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Fix vulnerability in get_peaks() pseudocode 

This addresses finding NCC-1908_Zcash-002.
This commit is contained in:
Jack Grigg 2020-03-04 09:12:53 +13:00 committed by Daira Hopwood
parent 5b411837f4
commit 6d64ce0c87
1 changed files with 9 additions and 12 deletions
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21
zip-0221.rst
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@ -451,21 +451,18 @@ With each new block ``B_n``, we append a new MMR leaf node corresponding to bloc
def get_peaks(node: ZcashMMRNode) -> List[ZcashMMRNode]:
peaks: List[ZcashMMRNode] = []
left_child = node.left_child
right_child = node.right_child
# Get number of leaves.
leaves = latest_height - earliest_height + 1
# find the number of leaves in the subtree
left_leaves = left_child.latest_height - left_child.earliest_height + 1
right_leaves = right_child.latest_height - right_child.earliest_height + 1
if (left_leaves & (left_leaves - 1)) == 0:
peaks.append(left_child)
# Check if the number of leaves is a power of two.
if (leaves & (leaves - 1)) == 0:
# Tree is full, hence a single peak. This also covers the
# case of a single isolated leaf.
peaks.append(node)
else:
# If the number of leaves is not a power of two, then this
# node must be internal, and cannot be a peak.
peaks.extend(get_peaks(left_child))
if (right_leaves & (right_leaves - 1)) == 0:
peaks.append(right_child)
else:
peaks.extend(get_peaks(right_child))
return peaks