Dear reader, about to state the obvious here, as we are required to do so. We are not out to screw you. We have no interest in your personal information.
Permissions
For Android 4.4 and above, permission is required to read from and write to the call log. This is to allow you to pick numbers from your call log to block and to allow Blokka to delete blocked calls from the call log.
The permissions for Android 4.3 or earlier, state that Blokka can read from and write to your contacts. Blokka doesn't read from or write to your contacts. That permission is required because you can't specify permission to read the call log on those versions and have to get permission to read the contacts instead.
You also have to grant permission for Blokka to read the device state and identity. This is just so Blokka knows when there's an incoming call.
The permissions also state that Blokka can directly call phone numbers. It doesn't do this but it needs that level of permission to end a call, which it does do.
Charles Sweeney - Blokka developer - June 2017