Merkle Trees & Transaction Commitments

Why this module exists

Blocks commit to all transactions using a single hash. This enables light clients, efficient verification, and tamper evidence.

1) Merkle root

A Merkle tree reduces N transaction hashes to 1 root:

• Leaves are txids (double SHA-256 of tx bytes)
• Internal nodes hash left || right
• Odd counts duplicate the last hash

This creates a deterministic commitment for the block header.

2) Inclusion proofs

A proof is a path of sibling hashes from leaf to root. A verifier can recompute the root without seeing all transactions.

Properties:

• Proof size is O(log N)
• A single bit-flip in any tx changes the root

3) Security intuition

• Merkle roots prevent silent mutation of tx lists
• Proofs enable SPV-style verification
• Duplicating the last hash avoids ambiguous shapes

What you will build

1. Merkle root computation
2. Merkle proof generation
3. Proof verification

Key takeaways

• Merkle roots bind content and order.
• Proofs are compact and verifiable.
• Consistent tree construction is a consensus rule.