verifier

School

George Mason University *

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Course

262

Subject

Computer Science

Date

Feb 20, 2024

Type

Pages

Uploaded by ConstableFlamingo152

#!python3 import sys import hashlib from base64 import b64encode, b64decode from collections import deque import re from merkle_utils import MerkleProof, hash_internal_node, hash_leaf merkle_proof_file = "merkle_proof.txt" # File containing the Merkle proof to verify. # Change this to load a different file. MAXHEIGHT = 20 # Max height of Merkle tree # The leaves of our Merkle Tree always have the same value and position. # Therefore, the Merkle root is fixed and is hardcoded here. ROOT = b64decode("1qIbsvuF6FrhNjMD4p06srUye6G4FfFINDDkNfKUpTs=") def read_merkle_proof(filename): """Helper function that reads the leaf data, position of leaf, and Merkle proof from file.""" fp = open(filename, "r") pos = int(re.search('(\d*)$', fp.readline()).group(1)) leaf = re.search('\"(.*)\"',fp.readline()).group(1).encode() fp.readline() hashes = fp.readlines() for i in range(len(hashes)): hashes[i] = b64decode((hashes[i])[2:]) fp.close() return MerkleProof(leaf=leaf, pos=pos, hashes=hashes) def compute_merkle_root_from_merkle_proof(merkle_proof : MerkleProof): """computes a root from the given leaf and Merkle proof.""" pos = merkle_proof.pos hashes = deque(merkle_proof.hashes) root = hash_leaf(merkle_proof.leaf) while hashes: if pos % 2 == 0: left, right = root, hashes.popleft() else: left, right = hashes.popleft(), root root = hash_internal_node(left, right) pos >>= 1 return root # return the computed root def verify_merkle_proof(merkle_proof : MerkleProof): """Verify a merkle proof by generating the merkle root from the leaf, position and hashes and seeing if it produces the correct merkle root. """ # Verify that proof length is correct height = len(merkle_proof.hashes) assert height < MAXHEIGHT, "Proof is too long" computedRoot = compute_merkle_root_from_merkle_proof(merkle_proof) assert ROOT == computedRoot, "Verify failed" print('I verified the Merkle proof: leaf #{} in the committed tree is "{}".\ n'.format(merkle_proof.pos,merkle_proof.leaf.decode("utf-8")))

### Main program if __name__ == "__main__": # Read (leaf data, position of leaf, and proof) from file merkle_proof = read_merkle_proof(merkle_proof_file) # Read optional leaf number from command line # If provided, verify that Merkle proof is for this leaf if len(sys.argv) > 1: pos = int(sys.argv[1]) assert pos == merkle_proof.pos, "Proof is for the wrong leaf" # We already have the hard coded Merkle Root so merkle_proof # contains all other infomration to verify a leaf at a certain position. # Namely the leaf value, the leaf position, the proof of that leaf's # position verify_merkle_proof(merkle_proof) sys.exit(0)

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