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Smack/documentation/dnssec.md
Florian Schmaus a1630d033e Add support for DNSSEC/DANE 
This closes the cycle which started with a GSOC 2015 project under the
umbrella of the XSF adding DNSSEC/DANE support to MiniDNS.

Fixes SMACK-366.
2016-10-31 10:45:38 +01:00

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DNSSEC and DANE

Back

DNSSEC and DANE support in Smack and MiniDNS is still in its infancy. It should be considered experimental and not ready for production use at this time. We would like to see more thorough testing and review by the security community. If you can help, then please do not hesitate to contact us.

About

DNSSEC (RFC 4033 and others) authenticates DNS answers, positive and negative ones. This means that if a DNS response secured by DNSSEC turns out to be authentic, then you can be sure that the domain either exists, and that the returned resource records (RRs) are the ones the domain owner authorized, or that the domain does not exists and that nobody tried to fake its non existence.

The tricky part is that an application using DNSSEC can not determine whether a domain uses DNSSEC, does not use DNSSEC or if someone downgraded your DNS query using DNSSEC to a response without DNSSEC.

DANE allows the verification of a TLS certificate with information stored in the DNS system and secured by DNSSEC. Thus DANE requires DNSSEC.

Prerequisites

From the three DNS resolver providers (MiniDNS, javax, dnsjava) supported by Smack only MiniDNS currently supports DNSSEC. MiniDNS is the default resolver when smack-android is used. For other configurations, make sure to add smack-resolver-minidns to your dependencies and call MiniDnsResolver.setup() prior using Smack (e.g. in a static {} code block).

DNSSEC API

Smack's DNSSEC API is very simple: Just use ConnectionConfiguration.Builder..setDnssecMode(DnssecMode) to enable DNSSEC. DnssecMode can be one of

  • disabled
  • needsDnssec
  • needsDnssecAndDane

The default is disabled.

If needsDnssec is used, then Smack will only connect if the DNS results required to determine a host for the XMPP domain could be verified using DNSSEC.

If needsDnssecAndDane then DANE will be used to verify the XMPP service's TLS certificate if STARTTLS is used. Note that you may want to configure ConnectionConfiguration.Builder.setSecurityMode(SecurityMode.required) if you use this DNSSEC mode setting.

Best practices

We recommend that applications using Smack's DNSSEC API do not ask the user if DNSSEC is avaialble. Instead they should check for DNSSEC suport on every connection attempt. Once DNSSEC support has been discovered, the application should use the needsDnssec mode for all future connection attempts. The same scheme can be applied when using DANE. This approach is similar to the scheme established by to "HTTP Strict Transport Security" (HSTS, RFC 6797).