Improper Protection of Physical Side Channels

As each character of the PIN number is entered, a correct character exhibits one current pulse shape while an incorrect character exhibits a different current pulse shape.

Rather than comparing each character to the correct PIN value as it is entered, the device could accumulate the PIN in a register, and do the comparison all at once at the end. Alternatively, the components for the comparison could be modified so that the current pulse shape is the same regardless of the correctness of the entered character.

The local method of extracting the secret key consists of plugging the key into a USB port and using electromagnetic (EM) sniffing tools and computers.

Several solutions could have been considered by the manufacturer. For example, the manufacturer could shield the circuitry in the key or add randomized delays, indirect calculations with random values involved, or randomly ordered calculations to make extraction much more difficult. The manufacturer could use a combination of these techniques.

... module mod_exp

verilog

if (exponent_reg[0])**

verilog

verilog

... module mod_exp

verilog

if (exponent_reg[0]) begin**

verilog

verilog

mask_reg <= result_next;**

verilog