christiansaga.de

As a long time PGP user I wanted to improve the key landscape and offer my public key via DANE. This is quite simple, if you have a DNS host, that supports DNSSEC and the different needed DANE types. (Note: I use core-networks.de)

The principle behind this: You publish your PGP key in your signed DNS and by that a correctly configured mail system could opt into sending you encrypted E-Mails even without having exchanged keys before.

I have tried to use the gpg2 function --print-dane-records (available from 2.1.9 upwards), however could not generate a usable data part of the DNS record via this.

So what is the solution

As a prerequisite you need to have created your own PGP keys with the E-Mail you want to use as an User ID. Note: I am only doing a per E-Mail Setup. Use the following website: https://www.huque.com/bin/openpgpkey

Generate an OPENPGPKEY and the output pretty much does the trick. The generated output is sorted as follows:

• Owner Name goes into the record. Be careful, if your DNS provider automatically adds the domain.If you used --print-dane-records you need to concatenate the ID of the key (before TYPE61) and string after $ORIGIN The syntax is <SHA256 hash of your e-mail name before the @>._openpgpkey.<your domain>

• Out of Generated DNS OPENPGPKEY Record you take the part within the () into the data part of the record. Here you need to transform the key into one line string. If you used --print-dane-records, I discarded the data part, as I could not get it to work. Simply use your key data exported with ASCII armor (-a parameter) without the last line. Of course leaving headers and footers out as well.

• The type is OPENPGPKEY

• Class is IN

• TTL you can set on a decent value. For testing I used a hour.

To test the setup use

dig OPENPGPKEY <owner name goes here>

This will simply send back the data block and test the DNS setup. To test the DANE lookup do the following

gpg2 --auto-key-locate clear,dane,local -v --locate-key <your e-mail goes here>

This gives quite a good feedback on the setup and tells you if the key was fetched via DANE or not.

To have a more comfortable way of receiving messages by my servers, I wanted all my root E-Mails to be forwarded to my mobile via XMPP. I only have a limited exim4 on my machine running, configured for local mail delivery only.

So what is the solution

First install sendxmpp with apt-get install sendxmpp, then create the config file as /etc/sendxmpp.conf and insert XMPP credentials:

<sender>@<sender_server>:<port> <password>

Set the right permissions chmod 600 /etc/sendxmpp.conf and owner chown Debian-exim:Debian-exim /etc/sendxmpp.conf

Then create a script to call sendxmpp /usr/sbin/mail2xmpp. It might be that you could put this completely into the alias, however I decided to use the script. Exchange your receiving ID. -t enables the TLS connection for sending the message.

#!/bin/bash
echo "$(cat)" | sendxmpp -t -f /etc/sendxmpp.conf <receiver>@<receiving_server>

Make the script executable chmod 755 /usr/sbin/mail2xmpp and create the alias for the user, which E-Mails you want to forward in /etc/aliases:

# /etc/aliases
root:,|/usr/local/bin/mail2xmpp

To activate pipe forwarding we have to create /etc/exim4/exim4.conf.localmacros SoWhatIsTheSolution

SYSTEM_ALIASES_PIPE_TRANSPORT = address_pipe

After that run newaliases and service exim4 restart for config to take effect. Now you should be able to test if it works, by simply sending a local test E-Mail to user root.

As already described in my previous post Headless Debian install via SSH, I am dealing with a headless system. As I am encrypting my system and drives with LUKS, I need a way to enter the password in case of a reboot.

So what is the solution

First install Dropbear on the server by apt-get install dropbear. Then configure initramfs network usage; edit /etc/initramfs-tools/initramfs.conf. You probably have to add the lines for dropbear and update the device string. This configuration is using DHCP to obtain an IP, if you have a static configuration, use: IP=<SERVER-IP>::<STANDARD-GATEWAY>:<SUBNETMASK>:<HOSTNAME>:eth0:off

#
# DROPBEAR: [ y | n ]
#
# Use dropbear if available.
#
DROPBEAR=y

DEVICE=eth0
IP=:::::eth0:dhcp

Next, delete the standard private and public keys on the server

rm /etc/initramfs-tools/root/.ssh/id_rsa
rm /etc/initramfs-tools/root/.ssh/id_rsa.pub

Then create your own key pair (we assume you use id_rsa as a name) on your client machine and upload it to the server.

ssh-keygen
scp ~/.ssh/id_rsa.pub myuser@debian_headless:id_rsa.pub

After that, log in to the server and add the key to authorized_key file an remove the public key on the server.

ssh myuser@debian_headless
sudo sh -c "cat id_rsa.pub >> /etc/initramfs-tools/root/.ssh/authorized_keys"
rm id_rsa.pub

Now we need to update initramfs and grub by update-initramfs -u -k all and update-grub2

On some configurations the network won’t get reconfigured on runtime values, hence we need to trigger an update. Edit /etc/network/interfaces and add as first line of the primary interface pre-up ip addr flush dev eth0

Restart server and log in from your client with ssh -i ~/.ssh/id_rsa root@<server-ip> to set the password to unlock

echo -n "<LUKS encryption password>" > /lib/cryptsetup/passfifo
exit

EDIT: on newer systems a cryptroot-unlock will suffice.

