To start use darf signature you need to have address in ethereum system (https://ethereum.org/) signature.sol - code of smart contract you can use http://remix.ethereum.org for deploy of smart contract and testrpc for testing of you signature How it works here https://www.youtube.com/watch?v=3EI5ifhAk4c&t=142s
It is only test module If it is interesting for you in production go to http://darfchain.com
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