doc/apt-secure.8.xml

   1 <?xml version="1.0" encoding="utf-8" standalone="no"?>
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
   4
   5 <!ENTITY % aptent SYSTEM "apt.ent">
   6 %aptent;
   7
   8 <!ENTITY % aptverbatiment SYSTEM "apt-verbatim.ent">
   9 %aptverbatiment;
  10
  11 <!ENTITY % aptvendor SYSTEM "apt-vendor.ent">
  12 %aptvendor;
  13 ]>
  14
  15 <refentry>
  16  <refentryinfo>
  17    &apt-author.jgunthorpe;
  18    &apt-author.team;
  19    &apt-email;
  20    &apt-product;
  21    <!-- The last update date -->
  22    <date>2012-06-09T00:00:00Z</date>
  23  </refentryinfo>
  24
  25  <refmeta>
  26    <refentrytitle>apt-secure</refentrytitle>
  27    <manvolnum>8</manvolnum>
  28    <refmiscinfo class="manual">APT</refmiscinfo>
  29  </refmeta>
  30
  31 <!-- NOTE: This manpage has been written based on the
  32      Securing Debian Manual ("Debian Security
  33      Infrastructure" chapter) and on documentation
  34      available at the following sites:
  35      http://wiki.debian.net/?apt06
  36      http://www.syntaxpolice.org/apt-secure/
  37      http://www.enyo.de/fw/software/apt-secure/
  38 -->
  39 <!-- TODO: write a more verbose example of how it works with
  40      a sample similar to
  41      http://www.debian-administration.org/articles/174
  42      ?
  43 -->
  44
  45
  46  <!-- Man page title -->
  47  <refnamediv>
  48     <refname>apt-secure</refname>
  49     <refpurpose>Archive authentication support for APT</refpurpose>
  50  </refnamediv>
  51
  52  <refsect1><title>Description</title>
  53    <para>
  54    Starting with version 0.6, <command>apt</command> contains code
  55    that does signature checking of the Release file for all
  56    archives. This ensures that packages in the archive can't be
  57    modified by people who have no access to the Release file signing
  58    key.
  59    </para>
  60
  61    <para>
  62    If a package comes from a archive without a signature, or with a
  63    signature that apt does not have a key for, that package is
  64    considered untrusted, and installing it will result in a big
  65    warning. <command>apt-get</command> will currently only warn
  66    for unsigned archives; future releases might force all sources
  67    to be verified before downloading packages from them.
  68    </para>
  69
  70    <para>
  71    The package frontends &apt-get;, &aptitude; and &synaptic; support this new
  72    authentication feature.
  73    </para>
  74 </refsect1>
  75
  76  <refsect1><title>Trusted archives</title>
  77
  78    <para>
  79    The chain of trust from an apt archive to the end user is made up of
  80    several steps. <command>apt-secure</command> is the last step in
  81    this chain; trusting an archive does not mean that you trust its
  82    packages not to contain malicious code, but means that you
  83    trust the archive maintainer. It's the archive maintainer's
  84    responsibility to ensure that the archive's integrity is preserved.
  85    </para>
  86
  87    <para>apt-secure does not review signatures at a
  88    package level. If you require tools to do this you should look at
  89    <command>debsig-verify</command> and
  90    <command>debsign</command> (provided in the debsig-verify and
  91    devscripts packages respectively).</para>
  92
  93    <para>
  94    The chain of trust in Debian starts when a maintainer uploads a new
  95    package or a new version of a package to the Debian archive. In
  96    order to become effective, this upload needs to be signed by a key
  97    contained in the Debian Maintainers keyring (available in
  98    the debian-keyring package). Maintainers' keys are signed by
  99    other maintainers following pre-established procedures to
 100    ensure the identity of the key holder.
 101    </para>
 102
 103    <para>
 104    Once the uploaded package is verified and included in the archive,
 105    the maintainer signature is stripped off, and checksums of the package
 106    are computed and put in the Packages file. The checksums of all of the
 107    Packages files are then computed and put into the Release file. The
 108    Release file is then signed by the archive key for this &keyring-distro; release,
 109    and distributed alongside the packages and the Packages files on
 110    &keyring-distro; mirrors. The keys are in the &keyring-distro; archive keyring
 111    available in the &keyring-package; package.
