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DNSCrypt

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Revision as of 07:26, 27 April 2016 by >Se7en (Undo revision 32005 by Se7en (talk))
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See also Anonymising yourself

Dnscrypt.png

DNSCrypt is a local DNS resolver and uses elliptic-curve cryptography when passing messages to and from the DNS server—which is extremely useful for mitigating MITM attacks on DNS. It is best used alongside a caching DNS server like Unbound.

Only a few servers are known to currently support DNSCrypt, however, adoption is growing.

Installation

Unix-like

Requirements & dependencies

`--  dev-libs/libsodium
`--  net-libs/ldns
`--  virtual/pkgconfig
`--  sys-apps/systemd (optional!)

Arch users can install dnscrypt-proxy and set it up manually, or install dnscrypt-autoinstall from the AUR. Gentoo users can easily compile DNSCrypt from scratch from the main repository. Debian users can install it from the package dnscrypt-proxy, but only in testing or unstable.

Building

  1. git clone git://github.com/jedisct1/dnscrypt-proxy.git
  2. cd dnscrypt-proxy
  3. ./autogen.sh
  4. ./configure --prefix=/usr
  5. make
  6. sudo make install
Remove systemd as a dependency (optional)

In newer versions, the configure file detects if you have Systemd or not. However, if you have version 1.6 systemd needs be removed from the software by leaving its references out of the configure document before compiling.

Relevant lines can be found around 3258 to 3288 of the configure document. End result should look something like this: 

#Manual systemd patch. Go away NSA.
have_systemd=no
HAVE_SYSTEMD_TRUE=
HAVE_SYSTEMD_FALSE='#'

#Check whether --with-systemd was given.
#if test "${with_systemd+set}" = set; then :
#  withval=$with_systemd;
#fi
#
#if test "x$with_systemd" = "xyes"; then :
#
#  PKG_CHECK_MODULES(SYSTEMD, libsystemd, have_systemd=yes,
#    PKG_CHECK_MODULES([SYSTEMD_DAEMON], [libsystemd-daemon], [have_systemd=yes], [have_systemd=no])
#  )
#  case $with_systemd:$have_systemd in #(
#  yes:no) :
#    as_fn_error $? "systemd expected but libsystemd not found" #"$LINENO" 5 ;; #(
#  *:yes) :
#
#$as_echo "#define HAVE_LIBSYSTEMD 1" >>confdefs.h
#
#   ;; #(
#  *) :
#     ;;
#esac
#
#fi
# if test "x$have_systemd" = "xyes"; then
#  HAVE_SYSTEMD_TRUE=
#  HAVE_SYSTEMD_FALSE='#'
#else
#  HAVE_SYSTEMD_TRUE='#'
#  HAVE_SYSTEMD_FALSE=
#fi


Now run echo /usr/local/lib > /etc/ld.so.conf.d/usr_local_lib.conf, sudo ldconfig and ./configure, then make and finally sudo make install.

Windows

Use SimpleDNSCrypt, it just werks. If it doesn't, go talk to the developer.

iOS

You will need a jailbroken iOS device (>=5.1.1) in order to install DNSCrypt.

  1. Download the pre-compiled binary for iOS;
  2. Copy the {bin,sbin,share} directories of the archive into the {bin,sbin,share} directories of the device;

Configuration

Linux

If you would rather run the commands yourself at boot time, this section is for you. However, the following step is common amongst all Linux distros: you must edit your /etc/resolv.conf file to look like this: 

/etc/resolv.conf
domain home
nameserver <the DNSCrypt you picked for --local-address>
options edns0

Lock it with sudo chattr +i /etc/resolv.conf, and then, either move on to systemd/OpenRC, or run the following script every time you boot up your PC: 

sudo dnscrypt-proxy --local-address=<ip>[:port] --daemonize --resolver-address=<Server address> --provider-name=<Provider name> --provider-key=<Public key> --edns-payload-size=4096 --logfile=/var/log/dnscrypt-proxy.log

Note: It is recommended to use 127.0.0.1 or 127.0.0.2, and port 40 instead of 53, should you ever want to use Unbound or Dnsmasq with it, without too much hassle.

Tip: Security considerations.

systemd

If you didn't remove the systemd depedency, the source distribution includes the dnscrypt-proxy.socket and dnscrypt-proxy.service files. As such, in order to activate them, you need only run systemctl start dnscrypt-proxy.socket and systemctl start dnscrypt-proxy.service.

To ensure it starts automagically every time you boot up your PC, systemctl enable dnscrypt-proxy.socket and systemctl enable dnscrypt-proxy.service.

You can check if it's running by issuing systemctl status dnscrypt-proxy.service.

Note: DNSCrypt's systemd socket uses port 53 by default. You can easily change that at will.

