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ringct: the commitment mask is now deterministic

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saves space in the tx and is safe

Found by knaccc
This commit is contained in:
moneromooo-monero
2019-01-08 16:05:18 +00:00
parent 99d946e619
commit 7d37598158
7 changed files with 55 additions and 63 deletions
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56
src/ringct/rctOps.cpp
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@@ -672,36 +672,56 @@ namespace rct {
// where C= aG + bH
static key ecdhHash(const key &k)
{
char data[38];
rct::key hash;
memcpy(data, "amount", 6);
memcpy(data + 6, &k, sizeof(k));
cn_fast_hash(hash, data, sizeof(data));
return hash;
char data[38];
rct::key hash;
memcpy(data, "amount", 6);
memcpy(data + 6, &k, sizeof(k));
cn_fast_hash(hash, data, sizeof(data));
return hash;
}
static void xor8(key &v, const key &k)
{
for (int i = 0; i < 8; ++i)
v.bytes[i] ^= k.bytes[i];
for (int i = 0; i < 8; ++i)
v.bytes[i] ^= k.bytes[i];
}
void ecdhEncode(ecdhTuple & unmasked, const key & sharedSec, bool short_amount) {
key sharedSec1 = hash_to_scalar(sharedSec);
key sharedSec2 = hash_to_scalar(sharedSec1);
key genCommitmentMask(const key &sk)
{
char data[15 + sizeof(key)];
memcpy(data, "commitment_mask", 15);
memcpy(data + 15, &sk, sizeof(sk));
key scalar;
hash_to_scalar(scalar, data, sizeof(data));
return scalar;
}
void ecdhEncode(ecdhTuple & unmasked, const key & sharedSec, bool v2) {
//encode
sc_add(unmasked.mask.bytes, unmasked.mask.bytes, sharedSec1.bytes);
if (short_amount)
if (v2)
{
unmasked.mask = zero();
xor8(unmasked.amount, ecdhHash(sharedSec));
}
else
{
key sharedSec1 = hash_to_scalar(sharedSec);
key sharedSec2 = hash_to_scalar(sharedSec1);
sc_add(unmasked.mask.bytes, unmasked.mask.bytes, sharedSec1.bytes);
sc_add(unmasked.amount.bytes, unmasked.amount.bytes, sharedSec2.bytes);
}
}
void ecdhDecode(ecdhTuple & masked, const key & sharedSec, bool short_amount) {
key sharedSec1 = hash_to_scalar(sharedSec);
key sharedSec2 = hash_to_scalar(sharedSec1);
void ecdhDecode(ecdhTuple & masked, const key & sharedSec, bool v2) {
//decode
sc_sub(masked.mask.bytes, masked.mask.bytes, sharedSec1.bytes);
if (short_amount)
if (v2)
{
masked.mask = genCommitmentMask(sharedSec);
xor8(masked.amount, ecdhHash(sharedSec));
}
else
{
key sharedSec1 = hash_to_scalar(sharedSec);
key sharedSec2 = hash_to_scalar(sharedSec1);
sc_sub(masked.mask.bytes, masked.mask.bytes, sharedSec1.bytes);
sc_sub(masked.amount.bytes, masked.amount.bytes, sharedSec2.bytes);
}
}
}