DNS-over-HTTPS is a relatively young web protocol, implement about two years ago. It is intended to increase user privacy and security by preventing eavesdropping and manipulation of DNS data by man-in-the-middle attacks by using the HTTPS protocol to encrypt the data between the DoH client and the DoH-based DNS resolver.
The Windows Core Networking team are being busy with adding the DoH support to the OS. Here are their guiding principles on making decisions what kind of DNS encryption Windows will support and how it will be configured.
- Windows DNS needs to be as private and functional as possible by default without the need for user or admin configuration because Windows DNS traffic represents a snapshot of the user’s browsing history. To Windows users, this means their experience will be made as private as possible by Windows out of the box. For Microsoft, this means we will look for opportunities to encrypt Windows DNS traffic without changing the configured DNS resolvers set by users and system administrators.
- Privacy-minded Windows users and administrators need to be guided to DNS settings even if they don't know what DNS is yet. Many users are interested in controlling their privacy and go looking for privacy-centric settings such as app permissions to camera and location but may not be aware of or know about DNS settings or understand why they matter and may not look for them in the device settings.
- Windows users and administrators need to be able to improve their DNS configuration with as few simple actions as possible. We must ensure we don't require specialized knowledge or effort on the part of Windows users to benefit from encrypted DNS. Enterprise policies and UI actions alike should be something you only have to do once rather than need to maintain.
- Windows users and administrators need to explicitly allow fallback from encrypted DNS once configured. Once Windows has been configured to use encrypted DNS, if it gets no other instructions from Windows users or administrators, it should assume falling back to unencrypted DNS is forbidden.
Based on these principles, the team are making plans to adopt DNS over HTTPS (or DoH) in the Windows DNS client. As a platform, Windows Core Networking seeks to enable users to use whatever protocols they need, so we’re open to having other options such as DNS over TLS (DoT) in the future. As of now, they are working to support DoH because it will allow them to reuse their existing HTTPS infrastructure.
For the first milestone, they gonna use DoH for DNS servers Windows is already configured to use. There are now several public DNS servers that support DoH, and if a Windows user or device admin configures one of them today, Windows will just use classic DNS (without encryption) to that server. However, since these servers and their DoH configurations are well known, Windows can automatically upgrade to DoH while using the same server. The team claims the following benefits from this change:
- We will not be making any changes to which DNS server Windows was configured to use by the user or network. Today, users and admins decide what DNS server to use by picking the network they join or specifying the server directly; this milestone won’t change anything about that. Many people use ISP or public DNS content filtering to do things like block offensive websites. Silently changing the DNS servers trusted to do Windows resolutions could inadvertently bypass these controls and frustrate our users. We believe device administrators have the right to control where their DNS traffic goes.
- Many users and applications that want privacy will start getting the benefits without having to know about DNS. In line with principle 1, the DNS queries become more private with no action from either apps or users. When both endpoints support encryption, there’s no reason to wait around for permission to use encryption!
- We can start seeing the challenges in enforcing the line on preferring resolution failure to unencrypted fallback. In line with principle 4, this DoH use will be enforced so that a server confirmed by Windows to support DoH will not be consulted via classic DNS. If this preference for privacy over functionality causes any disruption in common web scenarios, we’ll find out early.
In the future, Windows 10 will include the ability to configure DoH servers explicitly.