What programming voltage is recommended/required to program the nonvolatile security key in Cyclone VE. I currently set to 3.3V because I thought I saw a 3 to 3.3V requirement for this function somewhere, but I prefer to use 2.5V and get rid of one supply.
There is no limitation on the voltage in order to program the non-volatile security key in Cyclone V E.
However, you will need to ensure that the bitstream is finalized before you program non-volatile security key as everything is not able to redo again.
I would also suggest you to go through the steps at link below for security implementation: