"License server response has not passed data integrity check: Invalid signature format" error on product activation via a license server is caused by an outdated version of the license server used to obtain the ticket.
Starting with the 2018.2.1 release of JetBrains IDEs (released in Q3 2018), products no longer obtain license tickets from the old versions of JetBrains license servers (versions prior to #16429 which was released on March 19, 2018).
To find the version number of the license server you are using, look in the license server log or in the web interface.
Please note that if you are using a product version older than 2018.2.1, it is still possible to use an old license server.
What do I need to do?
Please update the license server to the latest version by following the upgrade procedure described in the documentation.
Your JetBrains Account profile should be authorized to use a JetBrains license server. Please contact JetBrains Sales if you need any assistance with such authorization. If you are not sure whether you have obtained such permission before, we recommend that you reach out to us anyway so that we can minimize any possible downtime of the license server while the authorization is being granted.
Should you have any questions or requests about old license servers, please contact us by completing the form on the deprecation notice page for quick assistance or contact License Server support via firstname.lastname@example.org.