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