The Proof operation in the MerklePatriciaTree provides a way to validate a specific [key, value] pair's existence (or non-existence) without requiring the entire trie. This operation is especially useful in scenarios where a lightweight client wants to verify a particular data piece without downloading and storing the complete trie.
🪜 Steps to Generate a Proof:
Initialize Proof Data: Begin by creating an empty list to hold the nodes you'll traverse during the proof generation.
Traverse the Trie: Navigate through the trie, following the path dictated by the key for which you want to generate a proof.
Leaf Node Handling: If you encounter a leaf node:
Check if the leaf node's key matches the desired key.
If it matches, add the leaf node to the proof data list.
Branch Node Handling: When encountering a branch node:
Add the entire branch node to the proof list, as it contains paths for multiple keys.
Continue the traversal following the path segment corresponding to the next nibble in the key.
Extension Node Handling: Upon finding an extension node:
Add the extension node to the proof data list, as it represents a shared path among multiple keys.
Proceed down the path indicated by the extension node's nibbles.
HashNode Encountered: If you come across a HashNode:
Fetch the actual node it refers to.
Continue with the normal proof generation process for the fetched node.
Compile the Proof: Once traversal is complete, compile all the nodes you've added to the proof data list. This list represents the minimum set of nodes required to validate the [key, value] pair's existence or non-existence.
Return the Proof Data: The compiled list of nodes is the proof. It can be sent to any client wishing to verify a specific key's value within the trie.
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