OpenRC

/etc/init.d/dnscrypt-proxy
#!/sbin/runscript

## Note: This may need to be changed to /usr/bin/runscript depending on system. If you use
## a Debian fork that does not have Systemd, the runscript program can be installed using the package
## ``minicom" through apt

# This script is Copyright (C) 1999-2014 Gentoo Foundation
# Distributed under the terms of the GNU General Public License v2
 
  # $Id$
 
 DNSCRYPT_LOGFILE=${DNSCRYPT_LOGFILE:-/var/log/dnscrypt-proxy.log}
 
 rundir=${rundir:-/var/run/dnscrypt-proxy}
 pidfile=${pidfile:-${rundir}/dnscrypt-proxy.pid}
 rundir=${rundir:-/var/run/dnscrypt-proxy}
 runas_user=${runas_user:-dnscrypt}
 runas_group=${runas_user:-dnscrypt}
 
 depend() {
 	use net
 	before dns
 	after logger
 }
 
 start() {
 	if [ ! -d "${rundir}" ]; then
 		mkdir "${rundir}"
 		if [ -n "${runas_user}" ]; then
 			touch "${DNSCRYPT_LOGFILE}"
 			chown ${runas_user}:${runas_group} "${DNSCRYPT_LOGFILE}"
 			chown -R ${runas_user}:${runas_group} "${rundir}"
 		fi
 	fi
 
 	ebegin "Starting dnscrypt-proxy"
 	start-stop-daemon --start --quiet \
 		--exec /usr/sbin/dnscrypt-proxy \
 		-- \
 		--pidfile="${pidfile}" \
 		--logfile="${DNSCRYPT_LOGFILE}" \
 		--daemonize --user=${runas_user} \
 		--local-address=${DNSCRYPT_LOCALIP}:${DNSCRYPT_LOCALPORT} \
 		--resolver-address=${DNSCRYPT_RESOLVERIP}:${DNSCRYPT_RESOLVERPORT} \
 		--provider-name=${DNSCRYPT_PROVIDER_NAME} \
 		--provider-key=${DNSCRYPT_PROVIDER_KEY}
 	eend $?
 }
 
 stop() {
 	ebegin "Stopping dnscrypt-proxy"
 	start-stop-daemon --stop --quiet --exec /usr/sbin/dnscrypt-proxy
 	eend $?
 }

You will need to make it executable, sudo chmod +x /etc/init.d/dnscrypt-proxy.

This init script will of course require a configuration file, located here /etc/conf.d/dnscrypt-proxy file. Pick two servers (one will work as the fallback server), whilst making sure they are compatible with the options you will want to use later on (DNSSEC with unbound, for instance), and add the following text: 

/etc/conf.d/dnscrypt-proxy
DNSCRYPT_LOCALIP=127.0.0.1
DNSCRYPT_LOCALPORT=40
DNSCRYPT_USER=dnscrypt
 
DNSCRYPT_PROVIDER_NAME=
DNSCRYPT_PROVIDER_KEY=
DNSCRYPT_RESOLVERIP=
 
DNSCRYPT_PROVIDER_NAME=
DNSCRYPT_PROVIDER_KEY=
DNSCRYPT_RESOLVERIP=

DNSCRYPT_OPTIONS="--edns-payload-size=4096"
 
DNSCRYPT_RESOLVERPORT=443

Alternatively, you could use this script to get information directly from the csv file containing the data from /usr/share/dnscrypt-proxy (you would need to move the csv there yourself) 

/etc/init.d/dnscrypt-proxy
#!/sbin/runscript


## Note: This may need to be changed to /usr/bin/runscript depending on system. If you use
## a Debian fork that does not have Systemd, the runscript program can be installed using the package
## ``minicom" through apt


# Copyright 1999-2014 Gentoo Foundation
# Distributed under the terms of the GNU General Public License v2
# $Id$

DNSCRYPT_LOGFILE=${DNSCRYPT_LOGFILE:-/var/log/dnscrypt-proxy.log}
DNSCRYPT_RESOLVERS_LIST=${DNSCRYPT_RESOLVERS_LIST:-/usr/share/dnscrypt-proxy/dnscrypt-resolvers.csv}

rundir=${rundir:-/var/run/dnscrypt-proxy}
pidfile=${pidfile:-${rundir}/dnscrypt-proxy.pid}
rundir=${rundir:-/var/run/dnscrypt-proxy}
runas_user=${runas_user:-dnscrypt}
runas_group=${runas_user:-dnscrypt}

depend() {
	use net
	before dns
	after logger
}

start() {
	if [ ! -d "${rundir}" ]; then
		mkdir "${rundir}"
		if [ -n "${runas_user}" ]; then
			touch "${DNSCRYPT_LOGFILE}"
			chown ${runas_user}:${runas_group} "${DNSCRYPT_LOGFILE}"
			chown -R ${runas_user}:${runas_group} "${rundir}"
		fi
	fi

