During a recent apt-get update of one of our systems, we encountered an error with the R1Soft repository for CDP:
W: GPG error: http://repo.r1soft.com stable Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 1BF3530AA40384ED
It appears that R1Soft started using a new key which they publish. In order to get this repository working again, you must update to use the new key. Use the following commands to import the new key:
apt-key add r1soft.asc
The key (pun intendned) of this post is to remind myself of the URL of the public key block.