//does a * P where a is a scalar and P is an arbitrary point
void scalarmultKey(key & aP, const key &P, const key &a) {
ge_p3 A;
ge_p2 R;
CHECK_AND_ASSERT_THROW_MES(ge_frombytes_vartime(&A, P.bytes) == 0, "ge_frombytes_vartime failed at "+boost::lexical_cast<std::string>(__LINE__));
ge_scalarmult(&R, a.bytes, &A);
ge_tobytes(aP.bytes, &R);
}
void crypto_ops::generate_key_image(const public_key &pub, const secret_key &sec, key_image &image) {
ge_p3 point;
ge_p2 point2;
assert(sc_check(&sec) == 0);
hash_to_ec(pub, point);
ge_scalarmult(&point2, &sec, &point);
ge_tobytes(&image, &point2);
}
//Computes aH where H= toPoint(cn_fast_hash(G)), G the basepoint
key scalarmultH(const key & a) {
ge_p3 A;
ge_p2 R;
CHECK_AND_ASSERT_THROW_MES(ge_frombytes_vartime(&A, H.bytes) == 0, "ge_frombytes_vartime failed at "+boost::lexical_cast<std::string>(__LINE__));
ge_scalarmult(&R, a.bytes, &A);
key aP;
ge_tobytes(aP.bytes, &R);
return aP;
}
bool crypto_ops::generate_key_derivation(const public_key &key1, const secret_key &key2, key_derivation &derivation) {
ge_p3 point;
ge_p2 point2;
ge_p1p1 point3;
assert(sc_check(&key2) == 0);
if (ge_frombytes_vartime(&point, &key1) != 0) {
return false;
}
ge_scalarmult(&point2, &key2, &point);
ge_mul8(&point3, &point2);
ge_p1p1_to_p2(&point2, &point3);
ge_tobytes(&derivation, &point2);
return true;
}
void crypto_ops::generate_ring_signature(const hash &prefix_hash, const key_image &image,
const public_key *const *pubs, size_t pubs_count,
const secret_key &sec, size_t sec_index,
signature *sig) {
lock_guard<mutex> lock(random_lock);
size_t i;
ge_p3 image_unp;
ge_dsmp image_pre;
ec_scalar sum, k, h;
rs_comm *const buf = reinterpret_cast<rs_comm *>(alloca(rs_comm_size(pubs_count)));
assert(sec_index < pubs_count);
#if !defined(NDEBUG)
{
ge_p3 t;
public_key t2;
key_image t3;
assert(sc_check(&sec) == 0);
ge_scalarmult_base(&t, &sec);
ge_p3_tobytes(&t2, &t);
assert(*pubs[sec_index] == t2);
generate_key_image(*pubs[sec_index], sec, t3);
assert(image == t3);
for (i = 0; i < pubs_count; i++) {
assert(check_key(*pubs[i]));
}
}
#endif
if (ge_frombytes_vartime(&image_unp, &image) != 0) {
abort();
}
ge_dsm_precomp(image_pre, &image_unp);
sc_0(&sum);
buf->h = prefix_hash;
for (i = 0; i < pubs_count; i++) {
ge_p2 tmp2;
ge_p3 tmp3;
if (i == sec_index) {
random_scalar(k);
ge_scalarmult_base(&tmp3, &k);
ge_p3_tobytes(&buf->ab[i].a, &tmp3);
hash_to_ec(*pubs[i], tmp3);
ge_scalarmult(&tmp2, &k, &tmp3);
ge_tobytes(&buf->ab[i].b, &tmp2);
} else {
random_scalar(sig[i].c);
random_scalar(sig[i].r);
if (ge_frombytes_vartime(&tmp3, &*pubs[i]) != 0) {
abort();
}
ge_double_scalarmult_base_vartime(&tmp2, &sig[i].c, &tmp3, &sig[i].r);
ge_tobytes(&buf->ab[i].a, &tmp2);
hash_to_ec(*pubs[i], tmp3);
ge_double_scalarmult_precomp_vartime(&tmp2, &sig[i].r, &tmp3, &sig[i].c, image_pre);
ge_tobytes(&buf->ab[i].b, &tmp2);
sc_add(&sum, &sum, &sig[i].c);
}
}
hash_to_scalar(buf, rs_comm_size(pubs_count), h);
sc_sub(&sig[sec_index].c, &h, &sum);
sc_mulsub(&sig[sec_index].r, &sig[sec_index].c, &sec, &k);
}
