altos: Use standard FIPS testing for chaoskey

[fw/altos] / src / drivers / ao_trng_send.c

diff --git a/src/drivers/ao_trng_send.c b/src/drivers/ao_trng_send.c
index 00efa8d9e336ff5787a507c76b65e1af56152000..85034efd767f7337ebbabbff75a428fccd6b8e73 100644 (file)
--- a/src/drivers/ao_trng_send.c
+++ b/src/drivers/ao_trng_send.c
@@ -97,18 +97,7 @@ ao_trng_send_raw(void)
 
 #endif
 
-/* Make sure there's at least 8 bits of variance in the samples */
-#define MIN_VARIANCE           (128 * 128)
-
-/* Make sure the signal is spread around a bit */
-#define MAX_VARIANCE           (512 * 512)
-
-#define ADD_STATS(value) do {                  \
-               sum += (value);                 \
-               sum2 += (value) * (value);      \
-       } while(0)
-
-#define VARIANCE(n)    ((sum2 - (sum / (n) * sum)) / (n))
+static uint32_t        previous[AO_USB_IN_SIZE / sizeof (uint16_t)];
 
 static int
 ao_trng_get_cooked(uint16_t *buf)
@@ -116,29 +105,24 @@ ao_trng_get_cooked(uint16_t *buf)
        uint16_t        i;
        uint16_t        t;
        uint32_t        *rnd = (uint32_t *) ao_adc_ring;
-       int32_t         sum, sum2, var;
+       uint8_t         mismatch = 0;
 
-       sum = sum2 = 0;
        t = ao_adc_get(AO_USB_IN_SIZE) >> 1;            /* one 16-bit value per output byte */
        for (i = 0; i < AO_USB_IN_SIZE / sizeof (uint16_t); i++) {
                uint32_t        v;
-               uint16_t        v1, v2;
 
                /* Fetch two values in one operation */
                v = rnd[t];
+               if (v != previous[i]) {
+                       mismatch = 1;
+                       previous[i] = v;
+               }
                t = (t + 1) & ((AO_ADC_RING_SIZE >> 1) - 1);
 
                *buf++ = ao_crc_in_32_out_16(v);
-
-               v1 = v;
-               v2 = v >> 16;
-
-               ADD_STATS(v1);
-               ADD_STATS(v2);
        }
        ao_adc_ack(AO_USB_IN_SIZE);
-       var = VARIANCE(2 * AO_USB_IN_SIZE / sizeof (uint16_t));
-       return var >= MIN_VARIANCE && var <= MAX_VARIANCE;
+       return mismatch;
 }
 
 #define AO_TRNG_START_WAIT     1024