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style(core): trezorhal/random_delays.c

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Martin Milata 2021-07-07 13:08:21 +02:00 committed by matejcik
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commit f06a57237b
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core/embed/trezorhal/random_delays.c
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@ -18,14 +18,15 @@
*/ */
/* /*
Random delay interrupts (RDI) is a contermeasure against side channel attacks. It Random delay interrupts (RDI) is a contermeasure against side channel attacks.
consists of an interrupt handler that is supposed to be called every millisecond It consists of an interrupt handler that is supposed to be called every
or so. The handler waits for a random number of cpu ticks that is a sample of so millisecond or so. The handler waits for a random number of cpu ticks that is a
called floating mean distribution. That means that the number is the sum of two sample of so called floating mean distribution. That means that the number is
numbers generated uniformly at random in the interval [0, 255]. The first number the sum of two numbers generated uniformly at random in the interval [0, 255].
is generated freshly for each call of the handler, the other number is supposed The first number is generated freshly for each call of the handler, the other
to be refreshed when the device performs an operation that leaks the current number is supposed to be refreshed when the device performs an operation that
state of the execution flow, such as sending or receiving an usb packet. leaks the current state of the execution flow, such as sending or receiving an
usb packet.
See Differential Power Analysis in the Presence of Hardware Countermeasures by See Differential Power Analysis in the Presence of Hardware Countermeasures by
Christophe Clavier, Jean-Sebastien Coron, Nora Dabbous and Efficient Use of Christophe Clavier, Jean-Sebastien Coron, Nora Dabbous and Efficient Use of