Command "sudo apt-get update" do not work and return error message

[iyasin]

hi all,
i am using ubuntu 13.04(i have upgraded it from u12.10), now i have a problem with it. when i enter the command "sudo apt-get update" in terminal, it get below error

E: GPG error: http://extras.ubuntu.com raring Release: The following signatures were invalid: NODATA 1 NODATA 2

i followed below instructions but that error occupied for me too:

sudo apt-get clean
sudo mv /var/lib/apt/lists /tmp
sudo mkdir -p /var/lib/apt/lists/partial
sudo apt-get clean
sudo apt-get update

how can i solve this problem?
tnx.

[ranger1021994]

Try this way :
Install Y-PPA Manager
Go to Advanced tab
Select fix GPG BADSIG error
The above commands do the same i guess but give this method a shot

[iyasin]

Try this way :
Install Y-PPA Manager
Go to Advanced tab
Select fix GPG BADSIG error
The above commands do the same i guess but give this method a shot

i have installed it, and do fix GPG BADSIG error option but this error returned to me

W: A error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://extras.ubuntu.com raring Release: The following signatures were invalid: NODATA 1 NODATA 2

W: Failed to fetch http://extras.ubuntu.com/ubuntu/dists/raring/Release  

W: Some index files failed to download. They have been ignored, or old ones used instead.

[oldos2er]

iyasin, see post #6 in this thread . I'm not sure why suggestions are for BADSIG errors when you're seeing a NODATA error.

[iyasin]

iyasin, see post #6 in this thread . I'm not sure why suggestions are for BADSIG errors when you're seeing a NODATA error.

tnx, i try it