Public bug reported:

I've downloaded DVD ISO images of Lucid from
http://cdimage.ubuntu.com/releases/lucid/release/ and checked their
sha256 hashes with "sha256sum -c SHA256SUMS" - it shows everything is
correct with files.

But when I check the authenticity of SHA256SUMS file with GnuPG it says
that file have BAD signature from "Ubuntu CD Image Automatic Signing
Key".

Am I doing something wrong with checking the signature? Or
SHA256SUMS.gpg file on ubuntu mirrors really did not match the
SHA256SUMS file hosted there? Probably signature files (SHA256SUMS.gpg)
should be updated on Ubuntu mirrors.

I consider this problem to be important because without checking the
signature we can't trust in authenticity of ISO images.

Here is the full output of commands I have executed to check gpg
signatures:


# Check SHA256 hash. Everything is OK with both images
$ sha256sum -c SHA256SUMS
ubuntu-10.04-dvd-amd64.iso: OK
ubuntu-10.04-dvd-i386.iso: OK


# Download latest SHA256SUMS.gpg file
$ wget http://cdimage.ubuntu.com/releases/lucid/release/SHA256SUMS.gpg
--02:41:08--  http://cdimage.ubuntu.com/releases/lucid/release/SHA256SUMS.gpg
           => `SHA256SUMS.gpg'
Resolving cdimage.ubuntu.com... 91.189.92.168
Connecting to cdimage.ubuntu.com|91.189.92.168|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 189 [text/plain]

100%[=============================================================>] 189
--.--K/s

02:41:09 (14.02 MB/s) - `SHA256SUMS.gpg' saved [189/189]


# Time to check it with gpg
$ gpg --verify SHA256SUMS.gpg SHA256SUMS
gpg: Signature made Fri Apr 30 11:03:30 2010 EEST using DSA key ID FBB75451
gpg: Can't check signature: public key not found

# Oops, we don't have a public key of Ubuntu archive.
# Let's download it from the keyserver
$ gpg --keyserver keyserver.ubuntu.com --recv-keys FBB75451
gpg: requesting key FBB75451 from hkp server keyserver.ubuntu.com
gpg: key FBB75451: public key "Ubuntu CD Image Automatic Signing Key 
<[email protected]>" imported
gpg: 3 marginal(s) needed, 1 complete(s) needed, classic trust model
gpg: depth: 0  valid:   1  signed:   1  trust: 0-, 0q, 0n, 0m, 0f, 1u
gpg: depth: 1  valid:   1  signed:   0  trust: 0-, 0q, 0n, 1m, 0f, 0u
gpg: Total number processed: 1
gpg:               imported: 1

# Check the fingerprint of the key
$ gpg --fingerprint  FBB75451
pub   1024D/FBB75451 2004-12-30
      Key fingerprint = C598 6B4F 1257 FFA8 6632  CBA7 4618 1433 FBB7 5451
uid                  Ubuntu CD Image Automatic Signing Key <[email protected]>


# Final check of the signature. It FAILS. :(
$ gpg --verify SHA256SUMS.gpg SHA256SUMS
gpg: Signature made Fri Apr 30 11:03:30 2010 EEST using DSA key ID FBB75451
gpg: BAD signature from "Ubuntu CD Image Automatic Signing Key 
<[email protected]>"

** Affects: ubuntu
     Importance: Undecided
         Status: New

-- 
Bad gpg signature of Lucid DVD iso images
https://bugs.launchpad.net/bugs/576152
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