Make bits2int reduce mod n (#53)
diff --git a/uECC.c b/uECC.c
index e8ecaf2..c7d759a 100644
--- a/uECC.c
+++ b/uECC.c
@@ -407,7 +407,7 @@
const uECC_word_t *mod,
wordcount_t num_words) {
uECC_word_t carry = uECC_vli_add(result, left, right, num_words);
- if (carry || uECC_vli_cmp_unsafe(result, mod, num_words) >= 0) {
+ if (carry || uECC_vli_cmp_unsafe(mod, result, num_words) != 1) {
/* result > mod (result = mod + remainder), so subtract mod to get remainder. */
uECC_vli_sub(result, result, mod, num_words);
}
@@ -1023,19 +1023,24 @@
if (bits_size > num_n_bytes) {
bits_size = num_n_bytes;
}
+ uECC_vli_clear(native, num_n_words);
uECC_vli_bytesToNative(native, bits, bits_size, curve);
if (bits_size * 8 <= (unsigned)curve->num_n_bits) {
return;
}
int shift = bits_size * 8 - curve->num_n_bits;
uECC_word_t carry = 0;
- uECC_word_t *end = native;
- native += num_n_words;
- while (native-- > end) {
- uECC_word_t temp = *native;
- *native = (temp >> shift) | carry;
+ uECC_word_t *ptr = native + num_n_words;
+ while (ptr-- > native) {
+ uECC_word_t temp = *ptr;
+ *ptr = (temp >> shift) | carry;
carry = temp << (uECC_WORD_BITS - shift);
}
+
+ /* Reduce mod curve_n */
+ if (uECC_vli_cmp_unsafe(curve->n, native, num_n_words) != 1) {
+ uECC_vli_sub(native, native, curve->n, num_n_words);
+ }
}
static int uECC_sign_with_k(const uint8_t *private_key,
