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37 lines
1004 B
37 lines
1004 B
pragma solidity ^0.4.4;
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/*
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* Proof of Existence example contract
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* see https://medium.com/zeppelin-blog/the-hitchhikers-guide-to-smart-contracts-in-ethereum-848f08001f05
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*/
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contract ProofOfExistence {
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mapping (bytes32 => bool) public proofs;
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// store a proof of existence in the contract state
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function storeProof(bytes32 proof) {
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proofs[proof] = true;
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}
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// calculate and store the proof for a document
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function notarize(string document) {
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var proof = calculateProof(document);
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storeProof(proof);
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}
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// helper function to get a document's sha256
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function calculateProof(string document) constant returns (bytes32) {
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return sha256(document);
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}
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// check if a document has been notarized
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function checkDocument(string document) constant returns (bool) {
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var proof = calculateProof(document);
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return hasProof(proof);
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}
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// returns true if proof is stored
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function hasProof(bytes32 proof) constant returns (bool) {
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return proofs[proof];
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}
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}
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