def perform(shard, leaves, seed, size=0, offset=0):
response = store.shard.get_hash_hex(shard, hex_salt=seed,
size=size, offset=offset)
leaf = util.hash_hex(response)
assert(leaf in leaves)
challengenum = leaves.index(leaf)
width = util.next_power_of_two(len(leaves))
proof = leaves + [util.hash_hex("") for x in range(width - len(leaves))]
proof[challengenum] = [response]
return trim(proof, challengenum)
def prepare(shard, challenges):
# very inefficient implementation
leaves = []
for challenge in challenges:
response = store.shard.get_hash_hex(shard, hex_salt=challenge["seed"],
size=challenge["size"],
offset=challenge["offset"])
leaves.append(util.hash_hex(response))
return leaves
def collapse(proof, leaf, depth):
""" Collapse and validate the proof for the given leaf.
Args:
proof: The merkle proof to collapse.
leaf: The leaf the given proof is for.
depth: The reqired depth of the proof.
Returns:
The merkle root if the proof is valid.
Raises:
AssertionError: If incorrect proof or incorrect proof format.
"""
if depth == 0:
assert(len(proof) == 1) # contains only the challenge response
assert(util.is_hex_hash(proof[0]))
assert(util.hash_hex(proof[0]) == leaf) # response for expected leaf
return leaf
assert(len(proof) == 2)
# collapse left branch
if isinstance(proof[0], list):
hashl = collapse(proof[0], leaf, depth - 1)
else:
assert(util.is_hex_hash(proof[0]))
hashl = proof[0] # end of branch
# collapse right branch
if isinstance(proof[1], list):
hashr = collapse(proof[1], leaf, depth - 1)
else:
assert(util.is_hex_hash(proof[1]))
hashr = proof[1] # end of branch
return util.hash_hex(hashl + hashr)
def trim(proof, index):
""" Trim branches not leading to proof.
Args:
proof: The proof to be trimmed.
index: Index of the branch to preserve, others are trimmed.
Returns:
The trimmed proof.
"""
if len(proof) == 2:
return proof
proof = util.chunks(proof, 2)
proof_next = []
for branch_index, branch in enumerate(proof):
if branch_index != index / 2: # trim branch not leading to response
proof_next.append(util.hash_hex(branch[0] + branch[1]))
else:
proof_next.append(branch)
return trim(proof_next, index / 2) # FIXME check it floors division!!!
