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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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<!ENTITY TIMESTAMP "2011-08-08">
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<!ENTITY TIMESTAMP "2021-02-03">
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<!ENTITY % common SYSTEM "common.ent">
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<firstname>Björn</firstname>
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<surname>Påhlsson</surname>
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<email>belorn@fukt.bsnet.se</email>
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<email>belorn@recompile.se</email>
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<firstname>Teddy</firstname>
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<surname>Hogeborn</surname>
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<email>teddy@fukt.bsnet.se</email>
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<email>teddy@recompile.se</email>
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<holder>Teddy Hogeborn</holder>
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<holder>Björn Påhlsson</holder>
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The computers run a small client program in the initial RAM disk
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environment which will communicate with a server over a network.
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All network communication is encrypted using TLS. The clients
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are identified by the server using an OpenPGP key; each client
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are identified by the server using a TLS public key; each client
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has one unique to it. The server sends the clients an encrypted
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password. The encrypted password is decrypted by the clients
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using the same OpenPGP key, and the password is then used to
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using a separate OpenPGP key, and the password is then used to
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unlock the root file system, whereupon the computers can
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continue booting normally.
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<refsect1 id="introduction">
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<title>INTRODUCTION</title>
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<!-- This paragraph is a combination and paraphrase of two
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quotes from the 1995 movie “The Usual Suspects”. -->
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You know how it is. You’ve heard of it happening. The Man
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comes and takes away your servers, your friends’ servers, the
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servers of everybody in the same hosting facility. The servers
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So, at boot time, the Mandos client will ask for its encrypted
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data over the network, decrypt it to get the password, use it to
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decrypt the root file, and continue booting.
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data over the network, decrypt the data to get the password, use
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the password to decrypt the root file system, and the client can
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then continue booting.
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Now, of course the initial RAM disk image is not on the
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long, and will no longer give out the encrypted key. The timing
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here is the only real weak point, and the method, frequency and
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timeout of the server’s checking can be adjusted to any desired
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(The encrypted keys on the Mandos server is on its normal file
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No. The server only gives out the passwords to clients which
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have <emphasis>in the TLS handshake</emphasis> proven that
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they do indeed hold the OpenPGP private key corresponding to
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they do indeed hold the private key corresponding to that
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<refsect2 id="sniff">
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<title>How about sniffing the network traffic and decrypting it
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later by physically grabbing the Mandos client and using its
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We only use <acronym>PFS</acronym> (Perfect Forward Security)
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key exchange algorithms in TLS, which protects against this.
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<refsect2 id="fakeping">
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<title>Faking ping replies?</title>
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<refsect2 id="fakecheck">
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<title>Faking checker results?</title>
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The default for the server is to use
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If the Mandos client does not have an SSH server, the default
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is for the Mandos server to use
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<quote><literal>fping</literal></quote>, the replies to which
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could be faked to eliminate the timeout. But this could
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easily be changed to any shell command, with any security
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measures you like. It could, for instance, be changed to an
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SSH command with strict keychecking, which could not be faked.
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Or IPsec could be used for the ping packets, making them
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measures you like. If the Mandos client
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<emphasis>has</emphasis> an SSH server, the default
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configuration (as generated by
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<command>mandos-keygen</command> with the
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<option>--password</option> option) is for the Mandos server
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to use an <command>ssh-keyscan</command> command with strict
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keychecking, which can not be faked. Alternatively, IPsec
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could be used for the ping packets, making them secure.
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plugin requirements.
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<refsect1 id="systemd">
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<title>SYSTEMD</title>
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More advanced startup systems like <citerefentry><refentrytitle
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>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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already have their own plugin-like mechanisms for allowing
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multiple agents to independently retrieve a password and deliver
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it to the subsystem requesting a password to unlock the root
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file system. On these systems, it would make no sense to run
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<citerefentry><refentrytitle>plugin-runner</refentrytitle
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><manvolnum>8mandos</manvolnum></citerefentry>, the plugins of
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which would largely duplicate the work of (and conflict with)
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the existing systems prompting for passwords.
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As for <citerefentry><refentrytitle>systemd</refentrytitle
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><manvolnum>1</manvolnum></citerefentry> in particular, it has
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url="https://systemd.io/PASSWORD_AGENTS/">Password
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Agents</ulink> system. Mandos uses this via its
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<citerefentry><refentrytitle>password-agent</refentrytitle
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><manvolnum>8mandos</manvolnum></citerefentry> program, which is
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run instead of <citerefentry><refentrytitle
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>plugin-runner</refentrytitle><manvolnum>8mandos</manvolnum
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></citerefentry> when <citerefentry><refentrytitle
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>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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is used during system startup.
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<xi:include href="bugs.xml"/>
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<refsect1 id="see_also">
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<title>SEE ALSO</title>
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<manvolnum>8</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>plugin-runner</refentrytitle>
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<manvolnum>8mandos</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>password-agent</refentrytitle>
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<manvolnum>8mandos</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>mandos-client</refentrytitle>
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<manvolnum>8mandos</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>password-prompt</refentrytitle>
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intro.xml