	if [ -n "$DNSCRYPT_RESOLVER_NAME" -a -n "$DNSCRYPT_RESOLVERIP" ]; then
		eerror "You must set exactly one of DNSCRYPT_RESOLVER_NAME or DNSCRYPT_RESOLVERIP!"
		return 1
	elif [ -n "$DNSCRYPT_RESOLVER_NAME" ]; then
		resolver_opts="--resolvers-list=${DNSCRYPT_RESOLVERS_LIST} --resolver-name=${DNSCRYPT_RESOLVER_NAME}"
	elif [ -n "$DNSCRYPT_RESOLVERIP" ]; then
		resolver_opts="--resolver-address=${DNSCRYPT_RESOLVERIP}:${DNSCRYPT_RESOLVERPORT} --provider-name=${DNSCRYPT_PROVIDER_NAME} --provider-key=${DNSCRYPT_PROVIDER_KEY}"
	else
		eerror "You must set exactly one of DNSCRYPT_RESOLVER_NAME or DNSCRYPT_RESOLVERIP!"
		return 1
	fi

	ebegin "Starting dnscrypt-proxy"
	start-stop-daemon --start --quiet \
		--exec /usr/sbin/dnscrypt-proxy \
		-- \
		${DNSCRYPT_OPTIONS} \
		--pidfile="${pidfile}" \
		--logfile="${DNSCRYPT_LOGFILE}" \
		--daemonize --user=${runas_user} \
		--local-address=${DNSCRYPT_LOCALIP}:${DNSCRYPT_LOCALPORT} \
		$resolver_opts
	eend $?
}

stop() {
	ebegin "Stopping dnscrypt-proxy"
	start-stop-daemon --stop --quiet --exec /usr/sbin/dnscrypt-proxy
	eend $?
}

Make sure to substitute where appropriate. You will also have to manually create a user called dnscrypt, with: 

/etc/passwd
dnscrypt:x:117:991:/var/empty:/sbin/nologin

You'll also have to create a group: 

/etc/group
...
dnscrypt:x:991:

To activate the init script, issue sudo rc-update add dnscrypt-proxy.

Mac OS X

Use the dnscrypt-osxclient.

Android

iOS

  1. Edit the org.dnscrypt.osx.DNSCryptProxy.plist file to set the resolver name to use, by editing this string <string>--resolver-name=***CHANGETHIS***</string>;
  2. Copy the org.dnscrypt.osx.DNSCryptProxy.plist file into /Libary/LaunchDaemons on the device;

To get it working, simply:

  1. Reboot or type launchctl load org.dnscrypt.osx.DNSCryptProxy.plist;
  2. Change your wifi settings to use 127.0.0.1 as a DNS resolver;
  3. Enjoy being less susceptible to MITM attacks whilst on public WiFis.

Additional considerations

Picking a server

One must take a few considerations when picking a server:

  • Does it keep logs?
  • Does it support the DNSCrypt protocol specification?
  • Does it support DNSSEC (assuming you want to use it in conjunction with DNSCrypt, and use Unbound to enforce it)?
  • Is the latency low enough?
  • Is the company or individual running the server trustworthy, or do they appear to have ulterior motives?

As it stands, I trust the dnscrypt-eu servers. However, if you have no need for DNSSEC support, you can look into the various cryptostorm servers (if you're not in Europe), or the OpenNIC ones, if you'd like to make use of their extra TLDs.

Fallback DNS servers

It is also recommended to add a second, or even a third nameserver (that you know works) to your resolv.conf file. The default maximum you can have is 6, but you can change this number to whatever you want, by hacking MAXDNSRCH and defdname in resolv.h and recompiling the then patched libc. A resolv.conf (with more than 6 nameservers) may look like this.

Note: The fallback servers will _NOT_ go through DNSCrypt, meaning they will not be encrypted and your local network will be vulnerable to DNS spoofing (unless you're visiting a DNSSEC page and using Unbound or something else to enforce it). In order to have DNSCrypt fallback servers, you'll need to run multiple instances of the program.

Sandboxing

It is possible to sandbox DNSCrypt, and even recommended. You can also create an extra user/group to run it, with no privileges, and no home folder for an additional layer of protection.

To sandbox DNSCrypt, simply install firejail, and edit your systemd/OpenRC scripts, adding the prefix 'firejail' before dnscrypt. Firejail comes bundled with a profile for DNSCrypt and many more, which you can analyse, and even edit, by issuing vim /etc/firejail.

Troubleshooting

Run hostip -r 127.0.0.1 example.com. If that outputs an IP, then DNSCrypt is working and the problem lies with whatever DNS cache you're using (most likely Dnsmasq or Unbound not forwarding the right address/port). If not, then your DNS server might be down, in which case you should issue sudo chattr -i /etc/resolv.conf to unlock your resolv.conf, and temporarily change the nameserver to a DNS server of your choice until you fix the issue (not necessary if you have fall-back DNS servers, as you should).

If none of this fixes it, look at /var/log/dnscrypt-proxy.log and figure it out yourself, or are you not a true /g/entooman?

Tip: If you are using Unbound, or another caching DNS server of that sort, it is possible something is wrong with it and thus, you should also visit that program's log file and look for potential errors or warnings.

External links

Retrieved from "https://igwiki.lyci.de/index.php?title=DNSCrypt&oldid=3853"