Geometric leaks are memory leaks caused by current
flow from bit-lines to the ground via activated ROM cells.
Since input data corresponds to address in the ROM, secret
keys can easily be discovered during memory leaks by the
attacker.
To reduce geometric leaks, new ROM structures are
needed. For example, a ROM consists of NMOS transistor
pairs allows the charge flows from the bit-lines to the
ground. Nakai proposed a ROM circuit with the bit-line
fixed to ground and a sense amplifier circuit for the output;
thus, geometric leaks can be hidden