The key used to sign portage snapshots, 0x7DDAD20D, has not been signed by the release engineering team, so its not possible for users to determine if this key belongs to gentoo or not. If the releng team signs this key with the release key, then users can apply the same amount of trust to this key. $ gpg --list-sigs 0x7DDAD20D pub 1024D/0x7DDAD20D 2005-11-23 [expires: 2007-11-23] uid Gentoo Portage Snapshot Signing Key (Automated Signing Key) sig 3 0x7DDAD20D 2005-11-23 Gentoo Portage Snapshot Signing Key (Automated Signing Key)
The keys are now explicitly documented here: http://www.gentoo.org/proj/en/releng/