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https://github.com/kokke/tiny-ECDH-c/issues/25 #26

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https://github.com/kokke/tiny-ECDH-c/issues/25 #26

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8 changes: 8 additions & 0 deletions ecdh.c
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Original file line number Diff line number Diff line change
Expand Up @@ -767,6 +767,14 @@ int ecdh_shared_secret(const uint8_t* private_key, const uint8_t* others_pub, ui
output[i] = others_pub[i];
}

/* Clear bits > CURVE_DEGREE in highest word to satisfy constraint 1 <= exp < n. */
int nbits = bitvec_degree(base_order);

for (int i = (nbits - 1); i < (BITVEC_NWORDS * 32); ++i)
{
bitvec_clr_bit((uint32_t*)private_key, i);
}

/* Multiply other side's public key with own private key */
gf2point_mul((uint32_t*)output,(uint32_t*)(output + BITVEC_NBYTES), (const uint32_t*)private_key);

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