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Merge pull request #2 from ethereum-attestation-service/offchain-veri…
…fication Add an example for an offchain attestation verification contract (+ lots of refactoring)
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| // SPDX-License-Identifier: MIT | ||
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| pragma solidity 0.8.22; | ||
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| import { IEAS, Attestation } from "@ethereum-attestation-service/eas-contracts/contracts/IEAS.sol"; | ||
| import { SchemaResolver } from "@ethereum-attestation-service/eas-contracts/contracts/resolver/SchemaResolver.sol"; | ||
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| /// @title LogResolver | ||
| /// @notice A sample schema resolver that logs a uint256 input. | ||
| contract LogResolver is SchemaResolver { | ||
| /// @notice Emitted to log a uint256 value. | ||
| /// @param value The attested value. | ||
| event Attested(uint256 value); | ||
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| /// @notice Emitted to log a uint256 value. | ||
| /// @param value The attested value. | ||
| event Revoked(uint256 value); | ||
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| /// @notice Creates a new LogResolver instance. | ||
| constructor(IEAS eas) SchemaResolver(eas) {} | ||
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| /// @notice An example resolver onAttest callback that decodes a uint256 value and just logs it. | ||
| /// @param attestation The new attestation. | ||
| /// @return Whether the attestation is valid. | ||
| function onAttest(Attestation calldata attestation, uint256 /*value*/) internal override returns (bool) { | ||
| uint256 value = abi.decode(attestation.data, (uint256)); | ||
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| emit Attested(value); | ||
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| return true; | ||
| } | ||
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| /// @notice An example resolver onRevoke fallthrough callback (which currently doesn't do anything). | ||
| /// @return Whether the attestation can be revoked. | ||
| function onRevoke(Attestation calldata attestation, uint256 /*value*/) internal override returns (bool) { | ||
| uint256 value = abi.decode(attestation.data, (uint256)); | ||
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| emit Revoked(value); | ||
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| return true; | ||
| } | ||
| } |
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| // SPDX-License-Identifier: MIT | ||
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| pragma solidity 0.8.22; | ||
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| import { IEAS } from "@ethereum-attestation-service/eas-contracts/contracts/IEAS.sol"; | ||
| import { SchemaRecord } from "@ethereum-attestation-service/eas-contracts/contracts/ISchemaRegistry.sol"; | ||
| import { EMPTY_UID, Signature } from "@ethereum-attestation-service/eas-contracts/contracts/Common.sol"; | ||
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| import { SignatureChecker } from "@openzeppelin/contracts/utils/cryptography/SignatureChecker.sol"; | ||
| import { Strings } from "@openzeppelin/contracts/utils/Strings.sol"; | ||
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| import { EIP712Verifier } from "./eip712/EIP712Verifier.sol"; | ||
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| /// @title OffchainAttestationVerifier | ||
| /// @notice Offchain Attestation Verifier - Example | ||
| contract OffchainAttestationVerifier is EIP712Verifier { | ||
| /// @notice A struct representing an offchain attestation request. | ||
| struct OffchainAttestation { | ||
| uint16 version; // The version of the attestation. | ||
| address attester; // The attester of the attestation. | ||
| bytes32 schema; // The unique identifier of the schema. | ||
| address recipient; // The recipient of the attestation. | ||
| uint64 time; // The time when the attestation was signed. | ||
| uint64 expirationTime; // The time when the attestation expires (Unix timestamp). | ||
| bool revocable; // Whether the attestation is revocable. | ||
| bytes32 refUID; // The UID of the related attestation. | ||
| bytes data; // Custom attestation data. | ||
| Signature signature; // The ECDSA signature data. | ||
| } | ||
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| // Offchain attestation versions. | ||
| uint16 private constant LEGACY = 0; | ||
| uint16 private constant VERSION1 = 1; | ||
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| // The hash of the data type used to relay calls to the attest function. It's the value of | ||
| // keccak256("Attestation(bytes32 schema,address recipient,uint64 time,uint64 expirationTime,bool revocable,bytes32 refUID,bytes data)"). | ||
| bytes32 private constant LEGACY_ATTEST_TYPEHASH = | ||
| 0x2fcbc49c85ccde58f6986371b0828354351185c921aebbaace3e89e0e023b25d; | ||
