doh-proxy

A DNS-over-HTTP server proxy in Rust. Add a webserver and you get DNS-over-HTTPS, which is actually DNS-over-HTTP/2.

Installation

Without built-in support for HTTPS:

sh cargo install doh-proxy

With built-in support for HTTPS (requires openssl-dev):

sh cargo install doh-proxy --features=tls

Usage

```text A DNS-over-HTTP server proxy

USAGE: doh-proxy [FLAGS] [OPTIONS]

FLAGS: -K, --disable-keepalive Disable keepalive -P, --disable-post Disable POST queries -h, --help Prints help information -V, --version Prints version information

OPTIONS: -E, --err-ttl TTL for errors, in seconds [default: 2] -l, --listen-address Address to listen to [default: 127.0.0.1:3000] -b, --local-bind-address Address to connect from [default: 0.0.0.0:0] -c, --max-clients Maximum number of simultaneous clients [default: 512] -X, --max-ttl Maximum TTL, in seconds [default: 604800] -T, --min-ttl Minimum TTL, in seconds [default: 10] -p, --path URI path [default: /dns-query] -u, --server-address Address to connect to [default: 9.9.9.9:53] -t, --timeout Timeout, in seconds [default: 10] -I, --tls-cert-password Password for the PKCS12-encoded identity (only required for built-in TLS)

-i, --tls-cert-path <tls_cert_path>              Path to a PKCS12-encoded identity (only required for built-in TLS)

```

HTTP/2 termination

The recommended way to use doh-proxy is to use a TLS termination proxy (such as hitch or relayd), a CDN or a web server with proxying abilities as a front-end.

That way, the DoH service can be exposed as a virtual host, sharing the same IP addresses as existing websites.

If doh-proxy and the HTTP/2 front-end run on the same host, using the HTTP protocol to communicate between both is fine.

If both are on distinct networks, such as when using a CDN, doh-proxy can handle HTTPS requests, provided that it was compiled with the tls feature.

The identity must be encoded in PKCS12 format. Given an existing certificate cert.pem and its secret key cert.key, this can be achieved using the openssl command-line tool:

sh openssl pkcs12 -export -out cert.p12 -in cert.pem -inkey cert.key

A password will be interactive asked for, but the -passout command-line option can be added to provide it non-interactively.

Once done, check that the permissions on cert.p12 are reasonable.

In order to enable built-in HTTPS support, add the --tls-cert-path option to specify the location of the cert.p12 file, as well as the password using --tls-cert-password.

Once HTTPS is enabled, HTTP connections will not be accepted.

Operational recommendations

DoH can easily be detected and blocked using SNI inspection. As a mitigation, DoH endpoints should preferably share the same virtual host as existing, popular websites, rather than being on dedicated virtual hosts.
When using DoH, DNS stamps should include a resolver IP address in order to remove a dependency on non-encrypted, non-authenticated, easy-to-block resolvers.
Unlike DNSCrypt where users must explicitly trust a DNS server public key, the security of DoH relies on traditional public Certificate Authorities. Additional root certificates (required by governments, security software, enterprise gateways) installed on a client immediately make DoH vulnerable to MITM. In order to prevent this, DNS stamps should include the hash of the parent certificate.
TLS certificates are tied to host names. But domains expire, get reassigned and switch hands all the time. If a domain originally used for a DoH service gets a new, possibly malicious owner, clients still configured to use the service will blindly keep trusting it if the CA is the same. As a mitigation, the CA should sign an intermediate certificate (the only one present in the stamp), itself used to sign the name used by the DoH server. While commercial CAs offer this, Let's Encrypt currently doesn't.
Make sure that the front-end supports HTTP/2 and TLS 1.3.

Example usage with Nginx

In an existing server, a /doh endpoint can be exposed that way:

text location /doh { proxy_pass http://127.0.0.1:3000; }

This example assumes that the DoH proxy is listening locally to port 3000.

HTTP caching can be added (see the proxy_cache_path and proxy_cache directives in the Nginx documentation), but be aware that a DoH server will quickly create a gigantic amount of files.

Use the online DNS stamp calculator to compute the stamp for your server, and the dnscrypt-proxy -show-certs command to print the TLS certificate hashes to be added it.

Clients

doh-proxy can be used with dnscrypt-proxy as a client.

doh-proxy is currently being used by the doh.crypto.sx public DNS resolver.

An extensive list of public DoH servers can be found here: public encrypted DNS servers.