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[WIP] Crypto-economic Aggregate Signatures #34

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[WIP] Crypto-economic Aggregate Signatures #34

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27c3199
add contract optimization
johannbarbie Jul 11, 2018
e52dcef
first attempt at cryptoeconomic aggregate signatures
johannbarbie Jul 11, 2018
c42e734
first test for CAS
johannbarbie Jul 12, 2018
995fef6
added more tests
johannbarbie Jul 12, 2018
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132 changes: 106 additions & 26 deletions contracts/ParsecBridge.sol
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Expand Up @@ -65,7 +65,7 @@ contract ParsecBridge {
uint32 parentIndex; // the position of this node in the Parent's children list
uint8 slot;
uint32 timestamp;
uint64 reward;
uint256 sigs;
bytes32[] children; // unordered list of children below this node
}
mapping(bytes32 => Period) public periods;
Expand All @@ -86,6 +86,14 @@ contract ParsecBridge {
}
mapping(bytes32 => Exit) public exits;

struct Challenge {
uint64 stake;
address signer;
uint32 finalizationEpoch;
}

mapping(bytes32 => mapping(uint256 => Challenge)) challenges;


constructor(uint256 _epochLength, uint256 _maxReward, uint256 _parentBlockInterval, uint256 _exitDuration) public {
// init genesis preiod
Expand Down Expand Up @@ -256,13 +264,21 @@ contract ParsecBridge {
averageGasPrice = averageGasPrice - (averageGasPrice / 15) + (tx.gasprice / 15);
}

function submitPeriod(uint256 _slotId, bytes32 _prevHash, bytes32 _root) public {
function countSigs(uint256 _sigs, uint256 _epochLength) internal pure returns (uint256 count) {
for (uint i = 256; i >= 256 - _epochLength; i--) {
count += uint8(_sigs >> i) & 0x01;
}
}

function submitPeriod(uint256 _slotId, bytes32 _prevHash, bytes32 _root, uint256 _sigs) public {
// check parent node exists
require(periods[_prevHash].parent > 0);
// check that same root not submitted yet
require(periods[_root].height == 0);
// check slot
require(_slotId < epochLength);
// count sigs
require(countSigs(_sigs, epochLength) > epochLength.mul(2).div(3));
Slot storage slot = slots[_slotId];
require(slot.signer == msg.sender);
if (slot.activationEpoch > 0) {
Expand All @@ -285,6 +301,7 @@ contract ParsecBridge {
// store the period
Period memory newPeriod;
newPeriod.parent = _prevHash;
newPeriod.sigs = _sigs;
newPeriod.height = uint32(newHeight);
newPeriod.slot = uint8(_slotId);
newPeriod.timestamp = uint32(block.timestamp);
Expand All @@ -310,6 +327,93 @@ contract ParsecBridge {
}
}

function getChallenge(bytes32 _period, uint256 _slotId) public constant returns (uint256, address, uint256) {
return (challenges[_period][_slotId].stake, challenges[_period][_slotId].signer, challenges[_period][_slotId].finalizationEpoch);

}

function challengeSig(bytes32 _period, uint256 _slotId) public {
require(_slotId < epochLength);
// check that sig was actually 1
require(uint8(periods[_period].sigs >> _slotId) & 0x01 == 1);
// check that challenge doesn't exist yet
require(challenges[_period][_slotId].signer == 0x0);
// check that challenge submitted for previous epoche, and current epoch has not progressed more than 1/3
uint256 finalizationEpoch;
if (periods[_period].height <= lastEpochBlockHeight) {
// check that challenge not older than 4/3 epoch
require(periods[tipHash].height - periods[_period].height < epochLength.mul(32).mul(4).div(3));
// check that current epoch not older than 1/3 epochLength
require(periods[tipHash].height - lastEpochBlockHeight < epochLength.mul(32).div(3));
finalizationEpoch = lastCompleteEpoch;
} else {
// challenge submitted for current epoch, nothing to check
finalizationEpoch = lastCompleteEpoch + 1;
}
// transfer funds for bond
tokens[0].addr.transferFrom(msg.sender, this, 100);
// create challenge object
challenges[_period][_slotId] = Challenge(100, msg.sender, uint32(finalizationEpoch));
}

function answerSig(bytes32 _period, uint256 _slotId, uint8 _v, bytes32 _r, bytes32 _s) public {
// check that challenge does exist
require(challenges[_period][_slotId].stake > 0);
// check signature
require(ecrecover(_period, _v, _r, _s) == slots[_slotId].signer);
// slash challenger
slots[_slotId].stake += challenges[_period][_slotId].stake / 2;
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tokens come out of thin air?

