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sys/puf_sram: counter based reseed after soft reset

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This commit is contained in:
PeterKietzmann 2020-01-15 17:19:54 +01:00
parent 8d16ccb96a
commit 9dd3219c3f
2 changed files with 19 additions and 0 deletions
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7
sys/include/puf_sram.h
View File

@ -89,6 +89,13 @@ extern uint32_t puf_sram_seed;
*/
extern uint32_t puf_sram_state;
/**
* @brief Counter variable allocated in puf_sram.c. It is incremented
during each soft reset when no new PUF measurement was taken
and it gets reset to zero after a power cycle was detected.
*/
extern uint32_t puf_sram_softreset_cnt;
/**
* @brief checks source of reboot by @p puf_sram_softreset and conditionally
calls @p puf_sram_generate

12
sys/puf_sram/puf_sram.c
View File

@ -24,6 +24,9 @@ PUF_SRAM_ATTRIBUTES uint32_t puf_sram_seed;
/* Allocation of the PUF seed state */
PUF_SRAM_ATTRIBUTES uint32_t puf_sram_state;
/* Allocation of the PUF soft reset conter*/
PUF_SRAM_ATTRIBUTES uint32_t puf_sram_softreset_cnt;
/* Allocation of the memory marker */
PUF_SRAM_ATTRIBUTES uint32_t puf_sram_marker;
@ -42,6 +45,8 @@ void puf_sram_generate(const uint8_t *ram, size_t len)
puf_sram_marker = PUF_SRAM_MARKER;
/* setting state to 0 means seed was generated from SRAM pattern */
puf_sram_state = 0;
/* reset counter of detected soft resets */
puf_sram_softreset_cnt = 0;
}
bool puf_sram_softreset(void)
@ -51,5 +56,12 @@ bool puf_sram_softreset(void)
return 0;
}
puf_sram_state = 1;
/* increment number of detected soft resets */
puf_sram_softreset_cnt++;
/* generate alterntive seed value */
puf_sram_seed ^= puf_sram_softreset_cnt;
puf_sram_seed = dek_hash((uint8_t *)&puf_sram_seed, sizeof(puf_sram_seed));
return 1;
}