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avoiding_common_attacks.md

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Contract security measures

SWC-103 (Floating pragma)

Specific compiler pragma pragma solidity 0.5.16; is used in contracts to avoid accidental bug inclusion through outdated compiler versions.

SWC-105 (Unprotected Ether Withdrawal)

The DocumentSigner as a part of payable documents feature implements access controls so withdrawals can only be triggered by allowed parties.

Function signDocument(string calldata documentHash) is used for signing a document. This function will perform signatory related checks such as signatoryExist(documentHash, msg.sender) and signatoryDidNotSign(documentHash, msg.sender) which will ensure that only allowed signatory which have not yet signed the specified document can sign it and withdraw the funds (if specified) from the smart contract.

Function signDocument(string calldata documentHash) will always check if there is an amount of ether specified and greater than zero if (signatories[i].amountToBePaid > 0)and the withdrawal amount will be predefined and read from the amountToBePaid storage variable within the signatory structure so the signatory does not have any influence on the value they're withdrawing. The amountToBePaid is something that only can be modified by the document owner who sent that ether amount to the smart contract while adding the signatory.

SWC-107 (Reentrancy / Checks-Effects-Interactions)

DocumentSigner smart contract inside withdrawal-able function signDocument(string calldata documentHash) makes sure that all internal state changes are performed before the call is executed.

  1. Modifier runs first signatoryDidNotSign(documentHash, msg.sender)
  2. Document is marked as signed documents[documentHash].signatures[msg.sender] = true;
  3. Amount to be paid is checked next if (signatories[i].amountToBePaid > 0)
  4. Amount to be paid is set to zero documents[documentHash].signatories[i].amountToBePaid = 0;
  5. Transfer is executed at the end msg.sender.transfer(signatories[i].amountToBePaid);

Modifiers used only for validation

All modifiers in contract(s) only validate data with require statements.

Pull over push

All functions that modify state are based on receiving calls rather than making contract calls.