Authenticating 'focal.tar.gz' against 'focal.tar.gz.gpg' fails [closed]

Question

When trying to perform a do-release-upgrade to upgrade from Ubuntu 18.04 to 20.04 I am getting the below error

Checking for a new Ubuntu release
Get:1 Upgrade tool signature [1,554 B]                                                                                                 
Get:2 Upgrade tool [1,342 kB]                                                                                                          
Fetched 1,343 kB in 0s (0 B/s)                                                                                                         
authenticate 'focal.tar.gz' against 'focal.tar.gz.gpg' 
Authentication failed
Authenticating the upgrade failed. 
There may be a problem with the network or with the server.

FYI: I already tried sudo apt-get install --reinstall ubuntu-keyring.

Answer 1

Now I'm able to upgrade to ubuntu 20 after replacing below contents in /etc/apt/sources.list

deb http://in.archive.ubuntu.com/ubuntu/ focal main restricted universe multiverse
deb-src http://in.archive.ubuntu.com/ubuntu/ focal main restricted universe multiverse

deb http://in.archive.ubuntu.com/ubuntu/ focal-updates main restricted universe multiverse
deb-src http://in.archive.ubuntu.com/ubuntu/ focal-updates main restricted universe multiverse

deb http://in.archive.ubuntu.com/ubuntu/ focal-security main restricted universe multiverse
deb-src http://in.archive.ubuntu.com/ubuntu/ focal-security main restricted universe multiverse

deb http://in.archive.ubuntu.com/ubuntu/ focal-backports main restricted universe multiverse
deb-src http://in.archive.ubuntu.com/ubuntu/ focal-backports main restricted universe multiverse

deb http://archive.canonical.com/ubuntu focal partner
deb-src http://archive.canonical.com/ubuntu focal partner