gpg keys missing

[Florian Idelberger]

without knowing why, i seem to be missing some gpg keys without the 
packages can't be verified so they can't be installled. Where do I get 
them and how to install them? This is what I get (clearing the cache 
didn't help):
[root at localhost sources.list.d]# apt-get -f install gcc-c++
Lese Paketlisten... Fertig
Erzeuge Abhängigkeitsbaum... Fertig
Die folgenden zusätzlichen Pakete werden installiert werden:
   libstdc++-devel (3.3.2-6)
Die folgenden NEUEN Pakete werden installiert werden:
   gcc-c++ (3.3.2-6)
   libstdc++-devel (3.3.2-6)
0 upgraded, 2 newly installed, 0 entfernt und 0 nicht upgegradet.
Muss 0B/3354kB an Archiven holen.
Nach dem Auspacken werden 11,4MB zusätzlicher Plattenplatz benutzt werden.
Wollen Sie fortsetzen? [J/n]
Checking GPG signatures...
Unknown signature 
/var/cache/apt/archives/libstdc++-devel_3.3.2-6_i386.rpm: (SHA1) DSA 
sha1 md5 (GPG) NOT OK (MISSING KEYS: GPG#30c9ecf8)
Unknown signature /var/cache/apt/archives/gcc-c++_3.3.2-6_i386.rpm: 
(SHA1) DSA sha1 md5 (GPG) NOT OK (MISSING KEYS: GPG#30c9ecf8)
E: Error(s) while checking package signatures:
0 unsigned package(s)
2 package(s) with unknown signatures
0 package(s) with illegal/corrupted signatures
[root at localhost sources.list.d]#