Merge pull request #13137 from PeterKietzmann/pr_puf_opt_softreset

sys/puf_sram: counter based seed after soft reset

sys/include/puf_sram.h

@@ -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

sys/puf_sram/puf_sram.c

@@ -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;
 }

tests/puf_sram/Makefile

@@ -3,5 +3,6 @@ BOARD ?= nucleo-f411re
 include ../Makefile.tests_common
 
 USEMODULE += puf_sram
+DISABLE_MODULE += test_utils_interactive_sync
 
 include $(RIOTBASE)/Makefile.include