Verifying authenticity of Debian images

Official releases of Debian installation and live images come with signed checksum files; look for them alongside the images in the iso-cd, jigdo-dvd, iso-hybrid etc. directories. These files allow you to check that the images you download are correct. First of all, the checksum can be used to check that the images have not been corrupted during download. Secondly, the signatures on the checksum files allow you to confirm that the images are the ones created and released by Debian, and have not been tampered with.

To validate the contents of an image file, be sure to use the appropriate checksum tool. Cryptographically strong checksum algorithms (SHA256 and SHA512) are available for every releases; you should use the matching tools sha256sum or sha512sum to work with these.

To ensure that the checksums files themselves are correct, use GnuPG to verify them against the accompanying signature files (e.g. SHA512SUMS.sign). The keys used for these signatures are all in the Debian GPG keyring and the best way to check them is to use that keyring to validate via the web of trust. To make life easier for people who don't have ready access to an existing Debian machine, here are details of the keys that have been used to sign releases in recent years, and links to download the public keys directly:

pub   rsa4096/988021A964E6EA7D 2009-10-03
      Key fingerprint = 1046 0DAD 7616 5AD8 1FBC  0CE9 9880 21A9 64E6 EA7D
uid                  Debian CD signing key <debian-cd@lists.debian.org>

pub   rsa4096/DA87E80D6294BE9B 2011-01-05 [SC]
      Key fingerprint = DF9B 9C49 EAA9 2984 3258  9D76 DA87 E80D 6294 BE9B
uid                  Debian CD signing key <debian-cd@lists.debian.org>

pub   rsa4096/42468F4009EA8AC3 2014-04-15 [SC]
      Key fingerprint = F41D 3034 2F35 4669 5F65  C669 4246 8F40 09EA 8AC3
uid                  Debian Testing CDs Automatic Signing Key <debian-cd@lists.debian.org>