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Add test and docs describing a misuse of MerkleProof #3090

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Jan 31, 2022
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Add test and docs describing a misuse of MerkleProof #3090

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Test and docs describing a misuse of MerkleProof
hoytech Jan 7, 2022
bdd4b7d
lint
frangio Jan 31, 2022
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7 changes: 6 additions & 1 deletion contracts/utils/cryptography/MerkleProof.sol
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Expand Up @@ -11,6 +11,11 @@ pragma solidity ^0.8.0;
* Note: the hashing algorithm should be keccak256 and pair sorting should be enabled.
*
* See `test/utils/cryptography/MerkleProof.test.js` for some examples.
*
* WARNING: You should avoid using leaf values that are 64 bytes long prior to
* hashing, or use a hash function other than keccak256 for hashing leaves.
* This is because the concatenation of a sorted pair of internal nodes in
* the merkle tree could be reinterpreted as a leaf value.
*/
library MerkleProof {
/**
Expand All @@ -28,7 +33,7 @@ library MerkleProof {
}

/**
* @dev Returns the rebuilt hash obtained by traversing a Merklee tree up
* @dev Returns the rebuilt hash obtained by traversing a Merkle tree up
* from `leaf` using `proof`. A `proof` is valid if and only if the rebuilt
* hash matches the root of the tree. When processing the proof, the pairs
* of leafs & pre-images are assumed to be sorted.
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6 changes: 6 additions & 0 deletions test/utils/cryptography/MerkleProof.test.js
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Expand Up @@ -24,6 +24,12 @@ contract('MerkleProof', function (accounts) {
const proof = merkleTree.getHexProof(leaf);

expect(await this.merkleProof.verify(proof, root, leaf)).to.equal(true);

// For demonstration, it is also possible to create valid proofs for certain 64-byte values *not* in elements:
const noSuchLeaf = keccak256(
Buffer.concat([keccak256(elements[0]), keccak256(elements[1])].sort(Buffer.compare)),
);
expect(await this.merkleProof.verify(proof.slice(1), root, noSuchLeaf)).to.equal(true);
});

it('returns false for an invalid Merkle proof', async function () {
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