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| // The hash of the data type used to relay calls to the attest function. It's the value of | ||
| // keccak256("Attest(uint16 version,bytes32 schema,address recipient,uint64 time,uint64 expirationTime,bool revocable,bytes32 refUID,bytes data)"). | ||
| bytes32 private constant VERSION1_ATTEST_TYPEHASH = | ||
| 0x9a1ef129b3715afc513574bddcf4404e21b0296e3ca20fec532fe1ec8d0932ec; | ||
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| // The address of the global EAS contract. | ||
| IEAS private immutable _eas; | ||
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| /// @notice Creates a new Attester instance. | ||
| /// @param eas The address of the global EAS contract. | ||
| constructor(IEAS eas) EIP712Verifier("EAS Attestation", eas.version(), address(eas)) { | ||
| _eas = eas; | ||
| } | ||
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| /// @notice Returns the EAS. | ||
| function getEAS() external view returns (IEAS) { | ||
| return _eas; | ||
| } | ||
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| /// @notice Verify the offchain attestation. | ||
| /// @param attestation The offchain attestation to verify. | ||
| /// @return The status of the verification. | ||
| function verify(OffchainAttestation calldata attestation) external view returns (bool) { | ||
| if (attestation.attester == address(0)) { | ||
| return false; | ||
| } | ||
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| // Verify that the version is known. | ||
| uint16 version = attestation.version; | ||
| if (version > VERSION1) { | ||
| return false; | ||
| } | ||
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| // Verify that the time of the attestation isn't in the future. | ||
| if (attestation.time > _time()) { | ||
| return false; | ||
| } | ||
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| // Verify that the schema exists. | ||
| SchemaRecord memory schemaRecord = _eas.getSchemaRegistry().getSchema(attestation.schema); | ||
| if (schemaRecord.uid == EMPTY_UID) { | ||
| return false; | ||
| } | ||
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| // Verify that the referenced attestation exists. | ||
| if (attestation.refUID != EMPTY_UID && !_eas.isAttestationValid(attestation.refUID)) { | ||
| return false; | ||
| } | ||
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| // Verify the EIP712/EIP1271 signature. | ||
| bytes32 hash; | ||
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| // Derive the right typed data hash based on the offchain attestation version. Please note that due to previous | ||
| // checks, don't need a case for the unknown version below. | ||
| if (version == LEGACY) { | ||
| hash = _hashTypedDataLegacy(attestation); | ||
| } else if (version == VERSION1) { | ||
| hash = _hashTypedDataVersion1(attestation); | ||
| } | ||
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| Signature memory signature = attestation.signature; | ||
| if ( | ||
| !SignatureChecker.isValidSignatureNow( | ||
| attestation.attester, | ||
| hash, | ||
| abi.encodePacked(signature.r, signature.s, signature.v) | ||
| ) | ||
| ) { | ||
| return false; | ||
| } | ||
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| return true; | ||
| } | ||
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| /// @dev Returns the legacy (version 0) attestation typed data hash | ||
| /// @param attestation The offchain attestation to verify. | ||
| /// @return The typed data hash. | ||
| function _hashTypedDataLegacy(OffchainAttestation calldata attestation) private view returns (bytes32) { | ||
| return | ||
| _hashTypedDataV4( | ||
| keccak256( | ||
| abi.encode( | ||
| LEGACY_ATTEST_TYPEHASH, | ||
| attestation.schema, | ||
| attestation.recipient, | ||
| attestation.time, | ||
| attestation.expirationTime, | ||
| attestation.revocable, | ||
| attestation.refUID, | ||
| keccak256(attestation.data) | ||
| ) | ||
| ) | ||
| ); | ||
| } | ||
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| /// @dev Returns the legacy (version 0) attestation typed data hash | ||
| /// @param attestation The offchain attestation to verify. | ||
| /// @return The typed data hash. | ||
| function _hashTypedDataVersion1(OffchainAttestation calldata attestation) private view returns (bytes32) { | ||
| return | ||
| _hashTypedDataV4( | ||
| keccak256( | ||
| abi.encode( | ||
| VERSION1_ATTEST_TYPEHASH, | ||
| VERSION1, | ||
| attestation.schema, | ||
| attestation.recipient, | ||
| attestation.time, | ||
| attestation.expirationTime, | ||
| attestation.revocable, | ||
| attestation.refUID, | ||
| keccak256(attestation.data) | ||
| ) | ||
| ) | ||
| ); | ||
| } | ||
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| /// @dev Returns the current's block timestamp. This method is overridden during tests and used to simulate the | ||
| /// current block time. | ||
| function _time() internal view virtual returns (uint64) { | ||
| return uint64(block.timestamp); | ||
| } | ||
| } |
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