The server should now boot normally and regular SSH should come up.

Optional

You can also create a little script for the passphrase in /etc/initramfs-tools/hooks/unlock

#!/bin/bash
PREREQ=""
prereqs() {
  echo "$PREREQ"
}

case $1 in
prereqs)
prereqs
exit 0
;;
esac

. /usr/share/initramfs-tools/hook-functions

cat > "${DESTDIR}/root/unlock" << EOF #!/bin/sh /lib/cryptsetup/askpass 'passphrase: ' > /lib/cryptsetup/passfifo
EOF

chmod u+x "${DESTDIR}/root/unlock"

exit 0

Do not forget to make it executable with chmod +x /etc/initramfs-tools/hooks/unlock and update initramfs with update-initramfs -u -k all and update-grub2

Having build my own NAS system recently, I realised I do not have any monitors or keyboards at home anymore. Hence installing Debian will be hard. I looked around and the solution would be a headless install via ssh.

This post is based on some work from S.G. Vulcan’s post Installing Debian using only SSH His post was a good start, but I only could make it work for a Debian Jessie netinstall image after some changes.

So what is the solution

Download the latest netinstall image from Debian, I used debian-8.3.0-amd64-netinst.iso

Mount the ISO to a folder

mkdir isoorig
sudo mount -o loop -t iso9660 debian-8.3.0-amd64-netinst.iso isoorig

Copy to new folder called isonew

mkdir isonew
rsync -a -H --exclude=TRANS.TBL isoorig/ isonew/

Change the menu to load SSH on boot by default, edit isonew/isolinux/txt.cfg remove (if existing) menu default from label install and add:

label netinstall
  menu label ^Install Over SSH
  menu default
  kernel /install.amd/vmlinuz
  append auto=true vga=788 file=/cdrom/preseed.cfg initrd=/install.arm/initrd.gz locale=en_US console-keymaps-at/keymap=us

default netinstall

Create isonew/preseed.cfg file. I adapted the locale and keyboard settings for Germany and added the selection of the keyboard-configuration. This would otherwise be an open question during the install and we won’t reach the SSH startup.

Also I added a check for non-free firmware, which popped up on one of my machines which had wireless.

#### Contents of the preconfiguration file
### Localization
# Locale sets language and country.
d-i debian-installer/locale select de_DE
# Keyboard selection.
d-i console-keymaps-at/keymap select de
d-i keyboard-configuration/xkb-keymap select de
### Network configuration
# netcfg will choose an interface that has link if possible. This makes it
# skip displaying a list if there is more than one interface.
d-i netcfg/choose_interface select auto
# Any hostname and domain names assigned from dhcp take precedence over
# values set here. However, setting the values still prevents the questions
# from being shown, even if values come from dhcp.
d-i netcfg/get_hostname string newdebian
d-i netcfg/get_domain string local
# If non-free firmware is needed for the network or other hardware, you can
# configure the installer to always try to load it, without prompting. Or
# change to false to disable asking.
d-i hw-detect/load_firmware boolean true
# The wacky dhcp hostname that some ISPs use as a password of sorts.
#d-i netcfg/dhcp_hostname string radish
d-i preseed/early_command string anna-install network-console
# Setup ssh password
d-i network-console/password password install
d-i network-console/password-again password install

Recreate the isonew/md5sum.txt, it is read only, so you need to change this. Also I had better luck with creating the md5sum.txt with the changed commands below.

chmod 666 md5sum.txt
find -follow -type f -exec md5sum {} \; > md5sum.txt
chmod 444 md5sum.txt

Create ISO file to burn with xorriso. If you do not have it installed use apt-get install xorriso.

xorriso -as mkisofs -D -r -J -joliet-long -l -V "Debian headless" -b isolinux/isolinux.bin -c isolinux/boot.cat -iso-level 3 -no-emul-boot -partition_offset 16 -boot-load-size 4 -boot-info-table -isohybrid-mbr /usr/lib/syslinux/isohdpfx.bin -o ../debian-8.3.0-amd64-netinst-headless.iso ../isonew

xorriso is creating a correct partition table, which is for some reason not done with mkisofs only. The original command would work in VMs, maybe even on a cd-rom, however not for USB sticks.

The ISO can be burned to an USB stick and used to boot. It will automatically configure the network with DHCP (yes, you need to have a way to find the IP, e.g. on your router) and start SSH. The user for the ssh connection is installer the password is install.

After the upgrade of Wheezy to Jessie, Spamassassin is not added to the startup services. Hence if you were using it before in your mail setup, you will run into the following error in /var/log/syslog

spamc: connect to spamd on ::1 failed, retrying (#1 of 3): Connection refused
spamc: connect to spamd on 127.0.0.1 failed, retrying (#1 of 3): Connection refused

Debian has a similar bug filed (#764438), even after a fresh reinstall.

So what is the solution

Simply activate Spamassassin via systemctl enable spamassassin