Microsoft has announced that an upcoming version of Windows 10 will have support for DNS over HTTPS (also called DoH) built into the Windows DNS client. This is a major change in how Domain Name System queries will be handled by the OS, and fits in with some evolving efforts that are going on industry-wide.
DNS over HTTPS proposals that have seen light will have the effect of preventing on-path eavesdropping, spoofing and blocking of DNS requests.
Domain Name System (DNS) is the Internet's naming protocol. It translates names like example.com into the actual numeric IP address of a destination server. Currently, this is done in plaintext which can -- for example -- be recorded by an internet service provider and ascribed to a user. Indeed, some ISPs have found the compiling of this data to be a major revenue stream for them.
But ISPs say that they are concerned that DoH use will complicate the use of captive portals, which are used to intercept connections briefly to force users to log on to a network, and will make it more difficult to block content at the resolver level.
The ISPs are also concerned that browser makers will cut them out of the future DNS action by directing DNS traffic to specific resolvers that the makers can choose. This would contribute to the centralization of Internet infrastructure, as thousands of DNS resolvers used for web requests would be replaced by a small handful. DoH advocates, like Mozilla and the EFF, have responded by suggesting the ISPs create the DoH DNS resolution servers themselves, and by including in DoH proposals a way to allow users to choose specific resolvers.
DoH will add a layer of privacy-enhancing encryption to DNS traffic, but it comes at a price. Even MSFT says, "Providing encrypted DNS support without breaking existing Windows device admin configuration won't be easy." They realize that in order to keep the DNS decentralized, it will be important for client operating systems (such as Windows) and Internet service providers alike to widely adopt encrypted DNS.
MSFT says that it is prioritizing DoH support as the most likely to provide immediate value "to everyone." DoH allows them to reuse existing HTTPS infrastructure, for example.
To make things work with less friction, MSFT says their upcoming DoH system, "will look for opportunities to encrypt Windows DNS traffic without changing the configured DNS resolvers set by users and system administrators."
They are starting by using DoH for DNS servers Windows is already configured to use. 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. And if both endpoints support encryption, they say that "there's no reason to wait around for permission to use encryption."
MSFT sees DoH (or a variant) as inevitable in the future. With this advisory, they are reassuring their customers that they will not leave them with obsolete systems.
— Larry Loeb has written for many of the last century's major "dead tree" computer magazines, having been, among other things, a consulting editor for BYTE magazine and senior editor for the launch of WebWeek.