Abstract: A system for determining which key of a key-pad device is activated by an algorithm that employs the same number of steps to make the determination regardless of which key is pressed. In one embodiment, the algorithm first determines if more than one key is pressed in more than one column. The algorithm then determines which key has been pressed by adding key values associated with each key on a row-by-row basis. Once the algorithm calculates the added value, it then determines whether the added key value exceeds a predetermined value to determine if more than one key has been pressed in the rows. If the added value does not exceed the predetermine value, then the added value is subtracted from another predetermined value to give the key value that is transferred from the device.

Abstract: A system for determining which key of a key-pad device is activated that prevents an unauthorized person from determining secret information therefrom. The key-pad device determines which key is activated by an algorithm that employs the same number of steps to make the determination regardless of which key is pressed. In one embodiment, the algorithm first determines if more than one key is pressed in more than one column. The algorithm then determines which key has been pressed by adding key values associated with each key on a row-by-row basis. Once the algorithm calculates the added value, it then determines whether the added key value exceeds a predetermined value to determine if more than one key has been pressed in the rows. If the added value does not exceed the predetermine value, then the added value is subtracted from another predetermined value to give the key value that is transferred from the device.

Abstract: Method and apparatus for managing sensitive data. In one embodiment, sensitive data are managed in a circuit arrangement that includes a processor, a RAM, a register, a security circuit, and a power supply. The power supply is arranged to provide power from a first power source when power is available from the first source and from a second power source when power is unavailable from the first source. The processor initially stores the sensitive data in the RAM while operating with power from the first source. Upon loss of power from the first source, the power supply provides power from the second source, and the processor copies the sensitive data from the slow discharging RAM to the register and erases the sensitive data from the RAM. If the second power source is removed, the processor clears the sensitive data from the register. When the security circuit detects an attack on the circuit arrangement, the processor erases the sensitive data from the RAM and from the register.