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from hashlib import blake2s
import binascii
def hash(x): return blake2s(x).digest()
zerohashes = [b'\x00' * 32]
for i in range(1, 32):
zerohashes.append(hash(zerohashes[i-1] + zerohashes[i-1]))
# Add a value to a Merkle tree by using the algo
# that stores a branch of sub-roots
def add_value(branch, index, value):
i = 0
while (index+1) % 2**(i+1) == 0:
i += 1
for j in range(0, i):
value = hash(branch[j] + value)
# branch[j] = zerohashes[j]
branch[i] = value
# Compute a Merkle root the dumb way
def merkle_root(values):
for h in range(32):
if len(values) % 2 == 1:
values.append(zerohashes[h])
values = [hash(values[i] + values[i+1]) for i in range(0, len(values), 2)]
return values[0]
def get_root_from_branch(branch, size):
r = b'\x00' * 32
for h in range(32):
if (size >> h) % 2 == 1:
r = hash(branch[h] + r)
else:
r = hash(r + zerohashes[h])
return r
def branch_by_branch(values):
branch = zerohashes[::]
# Construct the tree using the branch-based algo
for index, value in enumerate(values):
add_value(branch, index, value)
# Return the root
return get_root_from_branch(branch, len(values))
testdata = [(i + 2**255).to_bytes(32, 'big') for i in range(10000)]
# The Merkle root algo assumes trailing zero bytes
assert merkle_root(testdata[:5]) == merkle_root(testdata[:5] + [b'\x00' * 32] * 5)
# Verify equivalence of the simple all-at-once method and the progressive method
assert branch_by_branch(testdata[:1]) == merkle_root(testdata[:1])
assert branch_by_branch(testdata[:2]) == merkle_root(testdata[:2])
assert branch_by_branch(testdata[:3]) == merkle_root(testdata[:3])
assert branch_by_branch(testdata[:5049]) == merkle_root(testdata[:5049])
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