Debian signature key changing
The Debian project has announced that the signature keys for the unstable (Sid) and testing (Squeeze) branches of Debian will change at the beginning of July. Debian has, therefore, already started to distribute new keys via the debian-archive-keyring package. Users should make sure that at least version 2009.01.31 is installed. From mid June, packages should only be signed using the new keys.
The automatic update function also provides new signature packages with new keys for Etch users. According to Debian, Lenny already contains new keys and requires no update. Debian regularly updates its keys for security reasons (every three years).