Difference between revisions of "DNSCrypt"

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(example of how to test DNS server response size re: EDNS0)
(Brief walkthrough on combining DNScrypt with Unbound)
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[[en:DNScrypt]]
 
[[en:DNScrypt]]
 
[https://github.com/opendns/dnscrypt-proxy 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.
 
[https://github.com/opendns/dnscrypt-proxy 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 ==
 
== Installation ==
 
Install {{Pkg|dnscrypt-proxy}} from the [[official repositories]].
 
Install {{Pkg|dnscrypt-proxy}} from the [[official repositories]].
 
 
== Configuration ==
 
== Configuration ==
 
By default ''dnscrypt-proxy'' is pre-configured in {{ic|/etc/conf.d/dnscrypt-proxy}} to accept incoming requests on {{ic|127.0.0.1}} to an [https://opendns.com OpenDNS] resolver:
 
By default ''dnscrypt-proxy'' is pre-configured in {{ic|/etc/conf.d/dnscrypt-proxy}} to accept incoming requests on {{ic|127.0.0.1}} to an [https://opendns.com OpenDNS] resolver:
 
 
  DNSCRYPT_LOCALIP=127.0.0.1
 
  DNSCRYPT_LOCALIP=127.0.0.1
 
  DNSCRYPT_LOCALPORT=53
 
  DNSCRYPT_LOCALPORT=53
Line 17: Line 14:
 
  DNSCRYPT_RESOLVERIP=208.67.220.220
 
  DNSCRYPT_RESOLVERIP=208.67.220.220
 
  DNSCRYPT_RESOLVERPORT=443
 
  DNSCRYPT_RESOLVERPORT=443
 
 
The above file is read by {{ic|/usr/lib/systemd/system/dnscrypt-proxy.service}}:
 
The above file is read by {{ic|/usr/lib/systemd/system/dnscrypt-proxy.service}}:
 
 
  [Unit]
 
  [Unit]
 
  Description=A tool for securing communications between a client and a DNS resolver.
 
  Description=A tool for securing communications between a client and a DNS resolver.
Line 25: Line 20:
 
  # Only needed if you use pdnsd, other caching DNS servers can go here. Could be ignored too.
 
  # Only needed if you use pdnsd, other caching DNS servers can go here. Could be ignored too.
 
  #Before=pdnsd.service
 
  #Before=pdnsd.service
+
  [Service]
[Service]
+
 
  EnvironmentFile=/etc/conf.d/dnscrypt-proxy
 
  EnvironmentFile=/etc/conf.d/dnscrypt-proxy
 
  ExecStart=/usr/bin/dnscrypt-proxy \
 
  ExecStart=/usr/bin/dnscrypt-proxy \
Line 36: Line 30:
 
  Restart=on-abort
 
  Restart=on-abort
 
   
 
   
[Install]
+
  [Install]
 
  WantedBy=multi-user.target
 
  WantedBy=multi-user.target
 
 
With this setup, it will be necessary to alter your {{ic|/etc/resolv.conf}} file and replace your current set of resolver addresses with:
 
With this setup, it will be necessary to alter your {{ic|/etc/resolv.conf}} file and replace your current set of resolver addresses with:
 
  nameserver 127.0.0.1
 
  nameserver 127.0.0.1
 
 
To prevent [[dhcpcd]] from altering your DNS settings add {{ic|nohook resolv.conf}} to {{ic|/etc/dhcpcd.conf}}
 
To prevent [[dhcpcd]] from altering your DNS settings add {{ic|nohook resolv.conf}} to {{ic|/etc/dhcpcd.conf}}
 
 
You may also wish to write-protect {{ic|/etc/resolv.conf}} by setting the immutable attribute:
 
You may also wish to write-protect {{ic|/etc/resolv.conf}} by setting the immutable attribute:
 
  # chattr +i /etc/resolv.conf
 
  # chattr +i /etc/resolv.conf
 
 
== Starting ==
 
== Starting ==
Available as a [[systemd]] .service: {{ic|dnscrypt-proxy.service}}
+
Available as a [[systemd]] service: {{ic|dnscrypt-proxy.service}}
 
+
 
== Tips and tricks ==
 
== Tips and tricks ==
 +
==== Using DNSCrypt in combination with [[Unbound]] ====
 +
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.<br>Install {{Pkg|unbound}} from the [[official repositories]] and add the following lines to the end of the {{ic|server}} section in {{ic|/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 {{ic|unbound.service}}. Then configure DNScrypt to match that IP and port on the lines in {{ic|/etc/config.d/dnscrypt-proxy}}:
 +
DNSCRYPT_LOCALIP=127.0.0.1
 +
DNSCRYPT_LOCALPORT=40
 +
Restart {{ic|dnscrypt-proxy.service}} to reread the changes.
 
==== Enable EDNS0 ====
 
==== Enable EDNS0 ====
 
[https://en.wikipedia.org/wiki/Extension_mechanisms_for_DNS Extension Mechanisms for DNS] that, among other things, allows a client to specify how large a reply over UDP can be.
 
[https://en.wikipedia.org/wiki/Extension_mechanisms_for_DNS 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 {{ic|/etc/resolv.conf}}:
 
Add the following line to your {{ic|/etc/resolv.conf}}:
 
  options edns0
 
  options edns0

Revision as of 11:34, 23 February 2014

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

By default dnscrypt-proxy is pre-configured in /etc/conf.d/dnscrypt-proxy to accept incoming requests on 127.0.0.1 to an OpenDNS resolver:

DNSCRYPT_LOCALIP=127.0.0.1
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

The above file is read by /usr/lib/systemd/system/dnscrypt-proxy.service:

[Unit]
Description=A tool for securing communications between a client and a DNS resolver.
After=network.target
# Only needed if you use pdnsd, other caching DNS servers can go here. Could be ignored too.
#Before=pdnsd.service
 [Service]
EnvironmentFile=/etc/conf.d/dnscrypt-proxy
ExecStart=/usr/bin/dnscrypt-proxy \
       --local-address=${DNSCRYPT_LOCALIP}:${DNSCRYPT_LOCALPORT} \
   --resolver-address=${DNSCRYPT_RESOLVERIP}:${DNSCRYPT_RESOLVERPORT} \
   --provider-name=${DNSCRYPT_PROVIDER_NAME} \
   --provider-key=${DNSCRYPT_PROVIDER_KEY} \
       --user=${DNSCRYPT_USER}
Restart=on-abort

 [Install]
WantedBy=multi-user.target

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

nameserver 127.0.0.1

To prevent dhcpcd from altering your DNS settings add nohook resolv.conf to /etc/dhcpcd.conf You may also wish to write-protect /etc/resolv.conf by setting the immutable attribute:

# chattr +i /etc/resolv.conf

Starting

Available as a systemd service: dnscrypt-proxy.service

Tips and tricks

Using DNSCrypt in combination with Unbound

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.
Install unbound from the official repositories 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 that IP and port on the lines in /etc/config.d/dnscrypt-proxy:

DNSCRYPT_LOCALIP=127.0.0.1
DNSCRYPT_LOCALPORT=40

Restart dnscrypt-proxy.service to reread the changes.

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"

See also