How to enter CWM recovery on an encrypted Galaxy S3?
How to get into Recovery Mode
Unplug the USB cable.
Shut down the phone.
Hold down the 'HOME' + 'VOLUME UP' buttons and press the 'POWER' button for about 5 seconds to enter Recovery Mode.

How to get into Download Mode (eg: for Odin)
Unplug the USB cable.
Shut down the phone.
Hold down the 'HOME' + 'VOLUME DOWN' buttons and press the 'POWER' button for about 2 seconds until a WARNING! Screen appears. Press the 'VOLUME UP' button to enter Download Mode.
To get out of Download Mode, simply press and hold the power button until the phone restarts.