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Restore tinycrypt implementation of regularize_k()

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The fix is required to prevent array overrun

Signed-off-by: Shelly Liberman <shelly.liberman@arm.com>
This commit is contained in:
Shelly Liberman 2020-10-25 18:48:06 +02:00
parent 8472bc76c6
commit 8176022b22
1 changed files with 11 additions and 1 deletions
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12
tinycrypt/ecc.c
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@ -1610,10 +1610,20 @@ static void EccPoint_mult(uECC_word_t * result, const uECC_word_t * point,
static uECC_word_t regularize_k(const uECC_word_t * const k, uECC_word_t *k0,
uECC_word_t *k1)
{
wordcount_t num_n_words = NUM_ECC_WORDS;
bitcount_t num_n_bits = NUM_ECC_BITS;
/* With our constant NUM_ECC_BITS and NUM_ECC_WORDS the
* check (num_n_bits < ((bitcount_t)num_n_words * uECC_WORD_SIZE * 8) always would have "false" result (256 < 256),
* therefore Coverity warning may be detected. Removing of this line without changing the entire check will cause to
* array overrun.
* The entire check is not changed on purpose to be aligned with original tinycrypt
* implementation and to allow upstreaming to other curves if required.
* Coverity specific annotation may be added to silence warning if exists.
*/
uECC_word_t carry = uECC_vli_add(k0, k, curve_n) ||
uECC_vli_testBit(k0, num_n_bits);
(num_n_bits < ((bitcount_t)num_n_words * uECC_WORD_SIZE * 8) &&
uECC_vli_testBit(k0, num_n_bits));
uECC_vli_add(k1, k0, curve_n);