The script initializes the image from /dev/zero, which means that an attacker can tell which blocks of the filesystem image are data and which are empty. Unles

The script initializes the image from /dev/zero, which means that an attacker can tell which blocks of the filesystem image are data and which are empty. Unless you really can't afford to wait the minute or so for it to finish, use /dev/urandom - or /dev/random, if you've got access to sufficient entropy (did you pay extra for a hardware random number generator?).