 112    </para>
 113
 114    <para>
 115    End users can check the signature of the Release file, extract a checksum
 116    of a package from it and compare it with the checksum of the package
 117    they downloaded by hand - or rely on APT doing this automatically.
 118    </para>
 119
 120    <para>Notice that this is distinct from checking signatures on a
 121    per package basis. It is designed to prevent two possible attacks:
 122    </para>
 123
 124     <itemizedlist>
 125        <listitem><para><literal>Network "man in the middle"
 126        attacks</literal>. Without signature checking, malicious
 127        agents can introduce themselves into the package download process and
 128        provide malicious software either by controlling a network
 129        element (router, switch, etc.) or by redirecting traffic to a
 130        rogue server (through ARP or DNS spoofing
 131        attacks).</para></listitem>
 132
 133        <listitem><para><literal>Mirror network compromise</literal>.
 134         Without signature checking, a malicious agent can compromise a
 135         mirror host and modify the files in it to propagate malicious
 136         software to all users downloading packages from that
 137         host.</para></listitem>
 138     </itemizedlist>
 139
 140    <para>However, it does not defend against a compromise of the
 141    Debian master server itself (which signs the packages) or against a
 142    compromise of the key used to sign the Release files. In any case,
 143    this mechanism can complement a per-package signature.</para>
 144 </refsect1>
 145
 146  <refsect1><title>User configuration</title>
 147    <para>
 148    <command>apt-key</command> is the program that manages the list
 149    of keys used by apt. It can be used to add or remove keys, although
 150    an installation of this release will automatically contain the
 151    default Debian archive signing keys used in the Debian package
 152    repositories.
 153    </para>
 154    <para>
 155    In order to add a new key you need to first download it
 156    (you should make sure you are using a trusted communication channel
 157    when retrieving it), add it with <command>apt-key</command> and
 158    then run <command>apt-get update</command> so that apt can download
 159    and verify the <filename>InRelease</filename> or <filename>Release.gpg</filename>
 160    files from the archives you have configured.
 161    </para>
 162 </refsect1>
 163
 164 <refsect1><title>Archive configuration</title>
 165    <para>
 166    If you want to provide archive signatures in an archive under your
 167    maintenance you have to:
 168    </para>
 169
 170      <itemizedlist>
 171        <listitem><para><emphasis>Create a toplevel Release
 172        file</emphasis>,  if it does not exist already. You can do this
 173        by running <command>apt-ftparchive release</command>
 174        (provided in apt-utils).</para></listitem>
 175
 176       <listitem><para><emphasis>Sign it</emphasis>. You can do this by running
 177       <command>gpg --clearsign -o InRelease Release</command> and
 178       <command>gpg -abs -o Release.gpg Release</command>.</para></listitem>
 179
 180       <listitem><para><emphasis>Publish the key fingerprint</emphasis>,
 181       that way your users will know what key they need to import in
 182       order to authenticate the files in the
 183       archive.</para></listitem>
 184
 185     </itemizedlist>
 186
 187     <para>Whenever the contents of the archive change (new packages
 188     are added or removed) the archive maintainer has to follow the
 189     first two steps outlined above.</para>
 190
 191 </refsect1>
 192
 193 <refsect1><title>See Also</title>
 194 <para>
 195 &apt-conf;, &apt-get;, &sources-list;, &apt-key;, &apt-ftparchive;,
 196 &debsign;, &debsig-verify;, &gpg;
 197 </para>
 198
 199 <para>For more background information you might want to review the
 200 <ulink
 201 url="http://www.debian.org/doc/manuals/securing-debian-howto/ch7">Debian
 202 Security Infrastructure</ulink> chapter of the Securing Debian Manual
 203 (available also in the harden-doc package) and the
 204 <ulink url="http://www.cryptnet.net/fdp/crypto/strong_distro.html"
 205 >Strong Distribution HOWTO</ulink> by V. Alex Brennen.  </para>
 206
 207 </refsect1>
 208
 209  &manbugs;
 210  &manauthor;
 211
 212 <refsect1><title>Manpage Authors</title>
 213
 214 <para>This man-page is based on the work of Javier Fernández-Sanguino
 215 Peña, Isaac Jones, Colin Walters, Florian Weimer and Michael Vogt.
 216 </para>
 217
 218 </refsect1>
 219
 220
 221 </refentry>
 222