How to solve "signatures couldn't be verified" when running "sudo apt-get update"?

Hi i got this error while running the sudo apt-get update command on my Ubuntu machine :(

Error:

Fetched 308B in 1s (158B/s)
Reading package lists... Done
W: GPG error: intrepid Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 5A9BF3BB4E5E17B5
W: You may want to run apt-get update to correct these problems

2 Answers

You need to download the gpg key:

gpg --keyserver keyserver.ubuntu.com --recv 4E5E17B5
gpg --export --armor 4E5E17B5 | sudo apt-key add -

See

In ubuntu 9.10, if repositories are added using the command add-apt-repository, the keys are automatically imported. This way, you don't get this error/warning.