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Optimize publicKey method by precomputing G powers #8

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Optimize publicKey method by precomputing G powers #8

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43 changes: 36 additions & 7 deletions ec.sol
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Original file line number Diff line number Diff line change
Expand Up @@ -7,9 +7,29 @@ contract EC {
uint256 constant n = 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEFFFFFC2F;
uint256 constant a = 0;
uint256 constant b = 7;
uint256[] public gxs;
uint256[] public gys;
uint256[] public gzs;

function EC()
{
gxs.push(gx);
gys.push(gy);
gzs.push(1);
}

function prepare(uint count) public
{
require(gxs.length < 256);
uint256 x = gxs[gxs.length - 1];
uint256 y = gys[gys.length - 1];
uint256 z = gzs[gzs.length - 1];
for (uint j = 0; j < count && gxs.length < 256; j++) {
(x,y,z) = _ecDouble(x,y,z);
gxs.push(x);
gys.push(y);
gzs.push(z);
}
}

function _jAdd( uint256 x1,uint256 z1,
Expand Down Expand Up @@ -154,13 +174,22 @@ contract EC {
function publicKey(uint256 privKey) constant
returns(uint256 qx, uint256 qy)
{
uint256 x;
uint256 y;
uint256 z;
(x,y,z) = _ecMul(privKey, gx, gy, 1);
z = _inverse(z);
qx = mulmod(x , z ,n);
qy = mulmod(y , z ,n);
uint256 acx = 0;
uint256 acy = 0;
uint256 acz = 1;

if (privKey == 0) {
return (0,0);
}

for (uint i = 0; i < 256; i++) {
if (((privKey >> i) & 1) != 0) {
(acx,acy,acz) = _ecAdd(acx,acy,acz, gxs[i],gys[i],gzs[i]);
}
}

acz = _inverse(acz);
(qx,qy) = (mulmod(acx,acz,n),mulmod(acy,acz,n));
}

function deriveKey(uint256 privKey, uint256 pubX, uint256 pubY) constant
Expand Down