[BUG]: Merkle Sibling Index Inconsistency in `generate_merkle_proof()` May Failures

[Arpitsh7]

Bug Description

Description

There is a structural inconsistency in how odd-length tree levels are handled between compute_merkle_root() and generate_merkle_proof(). While both functions produce correct results today, they use different strategies for padding odd nodes — meaning any future modification to one function without the other will cause proofs to silently fail against the root.

Additionally, the sibling index calculation uses a raw XOR (index ^ 1), which is only safe because of the pre-padding step above it. This is fragile and non-obvious.

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Root Cause

Function	Odd-node strategy
compute_merkle_root()	Inline: right = left if i+1 >= len(leaves)
generate_merkle_proof()	Pre-pads: leaves.append(leaves[-1])

The sibling calculation in generate_merkle_proof():

# Fragile — only safe due to pre-padding above
sibling_index = index ^ 1

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Expected Behaviour

Both functions should use the same, explicit odd-node strategy, and sibling index calculation should be self-evidently safe without relying on a prior mutation of the array.

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Suggested Fix

Replace the XOR with an explicit parity check:

# In generate_merkle_proof()
sibling_index = index - 1 if index % 2 == 1 else index + 1
# Guard: ensure sibling doesn't exceed bounds (handles odd levels)
if sibling_index >= len(leaves):
    sibling_index = index  # duplicate self

And unify the padding strategy across both functions for long-term maintainability.

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Impact

• Merkle proofs may silently fail if either function is modified independently

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Medium - Feature works but has issues

Code of Conduct

• I have joined the Discord server and will post updates there
• I have searched existing issues to avoid duplicates

[Arpitsh7]

Hi @Archit381 please assign me this issue