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Merge pull request #1412 from ethereum/vbuterin-patch-1

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Refactor Merkle proof verification
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Diederik Loerakker 2019-10-23 17:32:26 +08:00 committed by GitHub
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specs/light_client/merkle_proofs.md
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@ -289,23 +289,27 @@ def get_helper_indices(indices: Sequence[GeneralizedIndex]) -> Sequence[Generali
Now we provide the Merkle proof verification functions. First, for single item proofs: Now we provide the Merkle proof verification functions. First, for single item proofs:
```python ```python
def verify_merkle_proof(leaf: Hash, proof: Sequence[Hash], index: GeneralizedIndex, root: Hash) -> bool: def calculate_merkle_root(leaf: Hash, proof: Sequence[Hash], index: GeneralizedIndex) -> Hash:
assert len(proof) == get_generalized_index_length(index) assert len(proof) == get_generalized_index_length(index)
for i, h in enumerate(proof): for i, h in enumerate(proof):
if get_generalized_index_bit(index, i): if get_generalized_index_bit(index, i):
leaf = hash(h + leaf) leaf = hash(h + leaf)
else: else:
leaf = hash(leaf + h) leaf = hash(leaf + h)
return leaf == root return leaf
```
```python
def verify_merkle_proof(leaf: Hash, proof: Sequence[Hash], index: GeneralizedIndex, root: Hash) -> bool:
return calculate_merkle_root(leaf, proof, index) == root
``` ```
Now for multi-item proofs: Now for multi-item proofs:
```python ```python
def verify_merkle_multiproof(leaves: Sequence[Hash], def calculate_multi_merkle_root(leaves: Sequence[Hash],
proof: Sequence[Hash], proof: Sequence[Hash],
indices: Sequence[GeneralizedIndex], indices: Sequence[GeneralizedIndex]) -> Hash:
root: Hash) -> bool:
assert len(leaves) == len(indices) assert len(leaves) == len(indices)
helper_indices = get_helper_indices(indices) helper_indices = get_helper_indices(indices)
assert len(proof) == len(helper_indices) assert len(proof) == len(helper_indices)
@ -324,7 +328,15 @@ def verify_merkle_multiproof(leaves: Sequence[Hash],
) )
keys.append(GeneralizedIndex(k // 2)) keys.append(GeneralizedIndex(k // 2))
pos += 1 pos += 1
return objects[GeneralizedIndex(1)] == root return objects[GeneralizedIndex(1)]
``` ```
Note that the single-item proof is a special case of a multi-item proof; a valid single-item proof verifies correctly when put into the multi-item verification function (making the natural trivial changes to input arguments, `index -> [index]` and `leaf -> [leaf]`). ```python
def verify_merkle_multiproof(leaves: Sequence[Hash],
proof: Sequence[Hash],
indices: Sequence[GeneralizedIndex],
root: Hash) -> bool:
return calculate_multi_merkle_root(leaves, proof, indices) == root
```
Note that the single-item proof is a special case of a multi-item proof; a valid single-item proof verifies correctly when put into the multi-item verification function (making the natural trivial changes to input arguments, `index -> [index]` and `leaf -> [leaf]`). Note also that `calculate_merkle_root` and `calculate_multi_merkle_root` can be used independently to compute the new Merkle root of a proof with leaves updated.