Difference between revisions of "DeveloperWiki:Package signing"

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(Ideas)
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==== Cons ====
 
==== Cons ====
 
* Space greedy (2 files for 1 package)
 
* Space greedy (2 files for 1 package)
 
=pacman internals=
 
==Package file format==
 
* packages are {{filename|.tar.xz}} by default, but some are {{filename|.tar.gz}}. See [http://www.archlinux.org/news/switching-to-xz-compression-for-new-packages/ this news article] for further details. Extract with {{codeline|tar -xJvf pkgname.pkg.tar.xz}}
 
* within the archive, the location of a file gives the installation location (relative to /): extracting a package to / installs it
 
* there are two hidden files in the archive's / directory:
 
** {{filename|.PKGINFO}} is a text file with package metadata. It is generated using information in the {{filename|PKGBUILD}}. It is used to generate the {{filename|desc}} file, which goes in the sync database
 
** {{filename|.INSTALL}} is an optional shell script that can define functions that are called after install, upgrade, or remove operations. It is placed in the same directory as the {{filename|PKGBUILD}} when building (e.g. {{filename|pkgname.install}}) and is named inside the {{filename|PKGBUILD}} with {{Codeline|<nowiki>install=pkgname.install</nowiki>}}. It is stored in the local database after the package is installed
 
* installed packages are cached in {{filename|/var/cache/pacman/pkg/}}
 
* further information at [[Creating Packages]]
 
==Database file format==
 
* there are two database types: the local database (stored at {{filename|/var/lib/pacman/local/}}) and the sync databases (stored in {{filename|/var/lib/pacman/sync/}})
 
** there is one sync database per repository
 
*** the sync databases are .tar.gz format but have a .db file extension
 
*** each sync database has a directory for each package. Each directory contains the files {{filename|depends}} and {{filename|desc}}, which give dependencies and metadata, respectively
 
*** the {{filename|desc}} file contains the MD5sum and optionally the signature
 
** the local database has a directory for each installed package, which contains the files {{filename|desc}}, a rearranged version of the sync db's {{filename|desc}} that omits some information like the MD5sum; {{filename|files}}, which lists the files comprising the package; and optionally {{filename|install}}, a copy of {{filename|.INSTALL}}
 
  
 
=Links=
 
=Links=

Revision as of 16:54, 14 June 2011

This page will act as a brain dump and collaborative design document for implementation of package signing in pacman.

Currently implemented signing functionality in pacman and associated tools

  • Template:Codeline can sign a package
  • Template:Codeline can add said signature to the database and sign the database
  • Template:Codeline exists for the sake of managing keys, but there is missing functionality
  • Template:Codeline can verify package signatures from repo databases, detached (.sig) package signatures, and signatures of the repos themselves (still some work to do)

How Arch will implement package signing

  • Packages will be signed using Template:Codeline. This creates a detached binary signature (.sig).
  • The signed package will be added to the repository, and a detached signature of the repository will be generated, using Template:Codeline. The command line options indicate that the signature of the old database will be verified, and that the new database will be signed. Independently of these options, Template:Codeline will detect the detached signature, convert it via base64 to ASCII, and add it to the repository.
  • Template:Codeline will download both the databases and the database signatures and verify the databases upon database sync and each time the database is opened. When a package is loaded, its signature will be checked whether that comes from a repo database or a standalone .sig file.

Course of action

Requirements

These are the changes that need to be made before Arch can implement package signing.

arch-keyring package

Some package will be created that contains all necessary keys for an Arch user to validate package signatures.

Key Policy

The DeveloperWiki page for key creation must be finalized. Several developers and now Kerrick are working on this; feel free to contribute.

Key creation, submission and verification

Solely the responsibility of the developers. This page gives the current progress.

Testing

pactests must be written for all signing functionality. This is a big issue; if you would like to contribute, this is a good place to do so.

Documentation

Documentation for the new features must be reviewed and finalized.

Additional Features

These are important but non-essential features that should be added soon after package signing is implemented. Work on these issues can start now, but priority should be given to the "requirements" above.

Package validation without root privileges

Currently, pacman's GnuPG home directory (aka gpgdir, typically /etc/pacman.d/gnupg/) must be locked in order to check a package's signature. Only root can perform this locking, so either locking must be disabled for read-only accesses, or the directory must be copied/linked to a writable location when a user is performing package verification.

