolv.conf
I have no count of sites that implement client-side DANE, I can
only survey the domains that publish TLSA RRs for such sites to
use.
> And does "*leaf public key" *refer to the public key associated with the
> cert used for STARTTLS or ...something else...?
The former:
printf '_25._tcp.%s. IN TLSA 3 1 1 %s\n' \
$(uname -n) \
$(openssl x509 -in cert.pem -noout -pubkey |
openssl pkey -pubin -outform DER |
openssl dgst -sha256 -binary |
hexdump -ve '/1 "%02x"')
--
Viktor.
