Ethereum Protocol 101 by Mario Havel

​Course 3/7: Hashing, Data Structures & Merkle Trees.

​Ethereum’s security is built on one core primitive: hashing.

​In this session, we explore:

• ​Why hashes are foundational to protocol design

• ​Hash tables and efficient data lookup

• ​How large datasets can be verified efficiently

• ​The invention of Merkle trees by Ralph Merkle

• ​Why Merkle trees are critical to blockchains

​We’ll walk through:

• ​Leaves, nodes, and the Merkle root

• ​How changes propagate through a tree

• ​How inclusion proofs work

• ​Why verification requires only a branch — not the whole dataset

​Every block in Ethereum contains a Merkle tree of transactions. A single altered transaction changes the root — and invalidates the chain that follows.

​We’ll also briefly cover variations used in production systems:

• ​Merkle Patricia Trees

• ​Sparse Merkle Trees

• ​Merkle DAGs (used in systems like IPFS)

​If you want to understand how Ethereum makes trust-minimized verification possible, this session is essential.