Timeline for increasing security

A timeline for transitioning between some unsigned packages and a fully-signed set of packages must be made. This is the responsibility of the developers.

Allan's TODO list

Allan has a TODO list with further needed features at User:Allan/Package Signing.

How signing is implemented in other distributions

Frugalware

Frugalware uses a fork of pacman which implements package signing (verify)

Gnuffy

Arch based distro gnuffy uses signed packages with their custom package manager Spaceman modeled on pacman.

Debian

Binary packages (.deb)

To sum up, the GPG signature is included in the .deb.

Details:

Regular non signed binary packages are "ar" archives of at least 3 files:

  • data.tar.gz (files to be installed)
  • control.tar.gz (package metadata)
  • debian-binary (contains the version of the deb format)

Signed packages also have a _gpgorigin file at the root of the .deb that is a "gpg -abs" of the concatenation of the 3 laters (as explained here):

cat debian-binary control.tar.gz data.tar.gz > /tmp/combined-contents
gpg -abs -o _gpgorigin /tmp/combined-contents (-a "Create ASCII armored output" ; -b "detach signature" ; -s "sign")

Source packages

Original files are provided on the repo like this acpid_2.0.4.orig.tar.gz with diff if necessary (acpid_2.0.4-1.diff.gz). A description file containing MD5sums of the orig.tar.gz and diff.gz is written and signed using GPG and uploaded along these.

Gentoo

Redhat/Fedora/CentOS

  • Signature type: GPG
  • Stored: in the RPM

A RPM package is a tarball of installed files to which is added a header made up of metadata (name of package, version, ...). This metadata can contain a GPG signature of the tarball. See the file format specification for details.

NB: packages built for the RedHat Network are signed with the RedHat official key(s) but technically a RPM can be signed using any other key (one can even add another signature to the RPM)

To check a package correction, one must first import the signer's key first: Example for RedHat

rpm --import /usr/share/doc/rpm-4.1/RPM-GPG-KEY

And can then check signature manually:

$ rpm -K openldap-clients-2.3.43-4.x86_64.rpm 
  openldap-clients-2.3.43-4.x86_64.rpm: sha1 md5 OK

And even fully check the package (MD5):

$ rpm -Kv openldap-clients-2.3.43-4.x86_64.rpm 
  openldap-clients-2.3.43-4.x86_64.rpm:
     SHA1 header hash: OK (65999383ad859be0ce337aee4c1f6bd049ebe4a0)
     MD5 sum: OK (4be23a341d23b794d08fbee35c459c83)

Option --nogpg prevents rpm from checking GPG signatures

Pros

  • Enable Official Distribution package signature but also enables personal and multiple signatures

Cons

  • Implies complicated package format with header containing signature of an inner tarball (not very KISS)
  • Space greedy on repos

Suse

Slackware

Ubuntu

For each package, a small description file containing the SHA sum of the package is created. That file is then signed using gpg (.dsc) and uploaded within the same folder as the package:

gpg --clearsign description_of_package

See result for acpid in Ubuntu

Cons

  • Space greedy (2 files for 1 package)

Links

Bug reports

  1. Bugreport Signed packages

Blogs

  1. Geoffrey carriers blog
  2. Attack on package managers
  3. Attack faq

Mailing list discussions and patches

  1. Add Keyring option in alpm/pacman
  2. Package signing again
  3. PATCH (newgpg) Let pacman specify GnuPG's home directory.
  4. Dan's pacman tree build&test
  5. GPG work
  6. GPG signature option in makepkg patch
  7. GPG signature support for makepkg
  8. GPG signature option in makepkg, adapted to Dan McGee's suggestions patch
  9. GPG verification patch
  10. GPGSIG in repo-add patch
  11. Signing by default
  12. Package Database signing
  13. Pointless to use non-md5 for makepkg INTEGRITY_CHECK
  14. Can we trust our mirrors
  15. Multiple/Shared Architectures

Forum discussions

  1. Pacman vulnerable to MITM attacks?
  2. Arch approach to security
  3. Pacman Veanurability
  4. Package signing
  5. pacman vulnerabilities