Q:

Google Chrome PPA upgrade invalid signature

When running:
sudo apt-get update && sudo apt-get dist-upgrade

I got this output:
Ign http://security.ubuntu.com utopic-security InRelease
Ign http://gb.archive.ubuntu.com utopic InRelease                              
Ign http://extras.ubuntu.com utopic InRelease                                  
Get:1 http://security.ubuntu.com utopic-security Release.gpg [933 B]           
Ign http://dl.google.com stable InRelease                                      
Ign http://gb.archive.ubuntu.com utopic-updates InRelease            
Get:2 http://extras.ubuntu.com utopic Release.gpg [72 B]                       
Get:3 http://security.ubuntu.com utopic-security Release [62.0 kB]             
Ign http://gb.archive.ubuntu.com utopic-backports InRelease                    
Get:4 http://dl.google.com stable Release.gpg [198 B]                          
Hit http://extras.ubuntu.com utopic Release                                    
Hit http://gb.archive.ubuntu.com utopic Release.gpg                            
Get:5 http://dl.google.com stable Release [1,347 B]                            
Err http://dl.google.com stable Release                                        

Get:6 http://gb.archive.ubuntu.com utopic-updates Release.gpg [933 B]          
Hit http://extras.ubuntu.com utopic/main Sources                         
Hit http://gb.archive.ubuntu.com utopic-backports Release.gpg
Get:7 http://security.ubuntu.com utopic-security/main Sources [44.6 kB]
Hit http://gb.archive.ubuntu.com utopic Release                                
Hit http://extras.ubuntu.com utopic/main amd64 Packages                        
Get:8 http://gb.archive.ubuntu.com utopic-updates Release [62.0 kB]            
Hit http://extras.ubuntu.com utopic/main i386 Packages                         
Get:9 http://security.ubuntu.com utopic-security/restricted Sources [2,107 B]  
Get:10 http://security.ubuntu.com utopic-security/universe Sources [8,053 B]   
Get:11 http://security.ubuntu.com utopic-security/multiverse Sources [1,951 B] 
Hit http://gb.archive.ubuntu.com utopic-backports Release                      
Get:12 http://security.ubuntu.com utopic-security/main amd64 Packages [129 kB] 
Hit http://gb.archive.ubuntu.com utopic/main Sources                           
Hit http://gb.archive.ubuntu.com utopic/restricted Sources                     
Hit http://gb.archive.ubuntu.com utopic/universe Sources                       
Hit http://gb.archive.ubuntu.com utopic/multiverse Sources              
Get:13 http://security.ubuntu.com utopic-security/restricted amd64 Packages [8,496 B]
Hit http://gb.archive.ubuntu.com utopic/main amd64 Packages                    
Get:14 http://security.ubuntu.com utopic-security/universe amd64 Packages [54.4 kB]
Hit http://gb.archive.ubuntu.com utopic/restricted amd64 Packages              
Ign http://extras.ubuntu.com utopic/main Translation-en_GB                     
Hit http://gb.archive.ubuntu.com utopic/universe amd64 Packages                
Ign http://extras.ubuntu.com utopic/main Translation-en                        
Get:15 http://security.ubuntu.com utopic-security/multiverse amd64 Packages [4,139 B]
Hit http://gb.archive.ubuntu.com utopic/multiverse amd64 Packages              
Hit http://gb.archive.ubuntu.com utopic/main i386 Packages                     
Get:16 http://security.ubuntu.com utopic-security/main i386 Packages [128 kB]
Hit http://gb.archive.ubuntu.com utopic/restricted i386 Packages       
Hit http://gb.archive.ubuntu.com utopic/universe i386 Packages                 
Get:17 http://security.ubuntu.com utopic-security/restricted i386 Packages [8,438 B]
Hit http://gb.archive.ubuntu.com utopic/multiverse i386 Packages               
Get:18 http://security.ubuntu.com utopic-security/universe i386 Packages [54.4 kB]
Hit http://gb.archive.ubuntu.com utopic/main Translation-en_GB                 
Hit http://gb.archive.ubuntu.com utopic/main Translation-en                    
