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kaleb-himes merged 1 commit into from
Jun 17, 2025
Merged

Entropy - fix off by ones in continuous testing #8820

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49 changes: 34 additions & 15 deletions wolfcrypt/src/random.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1124,6 +1124,16 @@ static word64 Entropy_GetSample(void)
word64 now;
word64 ret;

#ifdef HAVE_FIPS
/* First sample must be disregard when in FIPS. */
if (entropy_last_time == 0) {
/* Get sample which triggers CAST in FIPS mode. */
Entropy_MemUse();
/* Start entropy time after CASTs. */
entropy_last_time = Entropy_TimeHiRes();
}
#endif

/* Use memory such that it will take an unpredictable amount of time. */
Entropy_MemUse();

Expand Down Expand Up @@ -1225,6 +1235,7 @@ static int Entropy_HealthTest_Repetition(byte noise)
if (!rep_have_prev) {
rep_prev_noise = noise;
rep_have_prev = 1;
rep_cnt = 1;
}
/* Check whether this sample matches last. */
else if (noise == rep_prev_noise) {
Expand Down Expand Up @@ -1258,7 +1269,7 @@ static int Entropy_HealthTest_Repetition(byte noise)
/* SP800-90b 4.4.2 - Adaptive Proportion Test
* Note 10
* C = 1 + CRITBINOM(W, power(2,( -H)),1-alpha)
* alpa = 2^-30 = POWER(2,-30), H = 1, W = 512
* alpha = 2^-30 = POWER(2,-30), H = 1, W = 512
* C = 1 + CRITBINOM(512, 0.5, 1-POWER(2,-30)) = 1 + 324 = 325
*/
#define PROP_CUTOFF 325
Expand Down Expand Up @@ -1308,8 +1319,9 @@ static int Entropy_HealthTest_Proportion(byte noise)
{
int ret = 0;

/* Need at least 512-1 samples to test with. */
if (prop_total < PROP_WINDOW_SIZE - 1) {
/* Need minimum samples in queue to test with - keep adding while we have
* less. */
if (prop_total < PROP_CUTOFF - 1) {
/* Store sample at last position in circular queue. */
prop_samples[prop_last++] = noise;
/* Update count of seen value based on new sample. */
Expand All @@ -1318,27 +1330,32 @@ static int Entropy_HealthTest_Proportion(byte noise)
prop_total++;
}
else {
/* Get first value in queue - value to test. */
byte val = (byte)prop_samples[prop_first];
/* Store new sample in queue. */
/* We have at least a minimum set of samples in queue. */
/* Store new sample at end of queue. */
prop_samples[prop_last] = noise;
/* Update first index now that we have removed in from the queue. */
prop_first = (prop_first + 1) % PROP_WINDOW_SIZE;
/* Update last index now that we have added new sample to queue. */
prop_last = (prop_last + 1) % PROP_WINDOW_SIZE;
/* Removed sample from queue - remove count. */
prop_cnt[val]--;
/* Added sample to queue - add count. */
prop_cnt[noise]++;
/* Check whether removed value has too many repetitions in queue. */
if (prop_cnt[val] >= PROP_CUTOFF) {

/* Check whether first value has too many repetitions in queue. */
if (prop_cnt[noise] >= PROP_CUTOFF) {
#ifdef WOLFSSL_DEBUG_ENTROPY_MEMUSE
fprintf(stderr, "PROPORTION FAILED: %d %d\n", val, prop_cnt[val]);
fprintf(stderr, "PROPORTION FAILED: %d %d\n", val, prop_cnt[noise]);
#endif
Entropy_HealthTest_Proportion_Reset();
/* Error code returned. */
ret = ENTROPY_APT_E;
}
else if (prop_total == PROP_WINDOW_SIZE) {
/* Return to 511 samples in queue. */
/* Get first value in queue - value to test. */
byte val = (byte)prop_samples[prop_first];
/* Update first index to remove first sample from the queue. */
prop_first = (prop_first + 1) % PROP_WINDOW_SIZE;
/* Removed first sample from queue - remove count. */
prop_cnt[val]--;
}
}

return ret;
Expand Down Expand Up @@ -1371,6 +1388,10 @@ static int Entropy_HealthTest_Startup(void)
#ifdef WOLFSSL_DEBUG_ENTROPY_MEMUSE
fprintf(stderr, "STARTUP HEALTH TEST\n");
#endif

/* Reset cached values before testing. */
Entropy_HealthTest_Reset();

/* Fill initial sample buffer with noise. */
Entropy_GetNoise(initial, ENTROPY_INITIAL_COUNT);
/* Health check initial noise. */
Expand Down Expand Up @@ -1537,8 +1558,6 @@ int wc_Entropy_OnDemandTest(void)
}

if (ret == 0) {
/* Reset health test state for startup test. */
Entropy_HealthTest_Reset();
/* Perform startup tests. */
ret = Entropy_HealthTest_Startup();
}
Expand Down