hash&salt code simplified

include/cyclic.h

@@ -10,6 +10,7 @@
 #include "display.h"
 #include "sds011read.h"
 #include "sdcard.h"
+#include "macsniff.h"
 
 extern Ticker cyclicTimer;
 

include/macsniff.h

@@ -14,7 +14,7 @@
 #include "corona.h"
 #endif
 
-uint16_t get_salt(void);
+uint32_t renew_salt(void);
 uint64_t macConvert(uint8_t *paddr);
 esp_err_t macQueueInit(void);
 void mac_process(void *pvParameters);

src/cyclic.cpp

@@ -97,7 +97,6 @@ void doHousekeeping() {
              "free heap = %d bytes)",
              ESP.getMinFreeHeap(), ESP.getFreeHeap());
     reset_counters(); // clear macs container and reset all counters
-    get_salt();       // get new salt for salting hashes
 
     if (ESP.getMinFreeHeap() <= MEM_LOW) // check again
       do_reset(true);                    // memory leak, reset device
@@ -108,7 +107,6 @@ void doHousekeeping() {
   if (ESP.getMinFreePsram() <= MEM_LOW) {
     ESP_LOGI(TAG, "PSRAM full, counter cleared");
     reset_counters(); // clear macs container and reset all counters
-    get_salt();       // get new salt for salting hashes
 
     if (ESP.getMinFreePsram() <= MEM_LOW) // check again
       do_reset(true);                     // memory leak, reset device
@@ -140,6 +138,7 @@ void reset_counters() {
   macs.clear(); // clear all macs container
   macs_wifi = 0;
   macs_ble = 0;
+  renew_salt(); // get new salt
 #ifdef HAS_DISPLAY
   dp_plotCurve(0, true);
 #endif

src/macsniff.cpp

@@ -9,10 +9,11 @@ static const char TAG[] = __FILE__;
 QueueHandle_t MacQueue;
 TaskHandle_t macProcessTask;
 
-uint16_t salt = 0;
+static uint32_t salt = renew_salt();
 
-uint16_t get_salt(void) {
-  salt = (uint16_t)random(65536); // get new 16bit random for salting hashes
+uint32_t renew_salt(void) {
+  salt = esp_random();
+  ESP_LOGV(TAG, "new salt = %04X", salt);
   return salt;
 }
 
@@ -101,9 +102,6 @@ void IRAM_ATTR mac_add(uint8_t *paddr, int8_t rssi, snifftype_t sniff_type) {
 
 uint16_t mac_analyze(MacBuffer_t MacBuffer) {
 
-  if (salt == 0) // ensure we have salt (appears after radio is turned on)
-    return 0;
-
   if ((cfg.rssilimit) &&
       (MacBuffer.rssi < cfg.rssilimit)) { // rssi is negative value
     ESP_LOGI(TAG, "%s RSSI %d -> ignoring (limit: %d)",
@@ -126,8 +124,7 @@ uint16_t mac_analyze(MacBuffer_t MacBuffer) {
     }
   };
 
-  char buff[10]; // temporary buffer for printf
-  uint32_t *mac; // temporary buffer for shortened MAC
+  uint32_t *mac; // pointer to shortened 4 byte MAC
 
   // only last 3 MAC Address bytes are used for MAC address anonymization
   // but since it's uint32 we take 4 bytes to avoid 1st value to be 0.
@@ -138,10 +135,14 @@ uint16_t mac_analyze(MacBuffer_t MacBuffer) {
   // and increment counter on display
   // https://en.wikipedia.org/wiki/MAC_Address_Anonymization
 
-  snprintf(buff, sizeof(buff), "%08X",
-           *mac + (uint32_t)salt); // convert unsigned 32-bit salted MAC
-                                   // to 8 digit hex string
-  uint16_t hashedmac = hash(&buff[3], 5); // hash MAC 8 digit -> 5 digit
+  // reversed 4 byte MAC added to current salt
+  const uint32_t saltedmac = *mac + salt;
+
+  // hashed 4 byte MAC
+  // to save RAM, we use only lower 2 bytes of hash, since collisions don't
+  // matter in our use case
+  const uint16_t hashedmac = hash((const char *)&saltedmac, 4);
+
   auto newmac = macs.insert(hashedmac); // add hashed MAC, if new unique
   bool added =
       newmac.second ? true : false; // true if hashed MAC is unique in container
@@ -183,7 +184,8 @@ uint16_t mac_analyze(MacBuffer_t MacBuffer) {
 
   // Log scan result
   ESP_LOGV(TAG,
-           "%s %s RSSI %ddBi -> salted MAC %s -> Hash %04X -> WiFi:%d  "
+           "%s %s RSSI %ddBi -> MAC %0x:%0x:%0x:%0x:%0x:%0x -> salted %04X"
+           " -> hashed %04X -> WiFi:%d  "
            "BLTH:%d "
 #if (COUNT_ENS)
            "(CWA:%d)"
@@ -191,7 +193,9 @@ uint16_t mac_analyze(MacBuffer_t MacBuffer) {
            "-> %d Bytes left",
            added ? "new  " : "known",
            MacBuffer.sniff_type == MAC_SNIFF_WIFI ? "WiFi" : "BLTH",
-           MacBuffer.rssi, buff, hashedmac, macs_wifi, macs_ble,
+           MacBuffer.rssi, MacBuffer.mac[0], MacBuffer.mac[1], MacBuffer.mac[2],
+           MacBuffer.mac[3], MacBuffer.mac[4], MacBuffer.mac[5], saltedmac,
+           hashedmac, macs_wifi, macs_ble,
 #if (COUNT_ENS)
            cwa_report(),
 #endif

src/main.cpp

@@ -428,7 +428,7 @@ void setup() {
   // initialize salt value using esp_random() called by random() in
   // arduino-esp32 core. Note: do this *after* wifi has started, since
   // function gets it's seed from RF noise
-  get_salt(); // get new 16bit for salting hashes
+  reset_counters();
 
   // start state machine
   ESP_LOGI(TAG, "Starting Interrupt Handler...");

src/rcommand.cpp

@@ -18,7 +18,6 @@ void set_reset(uint8_t val[]) {
   case 1: // reset MAC counter
     ESP_LOGI(TAG, "Remote command: reset MAC counter");
     reset_counters(); // clear macs
-    get_salt();       // get new salt
     break;
   case 2: // reset device to factory settings
     ESP_LOGI(TAG, "Remote command: reset device to factory settings");
@@ -119,7 +118,6 @@ void set_countmode(uint8_t val[]) {
     return;
   }
   reset_counters(); // clear macs
-  get_salt();       // get new salt
 }
 
 void set_screensaver(uint8_t val[]) {

src/senddata.cpp

@@ -115,7 +115,6 @@ void sendData() {
       // clear counter if not in cumulative counter mode
       if (cfg.countermode != 1) {
         reset_counters(); // clear macs container and reset all counters
-        get_salt();       // get new salt for salting hashes
         ESP_LOGI(TAG, "Counter cleared");
       }
 #ifdef HAS_DISPLAY