Get:19 http://security.ubuntu.com utopic-security/multiverse i386 Packages [4,325 B]
Hit http://gb.archive.ubuntu.com utopic/multiverse Translation-en_GB           
Hit http://security.ubuntu.com utopic-security/main Translation-en
Hit http://gb.archive.ubuntu.com utopic/multiverse Translation-en
Hit http://security.ubuntu.com utopic-security/multiverse Translation-en
Hit http://gb.archive.ubuntu.com utopic/restricted Translation-en_GB
Hit http://security.ubuntu.com utopic-security/restricted Translation-en
Hit http://gb.archive.ubuntu.com utopic/restricted Translation-en
Hit http://gb.archive.ubuntu.com utopic/universe Translation-en_GB
Hit http://gb.archive.ubuntu.com utopic/universe Translation-en
Get:20 http://gb.archive.ubuntu.com utopic-updates/main Sources [81.0 kB]
Hit http://security.ubuntu.com utopic-security/universe Translation-en 
Get:21 http://gb.archive.ubuntu.com utopic-updates/restricted Sources [2,107 B]
Get:22 http://gb.archive.ubuntu.com utopic-updates/universe Sources [19.9 kB]
Get:23 http://gb.archive.ubuntu.com utopic-updates/multiverse Sources [1,951 B]
Get:24 http://gb.archive.ubuntu.com utopic-updates/main amd64 Packages [208 kB]
Get:25 http://gb.archive.ubuntu.com utopic-updates/restricted amd64 Packages [8,496 B]
Get:26 http://gb.archive.ubuntu.com utopic-updates/universe amd64 Packages [81.3 kB]
Get:27 http://gb.archive.ubuntu.com utopic-updates/multiverse amd64 Packages [4,139 B]
Get:28 http://gb.archive.ubuntu.com utopic-updates/main i386 Packages [207 kB] 
Get:29 http://gb.archive.ubuntu.com utopic-updates/restricted i386 Packages [8,438 B]
Get:30 http://gb.archive.ubuntu.com utopic-updates/universe i386 Packages [81.3 kB]
Get:31 http://gb.archive.ubuntu.com utopic-updates/multiverse i386 Packages [4,325 B]
Hit http://gb.archive.ubuntu.com utopic-updates/main Translation-en               
Hit http://gb.archive.ubuntu.com utopic-updates/multiverse Translation-en
Hit http://gb.archive.ubuntu.com utopic-updates/restricted Translation-en
Hit http://gb.archive.ubuntu.com utopic-updates/universe Translation-en
Hit http://gb.archive.ubuntu.com utopic-backports/main Sources
Hit http://gb.archive.ubuntu.com utopic-backports/restricted Sources
Hit http://gb.archive.ubuntu.com utopic-backports/multiverse Sources
Hit http://gb.archive.ubuntu.com utopic-backports/universe Sources
Hit http://gb.archive.ubuntu.com utopic-backports/main amd64 Packages
Hit http://gb.archive.ubuntu.com utopic-backports/restricted amd64 Packages
Hit http://gb.archive.ubuntu.com utopic-backports/multiverse amd64 Packages
Hit http://gb.archive.ubuntu.com utopic-backports/universe amd64 Packages
Hit http://gb.archive.ubuntu.com utopic-backports/main i386 Packages
Hit http://gb.archive.ubuntu.com utopic-backports/restricted i386 Packages
Hit http://gb.archive.ubuntu.com utopic-backports/multiverse i386 Packages
Hit http://gb.archive.ubuntu.com utopic-backports/universe i386 Packages
Hit http://gb.archive.ubuntu.com utopic-backports/main Translation-en
Hit http://gb.archive.ubuntu.com utopic-backports/multiverse Translation-en
Hit http://gb.archive.ubuntu.com utopic-backports/restricted Translation-en
Hit http://gb.archive.ubuntu.com utopic-backports/universe Translation-en
Fetched 1,283 kB in 6s (207 kB/s)                                                                                                              
Reading package lists... Done
W: An error occurred during the signature verification.  The repository is not updated and the previous index files will be used.  GPG error: http://dl.google.com stable Release: The following signatures were invalid: BADSIG A040830F7FAC5991 Google, Inc. Linux Package Signing Key <linux-packages-keymaster@google.com>

W: Failed to fetch http://dl.google.com/linux/chrome/deb/dists/stable/Release  

W: Some index files failed to download.  They have been ignored, or old ones used instead. 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Calculating upgrade... Done
0 to upgrade, 0 to newly install, 0 to remove and 0 not to upgrade. 

