# tls

## Name

*tls* - allows you to configure the server certificates for the TLS, gRPC, DoH servers.

## Description

CoreDNS supports queries that are encrypted using TLS (DNS over Transport Layer Security, RFC 7858)
or are using gRPC (https://grpc.io/ , not an IETF standard). Normally DNS traffic isn't encrypted at
all (DNSSEC only signs resource records).

The *tls* "plugin" allows you to configure the cryptographic keys that are needed for both
DNS-over-TLS and DNS-over-gRPC. If the *tls* plugin is omitted, then no encryption takes place.

The gRPC protobuffer is defined in `pb/dns.proto`. It defines the proto as a simple wrapper for the
wire data of a DNS message.

## Syntax

~~~ txt
tls CERT KEY [CA]
~~~

Parameter CA is optional. If not set, system CAs can be used to verify the client certificate

~~~ txt
tls CERT KEY [CA] {
    client_auth nocert|request|require|verify_if_given|require_and_verify
    keylog FILE
}
~~~

If client\_auth option is specified, it controls the client authentication policy.
The option value corresponds to the [ClientAuthType values of the Go tls package](https://golang.org/pkg/crypto/tls/#ClientAuthType): NoClientCert, RequestClientCert, RequireAnyClientCert, VerifyClientCertIfGiven, and RequireAndVerifyClientCert, respectively.
The default is "nocert".  Note that it makes no sense to specify parameter CA unless this option is
set to verify\_if\_given or require\_and\_verify.

The keylog can be specified to export TLS master secrets in key log format to allow external programs
to decrypt TLS connections. It compromises security and should only be used for debugging!

CoreDNS sets the minimum TLS version to TLS 1.2. The maximum TLS version, TLS 1.2 cipher suites, and
key exchange mechanisms use the Go `crypto/tls` defaults.

## Examples

Start a DNS-over-TLS server that picks up incoming DNS-over-TLS queries on port 5553 and uses the
nameservers defined in `/etc/resolv.conf` to resolve the query. This proxy path uses plain old DNS.

~~~
tls://.:5553 {
	tls cert.pem key.pem ca.pem
	forward . /etc/resolv.conf
}
~~~

Start a DNS-over-gRPC server that is similar to the previous example, but using DNS-over-gRPC for
incoming queries.

~~~
grpc://. {
	tls cert.pem key.pem ca.pem
	forward . /etc/resolv.conf
}
~~~

Start a DoH server on port 443 that is similar to the previous example, but using DoH for incoming queries.
~~~
https://. {
	tls cert.pem key.pem ca.pem
	forward . /etc/resolv.conf
}
~~~

Only Knot DNS' `kdig` supports DNS-over-TLS queries, no command line client supports gRPC making
debugging these transports harder than it should be.

## See Also

RFC 7858 and https://grpc.io.
