apt-getの鍵問題。

apt-get update
Get:1 http://ftp.jp.debian.org lenny Release.gpg [386B]
Ign http://ftp.jp.debian.org lenny/main Translation-en_US
Get:2 http://ftp.jp.debian.org lenny Release [63.2kB]
Get:3 http://ftp.jp.debian.org lenny/main Packages [5295kB]
Get:4 http://ftp.jp.debian.org lenny/main Sources [2304kB]
Get:5 http://security.debian.org etch/updates Release.gpg [189B]
Ign http://security.debian.org etch/updates/main Translation-en_US
Ign http://security.debian.org etch/updates/contrib Translation-en_US
Get:6 http://security.debian.org etch/updates Release [37.6kB]
Ign http://security.debian.org etch/updates/main Packages/DiffIndex
Ign http://security.debian.org etch/updates/contrib Packages/DiffIndex
Ign http://security.debian.org etch/updates/main Sources/DiffIndex
Ign http://security.debian.org etch/updates/contrib Sources/DiffIndex
Get:7 http://security.debian.org etch/updates/main Packages [315kB]
Hit http://security.debian.org etch/updates/contrib Packages
Get:8 http://security.debian.org etch/updates/main Sources [50.4kB]
Hit http://security.debian.org etch/updates/contrib Sources
Fetched 8065kB in 9s (862kB/s)
Reading package lists... Done
W: There is no public key available for the following key IDs:
4D270D06F42584E6
W: You may want to run apt-get update to correct these problems

上記のように鍵が・・・と言われる事がある。
その時はすかさず、
apt-get install debian-archive-keyring
これで問題解消。