Is this bit:
W: An error occurred during the signature verification.  The repository is not updated and the previous index files will be used.  GPG error: http://dl.google.com stable Release: The following signatures were invalid: BADSIG A040830F7FAC5991 Google, Inc. Linux Package Signing Key <linux-packages-keymaster@google.com>

W: Failed to fetch http://dl.google.com/linux/chrome/deb/dists/stable/Release  

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

Anything to worry about?  I ran the commands again and now it says:
Ign http://extras.ubuntu.com utopic InRelease
Ign http://dl.google.com stable InRelease                                                        
Ign http://gb.archive.ubuntu.com utopic InRelease                                                 
Hit http://extras.ubuntu.com utopic Release.gpg                                                   
Ign http://gb.archive.ubuntu.com utopic-updates InRelease                                         
Get:1 http://dl.google.com stable Release.gpg [198 B]                                                                   
Hit http://extras.ubuntu.com utopic Release                                                                                        
Ign http://gb.archive.ubuntu.com utopic-backports InRelease                                       
Hit http://gb.archive.ubuntu.com utopic Release.gpg                                         
Get:2 http://dl.google.com stable Release [1,347 B]                                         
Get:3 http://gb.archive.ubuntu.com utopic-updates Release.gpg [933 B]  
Hit http://gb.archive.ubuntu.com utopic-backports Release.gpg          
Ign http://security.ubuntu.com utopic-security InRelease               
Hit http://gb.archive.ubuntu.com utopic Release                        
Get:4 http://gb.archive.ubuntu.com utopic-updates Release [62.0 kB]                                              
Hit http://extras.ubuntu.com utopic/main Sources                                                                         
Get:5 http://security.ubuntu.com utopic-security Release.gpg [933 B]                                                     
Get:6 http://dl.google.com stable/main amd64 Packages [1,193 B]                                      
Hit http://extras.ubuntu.com utopic/main amd64 Packages                                                                                     
Hit http://gb.archive.ubuntu.com utopic-backports Release                                   
Hit http://extras.ubuntu.com utopic/main i386 Packages                                                             
Get:7 http://dl.google.com stable/main i386 Packages [1,176 B]                              
Get:8 http://security.ubuntu.com utopic-security Release [62.0 kB]                                         
Ign http://extras.ubuntu.com utopic/main Translation-en_GB                                           
Ign http://extras.ubuntu.com utopic/main Translation-en                        
Ign http://dl.google.com stable/main Translation-en_GB                         
Ign http://dl.google.com stable/main Translation-en                      
Get:9 http://security.ubuntu.com utopic-security/main Sources [44.6 kB]
Get:10 http://security.ubuntu.com utopic-security/restricted Sources [2,107 B]
Get:11 http://gb.archive.ubuntu.com utopic-updates/main Sources [81.0 kB]
Get:12 http://security.ubuntu.com utopic-security/universe Sources [8,053 B]
Get:13 http://gb.archive.ubuntu.com utopic-updates/restricted Sources [2,107 B]  
Get:14 http://security.ubuntu.com utopic-security/multiverse Sources [1,951 B]    
Get:15 http://gb.archive.ubuntu.com utopic-updates/universe Sources [19.9 kB]     
Get:16 http://gb.archive.ubuntu.com utopic-updates/multiverse Sources [1,951 B]
Get:17 http://gb.archive.ubuntu.com utopic-updates/main amd64 Packages [208 kB]
Get:18 http://security.ubuntu.com utopic-security/main amd64 Packages [129 kB]
Get:19 http://gb.archive.ubuntu.com utopic-updates/restricted amd64 Packages [8,496 B]
Get:20 http://security.ubuntu.com utopic-security/restricted amd64 Packages [8,496 B]
Get:21 http://gb.archive.ubuntu.com utopic-updates/universe amd64 Packages [81.3 kB]
Get:22 http://security.ubuntu.com utopic-security/universe amd64 Packages [54.4 kB]
Get:23 http://gb.archive.ubuntu.com utopic-updates/multiverse amd64 Packages [4,139 B]         
Get:24 http://gb.archive.ubuntu.com utopic-updates/main i386 Packages [207 kB]      
Get:25 http://security.ubuntu.com utopic-security/multiverse amd64 Packages [4,139 B]
Get:26 http://security.ubuntu.com utopic-security/main i386 Packages [128 kB]     
Get:27 http://gb.archive.ubuntu.com utopic-updates/restricted i386 Packages [8,438 B]
Get:28 http://gb.archive.ubuntu.com utopic-updates/universe i386 Packages [81.3 kB]           
Get:29 http://gb.archive.ubuntu.com utopic-updates/multiverse i386 Packages [4,325 B]        
Get:30 http://security.ubuntu.com utopic-security/restricted i386 Packages [8,438 B]
Get:31 http://gb.archive.ubuntu.com utopic-backports/main Sources [765 B]          
Hit http://gb.archive.ubuntu.com utopic-backports/restricted Sources    
Hit http://gb.archive.ubuntu.com utopic-backports/multiverse Sources    
Get:32 http://security.ubuntu.com utopic-security/universe i386 Packages [54.4 kB]
Get:33 http://gb.archive.ubuntu.com utopic-backports/universe Sources [9,218 B]
Get:34 http://gb.archive.ubuntu.com utopic-backports/main amd64 Packages [570 B]  
Hit http://gb.archive.ubuntu.com utopic-backports/restricted amd64 Packages      
Hit http://gb.archive.ubuntu.com utopic-backports/multiverse amd64 Packages
Get:35 http://security.ubuntu.com utopic-security/multiverse i386 Packages [4,325 B]
Get:36 http://gb.archive.ubuntu.com utopic-backports/universe amd64 Packages [10.6 kB]
Get:37 http://gb.archive.ubuntu.com utopic-backports/main i386 Packages [574 B]
Hit http://gb.archive.ubuntu.com utopic-backports/restricted i386 Packages
Hit http://gb.archive.ubuntu.com utopic-backports/multiverse i386 Packages
Get:38 http://gb.archive.ubuntu.com utopic-backports/universe i386 Packages [10.6 kB]
Hit http://gb.archive.ubuntu.com utopic-backports/multiverse Translation-en
Hit http://gb.archive.ubuntu.com utopic-backports/restricted Translation-en
Hit http://gb.archive.ubuntu.com utopic/main Sources
Hit http://gb.archive.ubuntu.com utopic/restricted Sources    
Hit http://gb.archive.ubuntu.com utopic/universe Sources      
Hit http://gb.archive.ubuntu.com utopic/multiverse Sources
Hit http://gb.archive.ubuntu.com utopic/main amd64 Packages
Hit http://gb.archive.ubuntu.com utopic/restricted amd64 Packages
Hit http://gb.archive.ubuntu.com utopic/universe amd64 Packages
Hit http://gb.archive.ubuntu.com utopic/multiverse amd64 Packages
Hit http://gb.archive.ubuntu.com utopic/main i386 Packages
Hit http://gb.archive.ubuntu.com utopic/restricted i386 Packages   
Hit http://gb.archive.ubuntu.com utopic/universe i386 Packages     
Hit http://security.ubuntu.com utopic-security/main Translation-en 
Hit http://gb.archive.ubuntu.com utopic/multiverse i386 Packages   
Hit http://gb.archive.ubuntu.com utopic/main Translation-en_GB     
Hit http://gb.archive.ubuntu.com utopic/main Translation-en        
Hit http://gb.archive.ubuntu.com utopic/multiverse Translation-en_GB
Hit http://security.ubuntu.com utopic-security/multiverse Translation-en
Hit http://gb.archive.ubuntu.com utopic/multiverse Translation-en
Hit http://gb.archive.ubuntu.com utopic/restricted Translation-en_GB
Hit http://gb.archive.ubuntu.com utopic/restricted Translation-en
Hit http://gb.archive.ubuntu.com utopic/universe Translation-en_GB
Hit http://security.ubuntu.com utopic-security/restricted Translation-en
Hit http://gb.archive.ubuntu.com utopic/universe Translation-en
Hit http://gb.archive.ubuntu.com utopic-updates/main Translation-en
Hit http://gb.archive.ubuntu.com utopic-updates/multiverse Translation-en
Hit http://gb.archive.ubuntu.com utopic-updates/restricted Translation-en
Hit http://security.ubuntu.com utopic-security/universe Translation-en
Hit http://gb.archive.ubuntu.com utopic-updates/universe Translation-en
Hit http://gb.archive.ubuntu.com utopic-backports/main Translation-en
Hit http://gb.archive.ubuntu.com utopic-backports/universe Translation-en
Fetched 1,316 kB in 11s (115 kB/s)                                                                                                             
Reading package lists... Done
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Calculating upgrade... Done
The following packages will be upgraded:
  google-chrome-stable
1 to upgrade, 0 to newly install, 0 to remove and 0 not to upgrade. 
Need to get 48.5 MB of archives. 
After this operation, 4,096 B of additional disk space will be used. 
Do you want to continue? [ Y/n] 

