This question already has an answer here:
I have followed the instructions from various posts at the forum and I when I execute in the terminal
sudo dd if=/path/to/downloaded.img of=/dev/rdiskN bs=1m
then it requires the password but instead it does not let me type the password. If i press enter then the same thing until I repeat it three times which will require me to execute the above command again. Anyone knows why and how to solve it?