title: R Backports and Invalid Signature
body: <p>I run debian stable (bullseye) and I use the official R backports.
  See</p>
  <p><a href="https://cloud.r-project.org/bin/linux/debian/" rel="noreferrer">https://cloud.r-project.org/bin/linux/debian/</a></p>
  <p>I added a line to mu repositories</p>
  <pre><code>$ cat /etc/apt/sources.list | grep r-project
  deb http://cloud.r-project.org/bin/linux/debian bullseye-cran40/
  </code></pre>
  <p>And everything has been good until today.
  Now, when I update, I get an error about the signature of the R repository when I run sudo apt update, see</p>
  <pre><code>W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://cloud.r-project.org/bin/linux/debian bullseye-cran40/ InRelease: The following signatures were invalid: EXPKEYSIG FCAE2A0E115C3D8A Johannes Ranke (Wissenschaftlicher Berater) &lt;johannes.ranke@jrwb.de&gt;
  W: Failed to fetch http://cloud.r-project.org/bin/linux/debian/bullseye-cran40/InRelease  The following signatures were invalid: EXPKEYSIG FCAE2A0E115C3D8A Johannes Ranke (Wissenschaftlicher Berater) &lt;johannes.ranke@jrwb.de&gt;
  W: Some index files failed to download. They have been ignored, or old ones used instead.
  </code></pre>
  <p>The signature has always been working until now.
  I reimported it following the instructions here</p>
  <p><a href="https://cloud.r-project.org/bin/linux/debian/#administration-and-maintenance" rel="noreferrer">https://cloud.r-project.org/bin/linux/debian/#administration-and-maintenance</a></p>
  <p>which I paste below</p>
  <pre><code>You can fetch and import the current key using
  
  apt-key adv --keyserver keyserver.ubuntu.com --recv-key 'E19F5F87128899B192B1A2C2AD5F960A256A04AF'
  
  Note that you need to add sudo if you are not running this as root.
  
  If this fails, it may be due to a firewall blocking port 11371. In this case, you can search for 0xE19F5F87128899B192B1A2C2AD5F960A256A04AF at https://keyserver.ubuntu.com, and copy the key block shown when klicking on the link in the line starting with pub into a plain text file, named, for instance, jranke.asc which you add to apt with (sudo) apt-key add jranke.asc.
  </code></pre>
  <p>but it does not work.
  I import the signature, but when I update I am always told it is not valid.
  Anyone else is experiencing the same? Any ideas?
  Thanks!</p>