Bring back old semantics to random and randomSeed, add secureRandom (#1710) (#2142)

cores/esp8266/Arduino.h

@@ -271,6 +271,8 @@ void noTone(uint8_t _pin);
 long random(long);
 long random(long, long);
 void randomSeed(unsigned long);
+long secureRandom(long);
+long secureRandom(long, long);
 long map(long, long, long, long, long);
 
 extern "C" void configTime(long timezone, int daylightOffset_sec,

cores/esp8266/WMath.cpp

@@ -28,9 +28,12 @@ extern "C" {
 }
 #include "esp8266_peri.h"
 
+static bool s_randomSeedCalled = false;
+
 void randomSeed(unsigned long seed) {
     if(seed != 0) {
-        srand((seed ^ RANDOM_REG32));
+        srand(seed);
+        s_randomSeedCalled = true;
     }
 }
 
@@ -38,7 +41,9 @@ long random(long howbig) {
     if(howbig == 0) {
         return 0;
     }
-    return (rand() ^ RANDOM_REG32) % howbig;
+    // if randomSeed was called, fall back to software PRNG
+    uint32_t val = (s_randomSeedCalled) ? rand() : RANDOM_REG32;
+    return val % howbig;
 }
 
 long random(long howsmall, long howbig) {
@@ -49,6 +54,21 @@ long random(long howsmall, long howbig) {
     return random(diff) + howsmall;
 }
 
+long secureRandom(long howbig) {
+    if(howbig == 0) {
+        return 0;
+    }
+    return RANDOM_REG32 % howbig;
+}
+
+long secureRandom(long howsmall, long howbig) {
+    if(howsmall >= howbig) {
+        return howsmall;
+    }
+    long diff = howbig - howsmall;
+    return secureRandom(diff) + howsmall;
+}
+
 long map(long x, long in_min, long in_max, long out_min, long out_max) {
     return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
 }

tests/device/test_random/test_random.ino

@@ -0,0 +1,53 @@
+#include <BSTest.h>
+
+BS_ENV_DECLARE();
+
+void setup()
+{
+    Serial.begin(115200);
+    BS_RUN(Serial);
+}
+
+
+TEST_CASE("If randomSeed is not called, random() uses hardware PRNG", "[random]")
+{
+    int32_t data[32];
+    srand(10);
+    for (int i = 0; i < sizeof(data)/sizeof(data[0]); ++i) {
+        data[i] = random(0x7fffffff);
+    }
+    srand(10);
+    for (int i = 0; i < sizeof(data)/sizeof(data[0]); ++i) {
+        CHECK(random(0x7fffffff) != data[i]);
+    }
+}
+
+
+TEST_CASE("If randomSeed is called, we get same random sequence every time", "[random]")
+{
+    const int32_t reference_sequence[] = {
+        2104627054, 2013331137, 258660947, 107061148, 
+        317460219, 663931879, 307161078, 1718702872, 
+        1306951058, 1066376876, 624381721, 850811527, 
+        329784053, 726742932, 182903521, 787925035, 
+        1364123723, 198878220, 1117075042, 1108236242, 
+        1775000610, 500470195, 896676389, 6341838, 
+        785214762, 1084946248, 1601419914, 2058135092, 
+        1671754873, 1952290050, 1572975837, 1596343802, 
+        240941423, 1843946550, 793779187, 441773333, 
+        884819086, 590861527, 1676358848, 2132930493, 
+        969627641, 930717537, 195748182, 2064531490, 
+        1195920216, 347502525, 584628940, 1938341337, 
+        642503024, 915004020, 2034338438, 1690522669, 
+        1805037441, 1904039418, 1491310300, 227517325, 
+        17943876, 570537582, 1409581066, 1819703730, 
+        730240988, 786466794, 1411137128, 1680096093, 
+    };
+    randomSeed(42);
+    for (int i = 0; i < sizeof(reference_sequence)/sizeof(reference_sequence[0]); ++i) {
+        CHECK(random(0x7fffffff) == reference_sequence[i]);
+    }
+}
+
+
+void loop() {}