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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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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
consists of an interrupt handler that is supposed to be called every millisecond
or so. The handler waits for a random number of cpu ticks that is a sample of so
called floating mean distribution. That means that the number is the sum of two
numbers generated uniformly at random in the interval [0, 255]. The first number
is generated freshly for each call of the handler, the other number is supposed
to be refreshed when the device performs an operation that leaks the current
state of the execution flow, such as sending or receiving an usb packet.
Random delay interrupts (RDI) is a contermeasure against side channel attacks.
It consists of an interrupt handler that is supposed to be called every
millisecond or so. The handler waits for a random number of cpu ticks that is a
sample of so called floating mean distribution. That means that the number is
the sum of two numbers generated uniformly at random in the interval [0, 255].
The first number is generated freshly for each call of the handler, the other
number is supposed to be refreshed when the device performs an operation that
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
Christophe Clavier, Jean-Sebastien Coron, Nora Dabbous and Efficient Use of