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6.6. Sjekking av pakkeautensitet

Sikkerheten er veldig viktig for Falcot Corps administratorer. Følgelig må de sørge for at de bare installerer pakker som er garantert å komme fra Debian uten å være tuklet med underveis. En som vil knekke en datamaskin (en cracker) kan prøve å legge ondsinnet kode til en ellers lovlig pakke. En slik pakke, hvis den er installert, kunne gjøre noe knekkeren utviklet det til å gjøre, inkludert for eksempel å avdekke passord eller konfidensiell informasjon. For å omgå denne risikoen gir Debian nye installasjoner en forsegling som det ikke kan kludres med, for å garantere at en pakke virkelig kommer fra dens offisielle vedlikeholder, og ikke er endret av en tredjepart.
The seal works with a chain of cryptographic hashes and a signature and is explained in detail in apt-secure(8). Starting with Debian 10 Buster the signed file is the InRelease file, provided by the Debian mirrors. There is also a legacy file called Release. Both contain a list of the Packages files (including their compressed forms, Packages.gz and Packages.xz, and the incremental versions), along with their SHA256 hashes, which ensures that the files haven't been tampered with. These Packages files contain a list of the Debian packages available on the mirror, along with their hashes, which ensures in turn that the contents of the packages themselves haven't been altered either. The difference between InRelease and Release is that the former is cryptographically signed in-line, whereas the latter provides a detached signature in the form of the file Release.gpg.
APT needs a set of trusted GnuPG public keys to verify signatures in the InRelease and Release.gpg files available on the mirrors. It gets them from files in /etc/apt/trusted.gpg.d/ and from the /etc/apt/trusted.gpg keyring (managed by the apt-key command). The official Debian keys are provided and kept up-to-date by the debian-archive-keyring package which puts them in /etc/apt/trusted.gpg.d/:
# ls /etc/apt/trusted.gpg.d/
debian-archive-bullseye-automatic.gpg
debian-archive-bullseye-security-automatic.gpg
debian-archive-bullseye-stable.gpg
debian-archive-buster-automatic.gpg
debian-archive-buster-security-automatic.gpg
debian-archive-buster-stable.gpg
debian-archive-stretch-automatic.gpg
debian-archive-stretch-security-automatic.gpg
debian-archive-stretch-stable.gpg
Once the appropriate keys are in the keyring, APT will check the signatures before any risky operation, so that frontends will display a warning if asked to install a package whose authenticity can't be ascertained.
Merk at binærpakker vanligvis ikke er signerte. Integriteten for en pakke kan bekreftes ved å kontrollere sjekksummen mot en tiltrodd (og mulig signert) sjekksumskilde.