So what does this mean and should I trust this upgrade?  This upgrade is from a PPA that Google Chrome added when I installed it from the official Google page for it. 
Here is more information about that PPA:

OS Information:
Description:    Ubuntu 14.10
Release:    14.10

A:

Open a terminal and enter the following:
wget -q -O - https://dl-ssl.google.com/linux/linux_signing_key.pub | sudo apt-key add -

That will import Google's updated GPG Key. 
You should be able to update the system without any errors. 
Source: Google Linux Repositories

A:

This site has the only solution that worked for me on 64-bit Ubuntu 14.04 LTS:
http://www.omgubuntu.co.uk/2016/03/fix-failed-to-fetch-google-chrome-apt-error-ubuntu
(Here's a summary.  Please see the site for more detail)

Edit google-chrome.list (assuming you’re on the Stable Channel, if not, see the featured comment on the site):
sudo gedit /etc/apt/sources.list.d/google-chrome.list

In the text file that opens edit the file so that the line reads:
deb [arch=amd64] http://dl.google.com/linux/chrome/deb/ stable main

Try update again
sudo apt-get update

A:

This will work better than these solutions:
apt-key list google

You will see this on this list, take not [E] means expired and look at the last 7FAC 5991
pub   dsa1024 2007-03-08 [SC]
      4CCA 1EAF 950C EE4A B839  76DC A040 830F 7FAC 5991
uid           [ unknown] Google, Inc. Linux Package Signing Key <linux-packages-keymaster@google.com>
sub   elg2048 2007-03-08 [E]

pub   rsa4096 2016-04-12 [SC]
      EB4C 1BFD 4F04 2F6D DDCC  EC91 7721 F63B D38B 4796
uid           [ unknown] Google Inc. (Linux Packages Signing Authority) <linux-packages-keymaster@google.com>
sub   rsa4096 2016-04-12 [S] [expires: 2019-04-12]

You will do now:
sudo apt-key del 7FAC5991

Then you will do these commands:
sudo apt-get clean
cd /var/lib/apt
sudo mv lists lists.old
sudo mkdir -p lists/partial
sudo apt-get clean
sudo apt-get update

And after that's done you will do this to install keyring from another keyserver:
wget -q -O - https://dl.google.com/linux/linux_signing_key.pub | sudo apt-key add -

And then you do:
sudo apt-get update
sudo apt-get dist-upgrade

Now you are all set. :)