pragma solidity ^0.8.0;
import "./PairingsBn254.sol";
library TranscriptLib {
// flip 0xe000000000000000000000000000000000000000000000000000000000000000;
uint256 constant FR_MASK = 0x1fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff;
uint32 constant DST_0 = 0;
uint32 constant DST_1 = 1;
uint32 constant DST_CHALLENGE = 2;
struct Transcript {
bytes32 state_0;
bytes32 state_1;
uint32 challenge_counter;
}
function new_transcript() internal pure returns (Transcript memory t) {
t.state_0 = bytes32(0);
t.state_1 = bytes32(0);
t.challenge_counter = 0;
}
function update_with_u256(Transcript memory self, uint256 value) internal pure {
bytes32 old_state_0 = self.state_0;
self.state_0 = keccak256(abi.encodePacked(DST_0, old_state_0, self.state_1, value));
self.state_1 = keccak256(abi.encodePacked(DST_1, old_state_0, self.state_1, value));
}
function update_with_fr(Transcript memory self, PairingsBn254.Fr memory value) internal pure {
update_with_u256(self, value.value);
}
function update_with_g1(Transcript memory self, PairingsBn254.G1Point memory p) internal pure {
update_with_u256(self, p.X);
update_with_u256(self, p.Y);
}
function get_challenge(Transcript memory self) internal pure returns(PairingsBn254.Fr memory challenge) {
bytes32 query = keccak256(abi.encodePacked(DST_CHALLENGE, self.state_0, self.state_1, self.challenge_counter));
self.challenge_counter += 1;
challenge = PairingsBn254.Fr({value: uint256(query) & FR_MASK});
}
}