DNSCrypt - ArchWiki

# DNSCrypt

DNSCrypt is a piece of software that encrypts DNS traffic between the user and a DNS resolver, preventing spying, spoofing or man-in-the-middle attacks.

## Installation

Install dnscrypt-proxy from the official repositories.

## Configuration

Tip: To automatically configure DNSCrypt and choose a resolver, use dnscrypt-autoinstall from the AUR.

By default dnscrypt-proxy is pre-configured in `/etc/conf.d/dnscrypt-proxy` (read by `dnscrypt-proxy.service`) to accept incoming requests on `127.0.0.1` to an OpenDNS resolver. See the list of public resolvers for alternatives.

With this setup, it will be necessary to alter your resolv.conf file and replace your current set of resolver addresses with localhost:

    nameserver 127.0.0.1

You might need to prevent other programs from overwriting it, see resolv.conf#Preserve DNS settings for details.

## Starting

Available as a systemd service: `dnscrypt-proxy.service`

## Tips and tricks

### DNSCrypt as a forwarder for local DNS cache

It is recommended to run DNSCrypt as a forwarder for a local DNS cache, otherwise every single query will make a round-trip to the upstream resolver. Any local DNS caching program should work, examples below show configuration for Unbound, dnsmasq, and pdnsd.

#### Example: configuration for Unbound

Configure Unbound to your liking (remember to set /etc/resolv.conf to use the local DNS server) and add the following lines to the end of the `server` section in `/etc/unbound/unbound.conf`:

    do-not-query-localhost: no
    forward-zone:
      name: "."
      forward-addr: 127.0.0.1@40

Note: Port 40 is given as an example as Unbound by default listens to 53, these must be different.

Start the systemd service `unbound.service`. Then configure DNScrypt to match Unbound's new `forward-zone` IP and port in `/etc/conf.d/dnscrypt-proxy`:

    DNSCRYPT_LOCALIP=127.0.0.1
    DNSCRYPT_LOCALPORT=40

Note: DNSCrypt needs to start before Unbound, so include `unbound.service` on a `Before=` line in the `[Unit]` section of `dnscrypt-proxy.service`.

Restart `dnscrypt-proxy.service` and `unbound.service` to apply the changes.

#### Example: configuration for dnsmasq

Configure dnsmasq as a local DNS cache. The basic configuration to work with DNSCrypt:

    /etc/dnsmasq.conf

    no-resolv
    server=127.0.0.2#2053
    listen-address=127.0.0.1

If you configured DNSCrypt to use a resolver with enabled DNSSEC validation, make sure to enable it also in dnsmasq:

    /etc/dnsmasq.conf

    proxy-dnssec

Configure DNSCrypt to listen on `127.0.0.2`, where dnsmasq will be querying:

    /etc/conf.d/dnscrypt-proxy

    DNSCRYPT_LOCALIP=127.0.0.2
    DNSCRYPT_LOCALPORT=2053

Restart `dnscrypt-proxy.service` and `dnsmasq.service` to apply the changes.

#### Example: configuration for pdnsd

Install pdnsd. A basic configuration to work with DNSCrypt is:

    /etc/pdnsd.conf

    global {
    	perm_cache=16384;
    	cache_dir="/var/cache/pdnsd";
    	run_as="pdnsd";
     	server_ip = 127.0.0.1;
    	status_ctl = on;
    	query_method=udp_tcp;
    	min_ttl=15m;       # Retain cached entries at least 15 minutes.
    	max_ttl=1w;        # One week.
    	timeout=10;        # Global timeout option (10 seconds).
    	neg_domain_pol=on;
    	udpbufsize=1024;   # Upper limit on the size of UDP messages.
    }

    server {
    	label = "dnscrypt-proxy";
    	ip = 127.0.0.2;
    	port = 53;
    	timeout = 4;
    	uptest = query;
    	interval = 15m;
    	proxy_only=on;
    }

    source {
    	owner=localhost;
    	file="/etc/hosts";
    }

    rr {
    	name=localhost;
    	reverse=on;
    	a=127.0.0.1;
    	owner=localhost;
    	soa=localhost,root.localhost,42,86400,900,86400,86400;
    }

Configure DNSCrypt to listen on `127.0.0.2:53` where pdnsd will be querying. The following has an example provider already in place. Be sure to use the provider you have chosen.

    /etc/conf.d/dnscrypt-proxy

    DNSCRYPT_LOCALIP=127.0.0.2
    DNSCRYPT_LOCALPORT=53
    DNSCRYPT_USER=nobody
    DNSCRYPT_PROVIDER_NAME=2.dnscrypt-cert.opendns.com
    DNSCRYPT_PROVIDER_KEY=B735:1140:206F:225D:3E2B:D822:D7FD:691E:A1C3:3CC8:D666:8D0C:BE04:BFAB:CA43:FB79
    DNSCRYPT_RESOLVERIP=208.67.220.220
    DNSCRYPT_RESOLVERPORT=443

Be sure you have configured resolv.conf properly for `127.0.0.1`.

Uncomment the following line in `pdnsd.service`:

`Before=pdnsd.service`

Now enable both the `pdnsd` and `dnscrypt-proxy` services.

### Enable EDNS0

Extension Mechanisms for DNS that, among other things, allows a client to specify how large a reply over UDP can be.

Add the following line to your `/etc/resolv.conf`:

    options edns0

You may also wish to add the following argument to dnscrypt-proxy:

    --edns-payload-size=<bytes>

The default size being 1252 bytes, with values up to 4096 bytes being purportedly safe. A value below or equal to 512 bytes will disable this mechanism, unless a client sends a packet with an OPT section providing a payload size.

#### Test EDNS0

Make use of the DNS Reply Size Test Server, use the dig command line tool available with dnsutils from the official repositories to issue a TXT query for the name rs.dns-oarc.net:

    $ dig +short rs.dns-oarc.net txt

With EDNS0 supported, the output should look similar to this:

    rst.x3827.rs.dns-oarc.net.
    rst.x4049.x3827.rs.dns-oarc.net.
    rst.x4055.x4049.x3827.rs.dns-oarc.net.
    "2a00:d880:3:1::a6c1:2e89 DNS reply size limit is at least 4055 bytes"
    "2a00:d880:3:1::a6c1:2e89 sent EDNS buffer size 4096"

Categories:

- Domain Name System
- Security