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what happens to the second half of the slashed stake?

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second half should be burned. so that the slash function is not used as a function to unstake faster than allowed.

// delete challenge
delete challenges[_period][_slotId];
}

function slashSig(bytes32 _period, uint256 _slotId) public {
Challenge memory challenge = challenges[_period][_slotId];
// check that challenge does exist
require(challenge.stake > 0);
// check that we are in next epoch
require(periods[_period].height <= lastEpochBlockHeight);
// check that 2/3 of next epoch passed
require(periods[tipHash].height - lastEpochBlockHeight >= epochLength.mul(32).mul(2).div(3));
// check that challenge not older than 2 epochs
require(periods[tipHash].height - periods[_period].height < epochLength.mul(32).mul(2));
// slash validator
slash(periods[_period].slot, challenge.stake);
// pay out challenger
tokens[0].addr.transfer(challenge.signer, challenge.stake / 2);
// TODO burn rest of tokens in total supply
// delete challenge
delete challenges[_period][_slotId];
}

function slashDoubleSig(uint256 _slotId, bytes32 _root1, uint8 _v1, bytes32 _r1, bytes32 _s1, bytes32 _root2, uint8 _v2, bytes32 _r2, bytes32 _s2) public {
// check roots are different
require(_root1 != _root2);
// check _roots exist and have same height
require(periods[_root1].height == periods[_root2].height);
// check that signer has slot
address signer = ecrecover(_root1, _v1, _r1, _s1);
require(slots[_slotId].signer == signer);
// check that second signature also mathches signer
require(ecrecover(_root2, _v2, _r2, _s2) == signer);
// slash signer
slash(_slotId, 100);
}

function slash(uint256 _slotId, uint256 _value) public {
require(_slotId < epochLength);
Slot storage slot = slots[_slotId];
require(slot.stake > 0);
uint256 prevStake = slot.stake;
slot.stake = (_value >= slot.stake) ? 0 : slot.stake - uint64(_value);
// if slot became empty by slashing
if (prevStake > 0 && slot.stake == 0) {
//emit ValidatorLeave(slot.signer, _slotId, slot.tendermint, lastCompleteEpoch + 1);
slot.activationEpoch = 0;
// activate next guy
}
}
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maybe emit Slash event here?


function deletePeriod(bytes32 hash) internal {
Period storage parent = periods[periods[hash].parent];
uint256 i = periods[hash].parentIndex;
Expand All @@ -336,7 +440,6 @@ contract ParsecBridge {
signer = address(_txData[2]);
}


/*
* _txData = [ 32b periodHash, (1b Proofoffset, 8b pos, ..00.., 1b txData), 32b txData, 32b proof, 32b proof ]
*
Expand Down Expand Up @@ -408,29 +511,6 @@ contract ParsecBridge {
slash(p.slot, 50);
}

function slash(uint256 _slotId, uint256 _value) public {
require(_slotId < epochLength);
Slot storage slot = slots[_slotId];
require(slot.stake > 0);
uint256 prevStake = slot.stake;
slot.stake = (_value >= slot.stake) ? 0 : slot.stake - uint64(_value);
// if slot became empty by slashing
if (prevStake > 0 && slot.stake == 0) {
emit ValidatorLeave(slot.signer, _slotId, slot.tendermint, lastCompleteEpoch + 1);
slot.activationEpoch = 0;
if (slot.newStake > 0) {
// someone in queue
activate(_slotId);
} else {
// clean out account
slot.owner = 0;
slot.signer = 0;
slot.tendermint = 0x0;
slot.stake = 0;
}
}
}

/*
* Add funds
*/
Expand Down