December 2018
Beginner to intermediate
564 pages
17h 34m
English
Content preview from Blockchain Developer's Guide
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Proof of existence, integrity, and ownership contract
Let's write a Solidity contract that can prove file ownership without revealing the actual file. It can prove that the file existed at a particular time and finally check for document integrity.
We will achieve proof of ownership by storing the hash of the file and the owner's name as pairs. We will achieve proof of existence by storing the hash of the file and the block timestamp as pairs. Finally, storing the hash itself proves the file integrity; that is, if the file was modified, then its hash will change and the contract won't be able to find any such file, therefore proving that the file was modified.
Here is the code for the smart contract to achieve all this:
contract Proof { ...Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.