Block cache depending on current node and its last modification time
See my answer to a similar question here: Passing current node ID to the block template

In short, use the plugin context system to get the current node injected. It will automatically ensure that the right cache tags and contexts are added, based on where node is coming from.

Depending on what information you need exactly, you could also consider using the default entity view blocks provided by ctools. That allows you to view the node in a given view mode.