apt-secure

APT-SECURE(8)                         APT                        APT-SECURE(8)

NAME
       apt-secure - Archive authentication support for APT

DESCRIPTION
       Starting with version 0.6, APT contains code that does signature
       checking of the Release file for all repositories. This ensures that
       data like packages in the archive can't be modified by people who have
       no access to the Release file signing key. Starting with version 1.1
       APT requires repositories to provide recent authentication information
       for unimpeded usage of the repository. Since version 1.5 changes in the
       information contained in the Release file about the repository need to
       be confirmed before APT continues to apply updates from this
       repository.

       Note: All APT-based package management front-ends like apt-get(8),
       aptitude(8) and synaptic(8) support this authentication feature, so
       this manpage uses APT to refer to them all for simplicity only.

UNSIGNED REPOSITORIES
       If an archive has an unsigned Release file or no Release file at all
       current APT versions will refuse to download data from them by default
       in update operations and even if forced to download front-ends like
       apt-get(8) will require explicit confirmation if an installation
       request includes a package from such an unauthenticated archive.

       You can force all APT clients to raise only warnings by setting the
       configuration option Acquire::AllowInsecureRepositories to true.
       Individual repositories can also be allowed to be insecure via the
       sources.list(5) option allow-insecure=yes. Note that insecure
       repositories are strongly discouraged and all options to force apt to
       continue supporting them will eventually be removed. Users also have
       the Trusted option available to disable even the warnings, but be sure
       to understand the implications as detailed in sources.list(5).

       A repository which previously was authenticated but would loose this
       state in an update operation raises an error in all APT clients
       irrespective of the option to allow or forbid usage of insecure
       repositories. The error can be overcome by additionally setting
       Acquire::AllowDowngradeToInsecureRepositories to true or for Individual
       repositories with the sources.list(5) option
       allow-downgrade-to-insecure=yes.

SIGNED REPOSITORIES
       The chain of trust from an APT archive to the end user is made up of
       several steps.  apt-secure is the last step in this chain; trusting an
       archive does not mean that you trust its packages not to contain
       malicious code, but means that you trust the archive maintainer. It's
       the archive maintainer's responsibility to ensure that the archive's
       integrity is preserved.

       apt-secure does not review signatures at a package level. If you
       require tools to do this you should look at debsig-verify and debsign
       (provided in the debsig-verify and devscripts packages respectively).

       The chain of trust in Debian starts (e.g.) when a maintainer uploads a
       new package or a new version of a package to the Debian archive. In
       order to become effective, this upload needs to be signed by a key
       contained in one of the Debian package maintainer keyrings (available
       in the debian-keyring package). Maintainers' keys are signed by other
       maintainers following pre-established procedures to ensure the identity
       of the key holder. Similar procedures exist in all Debian-based
       distributions.

       Once the uploaded package is verified and included in the archive, the
       maintainer signature is stripped off, and checksums of the package are
       computed and put in the Packages file. The checksums of all of the
       Packages files are then computed and put into the Release file. The
       Release file is then signed by the archive key for this Ubuntu release,
       and distributed alongside the packages and the Packages files on Ubuntu
       mirrors. The keys are in the Ubuntu archive keyring available in the
       ubuntu-keyring package.

       End users can check the signature of the Release file, extract a
       checksum of a package from it and compare it with the checksum of the
       package they downloaded by hand - or rely on APT doing this
       automatically.

       Notice that this is distinct from checking signatures on a per package
       basis. It is designed to prevent two possible attacks:

       o   Network "man in the middle" attacks. Without signature checking,
           malicious agents can introduce themselves into the package download
           process and provide malicious software either by controlling a
           network element (router, switch, etc.) or by redirecting traffic to
           a rogue server (through ARP or DNS spoofing attacks).

       o   Mirror network compromise. Without signature checking, a malicious
           agent can compromise a mirror host and modify the files in it to
           propagate malicious software to all users downloading packages from
           that host.

       However, it does not defend against a compromise of the master server
       itself (which signs the packages) or against a compromise of the key
       used to sign the Release files. In any case, this mechanism can
       complement a per-package signature.

INFORMATION CHANGES
       A Release file contains beside the checksums for the files in the
       repository also general information about the repository like the
       origin, codename or version number of the release.

       This information is shown in various places so a repository owner
       should always ensure correctness. Further more user configuration like
       apt_preferences(5) can depend and make use of this information. Since
       version 1.5 the user must therefore explicitly confirm changes to
       signal that the user is sufficiently prepared e.g. for the new major
       release of the distribution shipped in the repository (as e.g.
       indicated by the codename).

USER CONFIGURATION
       apt-key is the program that manages the list of keys used by APT to
       trust repositories. It can be used to add or remove keys as well as
       list the trusted keys. Limiting which key(s) are able to sign which
       archive is possible via the Signed-By in sources.list(5).

       Note that a default installation already contains all keys to securely
       acquire packages from the default repositories, so fiddling with
       apt-key is only needed if third-party repositories are added.

       In order to add a new key you need to first download it (you should
       make sure you are using a trusted communication channel when retrieving
       it), add it with apt-key and then run apt-get update so that apt can
       download and verify the InRelease or Release.gpg files from the
       archives you have configured.

REPOSITORY CONFIGURATION
       If you want to provide archive signatures in an archive under your
       maintenance you have to:

       o   Create a toplevel Release file, if it does not exist already. You
           can do this by running apt-ftparchive release (provided in
           apt-utils).

       o   Sign it. You can do this by running gpg --clearsign -o InRelease
           Release and gpg -abs -o Release.gpg Release.

       o   Publish the key fingerprint, so that your users will know what key
           they need to import in order to authenticate the files in the
           archive. It is best to ship your key in its own keyring package
           like Ubuntu does with ubuntu-keyring to be able to distribute
           updates and key transitions automatically later.

       o   Provide instructions on how to add your archive and key. If your
           users can't acquire your key securely the chain of trust described
           above is broken. How you can help users add your key depends on
           your archive and target audience ranging from having your keyring
           package included in another archive users already have configured
           (like the default repositories of their distribution) to leveraging
           the web of trust.

       Whenever the contents of the archive change (new packages are added or
       removed) the archive maintainer has to follow the first two steps
       outlined above.

SEE ALSO
       apt.conf(5), apt-get(8), sources.list(5), apt-key(8), apt-
       ftparchive(1), debsign(1), debsig-verify(1), gpg(1)

       For more background information you might want to review the Debian
       Security Infrastructure[1] chapter of the Securing Debian Manual (also
       available in the harden-doc package) and the Strong Distribution
       HOWTO[2] by V. Alex Brennen.

BUGS
       APT bug page[3]. If you wish to report a bug in APT, please see
       /usr/share/doc/debian/bug-reporting.txt or the reportbug(1) command.

AUTHOR
       APT was written by the APT team <apt@packages.debian.org>.

MANPAGE AUTHORS
       This man-page is based on the work of Javier Fernandez-Sanguino Pena,
       Isaac Jones, Colin Walters, Florian Weimer and Michael Vogt.

AUTHORS
       Jason Gunthorpe

       APT team

NOTES
        1. Debian Security Infrastructure
           https://www.debian.org/doc/manuals/securing-debian-howto/ch7

        2. Strong Distribution HOWTO
           http://www.cryptnet.net/fdp/crypto/strong_distro.html

        3. APT bug page
           http://bugs.debian.org/src:apt

APT 2.0.10                      06 August 2016                   APT-SECURE(8)