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Adds random nonce (r) option to hf mf sim.

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This makes the PM3 generate pseudo-random nonces rather than sequential
nonces, to make it act a bit more like a "real" MFC card.  A reader would
otherwise be able to detect the PM3 probing based on the predictable nonces
and throw different authentication challenges (or refuse to authenticate at
all).

The code includes an implementation of a rand-like function (prand), similar
to the one from libc, which is seeded automatically based on the time it
takes between the PM3 starting up and the first call to the RNG.

This isn't cryptographically random, but should be "good enough" to be able
to evade basic detection.
This commit is contained in:
Michael Farrell 2017-01-26 18:16:10 +11:00
commit f9c1dcd9f6
5 changed files with 42 additions and 2 deletions
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16
armsrc/util.c
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@ -431,3 +431,19 @@ uint32_t RAMFUNC GetCountSspClk(){
}
}
static uint64_t next_random = 1;
/* Generates a (non-cryptographically secure) 32-bit random number.
*
* We don't have an implementation of the "rand" function or a clock to seed it
* with, so we just call GetTickCount the first time to seed ourselves.
*/
uint32_t prand() {
if (next_random == 1) {
next_random = GetTickCount();
}
next_random = next_random * 6364136223846793005 + 1;
return (uint32_t)(next_random >> 32) % 0xffffffff;
}