By "keyboard shortcut", I assume you want to perform this using the
keyboard rather than the mouse. Here are the keystrokes you can use,
although I don't know how "short" you'll consider it.
First, highlight the cell(s) whose format you want to copy, then do
Ctrl+C for copy. Then highlight the cell(s) to which you want to copy
the format and do the following "shortcut" keystrokes:
Alt+E, S, t, Enter
(Ignore the dialog boxes that come up on screen as you do this.)