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Make bits2int reduce mod n (#53)

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This commit is contained in:
Ken MacKay
2015-10-12 21:29:57 -07:00
parent 0283b542ef
commit 6826dd4789
1 changed files with 11 additions and 6 deletions
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uECC.c
+11 -6
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@@ -407,7 +407,7 @@ uECC_VLI_API void uECC_vli_modAdd(uECC_word_t *result,
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 @@ static void bits2int(uECC_word_t *native,
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,