If you connect to a website using a “secure” connection over TLS/SSL, how do you know you are using the correct TLS/SSL certificate?
You may see the “lock” icon in your web browser, but are you sure that you are connecting all the way to the website using the correct TLS certificate? It is in fact quite possible – and quite common – for a firewall or other device in your network path to terminate your TLS connection with a website and then re-create a TLS connection from the device to your browser. You think you have a secure, encrypted connection to your bank, for instance, but in fact your connection has been intercepted and the firewall or other device is able to see, and potentially record, all your interaction with the web site.
With DNSSEC now being deployed, a new protocol has emerged called “DANE” (“DNS-Based Authentication of Named Entities“) that allows you to securely specify exactly which TLS/SSL certificate an application or service should use to connect to your site. If, for instance, a web browser supporting DANE detects that it is NOT using the specified certificate, it can warn you that your connection is insecure… even though you see a “lock” icon. Beyond the web, DANE is being used with great success in securing communication over email and over instant messaging protocols such as XMPP (Jabber). There is also interest in using DANE for SIP (voice-over-IP (VoIP)) and other communication methods.
DANE is defined in RFC 6698 and over time we will be adding more tutorials and document to this site to help you understand both how DANE helps make the Internet more secure and also how you can get started either publishing TLSA records for your domain – or using DANE within your application.
It is important to note that the DANE protocol can work perfectly fine with existing TLS certificates issued by Certificate Authorities (CAs). DANE defines four different modes of operation in the “certificate usage” field of a TLSA record:
- 0 – CA specification – The TLSA record specifies the Certificate Authority (CA) who will provide TLS certificates for the domain. Essentially, you are able to say that your domain will ONLY use TLS certificates from a specific CA. If the browser or other application using DANE validation sees a TLS cert from another CA the app should reject that TLS cert as bogus.
- 1 – Specific TLS certificate – The TLSA record specifies the exact TLS certificate that should be used for the domain. Note that this TLS certificate must be one that is issued by a valid CA.
- 2 – Trust anchor assertion – The TLSA record specifies the “trust anchor” to be used for validating the TLS certificates for the domain. For example, if a company operated its own CA that was not in the list of CAs typically installed in client applications this usage of DANE could supply the certificate (or fingerprint) for their CA.
- 3 – Domain-issued certificate – The TLS record specifies the exact TLS certificate that should be used for the domain, BUT, in contrast to usage #1, the TLS certificate does not need to be signed by a valid CA. This allows for the use of self-signed certificates.
The flexibility of the different usage modes of the DANE protocol means that it can be used to provide a DNSSEC-validated additional layer of trust for regular CA-signed TLS certificates – and it can also be used to add a DNSSEC-validated layer of trust to self-signed certificates.
A good introduction to DANE is an IETF Journal article published in October 2011 titled “DANE: Taking TLS Authentication to the Next Level Using DNSSEC“. In the article, Richard Barnes explains why DANE is needed, outlines how it works, digs into some of the challenges with DANE implementation and provides a good number of links for more information.
Content Providers
If you would like to create a TLSA record for your site, several tools are available to help:
Application Developers
The following libraries are in the process of adding support for the DANE protocol:
- dnspython – the development version of dnspython found on Github has had support for TLSA records added to the code base. This is not yet available in a formal release.
- ldns – an upcoming release of ldns will provide support for DANE (this page will be updated when the release occurs).
Other resources for developers:
- DANE Test Sites – If you are adding DANE support to your application and wish to test out how well it works, the sites on this page are early supporters of the protocol and can be used in your testing.
Getting More Involved
If you would like to get more involved in the development of the DANE protocol and supporting documentation, you can:
- Read the RFCs and other documents associated with DANE
- Understand the DANE working group charter
- Join the DANE mailing list