Provided by: apt_1.0.1ubuntu2.24_amd64 
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
archives. This ensures that packages in the archive can't be modified by people who have no access to the
Release file signing key.
If a package comes from a archive without a signature, or with a signature that apt does not have a key
for, that package is considered untrusted, and installing it will result in a big warning. apt-get will
currently only warn for unsigned archives; future releases might force all sources to be verified before
downloading packages from them.
The package frontends apt-get(8), aptitude(8) and synaptic(8) support this new authentication feature.
TRUSTED ARCHIVES
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 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
the Debian Maintainers keyring (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.
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:
• 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).
• 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 Debian 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.
USER CONFIGURATION
apt-key is the program that manages the list of keys used by apt. It can be used to add or remove keys,
although an installation of this release will automatically contain the default Debian archive signing
keys used in the Debian package repositories.
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.
ARCHIVE CONFIGURATION
If you want to provide archive signatures in an archive under your maintenance you have to:
• Create a toplevel Release file, if it does not exist already. You can do this by running
apt-ftparchive release (provided in apt-utils).
• Sign it. You can do this by running gpg --clearsign -o InRelease Release and gpg -abs -o Release.gpg
Release.
• Publish the key fingerprint, that way your users will know what key they need to import in order to
authenticate the files in the archive.
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 (available also 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 Fernández-Sanguino Peña, Isaac Jones, Colin Walters, Florian
Weimer and Michael Vogt.
AUTHORS
Jason Gunthorpe
APT team
NOTES
1. Debian Security Infrastructure
http://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 1.0.1ubuntu2.24 09 June 2012 APT-SECURE(8)