Method get_root

final-spv/src/merkle_tree.rs:239–267

Calculates the Merkle root given a leaf transaction ID (`txid`, which is a `mid_state_txid`) and the Merkle proof path (sibling nodes from the "mid-state" tree). The core of the SPV security enhancement is here: Each `merkle_proof` element (a sibling node from the mid-state tree) is first hashed with `calculate_sha256`. This transformed hash is then used in the standard Bitcoin Merkle combination

(&self, txid: [u8; 32])

    /// from the leaf transaction IDs, preventing cross-interpretation and related attacks.
    /// The final hash should be the main Bitcoin block Merkle root.
    pub fn get_root(&self, txid: [u8; 32]) -> [u8; 32] {
        // txid is the leaf (e.g., mid_state_txid)
        let mut preimage: [u8; 64] = [0; 64];
        let mut combined_hash: [u8; 32] = txid; // Start with the leaf txid
        let mut index = self.idx;
        let mut level: u32 = 0;
        while level < self.merkle_proof.len() as u32 {
            // Get the sibling node from the mid-state tree proof path
            let mid_state_sibling_node = self.merkle_proof[level as usize];
            // Secure SPV step: transform the mid-state sibling node by SHA256-ing it
            // before using it in the double-SHA256 combination.
            let processed_sibling_hash = calculate_sha256(&mid_state_sibling_node);

            if index % 2 == 0 {
                // `combined_hash` is the left child
                preimage[..32].copy_from_slice(&combined_hash);
                preimage[32..].copy_from_slice(&processed_sibling_hash); // Use the SHA256'd mid-state sibling
                combined_hash = calculate_double_sha256(&preimage);
            } else {
                // `combined_hash` is the right child
                preimage[..32].copy_from_slice(&processed_sibling_hash); // Use the SHA256'd mid-state sibling
                preimage[32..].copy_from_slice(&combined_hash);
                combined_hash = calculate_double_sha256(&preimage);
            }
            level += 1;
            index /= 2;
        }
        combined_hash // This should be the Bitcoin block's Merkle root
    }
}

/// Verifies a Merkle proof against a given root using the "mid-state" tree approach.