Issue
I ran apt-get update and got the following warning message:
The following signatures were invalid: EXPKEYSIG ED75B5A4483DA07C Andrey Smirnov me@smira.ru W: GPG error: http://repo.aptly.info squeeze InRelease: The following signatures were invalid: EXPKEYSIG ED75B5A4483DA07C Andrey Smirnov me@smira.ru
Solution
For my case, GPG key that I used to access http://repo.aptly.info has expired. I went to their website at https://www.aptly.info/download/ and got the latest key.
wget -qO - https://www.aptly.info/pubkey.txt | apt-key add -
About the author
Xuan Ngo is the founder of OpenWritings.net. He currently lives in Montreal, Canada. He loves to write about programming and open source subjects.