Posted by Matthew Mauer and Mike Yu, Android team
To help keep Android users’ DNS queries private, Android supports encrypted DNS. In addition to existing support for DNS-over-TLS, Android now supports DNS-over-HTTP/3 which has a number of improvements over DNS-over-TLS.
Most network connections begin with a DNS lookup. While transport security may be applied to the connection itself, that DNS lookup has traditionally not been private by default: the base DNS protocol is raw UDP with no encryption. While the internet has migrated to TLS over time, DNS has a bootstrapping problem. Certificate verification relies on the domain of the other party, which requires either DNS itself, or moves the problem to DHCP (which may be maliciously controlled). This issue is mitigated by central resolvers like Google, Cloudflare, OpenDNS and Quad9, which allow devices to configure a single DNS resolver locally for every network, overriding what is offered through DHCP.
In Android 9.0, we announced the Private DNS feature, which uses DNS-over-TLS (DoT) to protect DNS queries when enabled and supported by the server. Unfortunately, DoT incurs overhead for every DNS request. An alternative encrypted DNS protocol, DNS-over-HTTPS (DoH), is rapidly gaining traction within the industry as DoH has already been deployed by most public DNS operators, including the Cloudflare Resolver and Google Public DNS. While using HTTPS alone will not reduce the overhead significantly, HTTP/3 uses QUIC, a transport that efficiently multiplexes multiple streams over UDP using a single TLS session with session resumption. All of these features are crucial to efficient operation on mobile devices.
DNS-over-HTTP/3 (DoH3) support was released as part of a Google Play system update, so by the time you’re reading this, Android devices from Android 11 onwards1[…]
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