def test_chain(self):
G = Block.genesis()
C = Chain()
C.append(G)
b = C.mine()
self.assertEqual(len(C), 2)
self.assertEqual(C[0], G)
self.assertEqual(C[-1], b)
self.assertEqual(C[0:2], C)
self.assertEqual(len(C.slice(G, b)), 1)
self.assertEqual(C[0].height, 0)
self.assertEqual(C[1].height, 1)
self.assertTrue(C.is_chained())
class Adversary(Party):
def __init__(self, genesis, k, m, mu_B):
self.attack_phase = AttackPhase.DOUBLE_SPEND
self.m = m
self.k = k
self.mu_B = mu_B
self.bypass_level = mu_B
self.bypass_level_blocks_seen = 0
self.min_bypass_level = 2
self.honest_chain = Chain(genesis)
self.last_good_honest_block = None
self.double_spend_block = None
self.stitch_block = None
self.blocks_mined = []
self.need_bypass = False
self.adversarial_nipopow = NIPoPoW(k, m)
self.adversarial_nipopow.chain.append(genesis)
super().__init__(genesis)
def play(self):
if self.attack_phase == AttackPhase.DOUBLE_SPEND:
self.double_spend_block = self.chain.mine(True)
self.blocks_mined.append(self.double_spend_block)
self.adversarial_nipopow.chain.append(self.double_spend_block)
self.attack_phase = AttackPhase.STITCH
return None # withhold double spending block
if self.attack_phase == AttackPhase.STITCH:
self.stitch_block = self.honest_chain.mine(True)
self.stitch_block.set_thorny_interlink([self.double_spend_block])
self.last_good_honest_block = self.stitch_block
self.blocks_mined.append(self.stitch_block)
self.adversarial_nipopow.chain.append(self.stitch_block)
self.attack_phase = AttackPhase.GROW
return self.honest_chain
if self.attack_phase == AttackPhase.GROW:
# discard = True
if self.need_bypass:
b = Block.mine(self.honest_chain[-1])
b.adversarial = True
b.set_thorny_interlink([self.last_good_honest_block])
self.blocks_mined.append(b)
if b.level < self.bypass_level:
# Our block is of low enough level to stay under the radar
# so we can use it for bypassing
# Bypass any blocks between last_good_honest_block and b,
# as they are blocks of a higher level than what we want.
self.last_good_honest_block = b
self.honest_chain.append(b)
self.adversarial_nipopow.chain.append(b)
# Bypass was successful.
self.need_bypass = False
# discard = False
return self.honest_chain
else:
# Unfortunately, we mined a block of high level and this
# cannot be used for bypassing (as b would then be included
# by the honest prover into their proof), so we have to discard
# this block and try again
# discard = True
pass
# if not discard:
# return b
if self.attack_phase == AttackPhase.SUFFIX:
b = self.chain.mine(True)
self.blocks_mined.append(b)
self.adversarial_nipopow.chain.append(b)
self.suffix_size += 1
if self.suffix_size >= k and self.growth_completed():
self.attack_phase = AttackPhase.DONE
return None # withhold suffix
def block_arrival(self, chain):
block = chain[-1]
if self.attack_phase > AttackPhase.STITCH and self.attack_phase < AttackPhase.SUFFIX:
if block.level >= self.bypass_level:
# A superblock has appeared which is of higher level than we want.
# We need to bypass it.
# (There could be multiple of these in a row)
self.need_bypass = True
self.bypass_level_blocks_seen += 1
if self.bypass_level_blocks_seen >= m:
self.bypass_level -= 1
self.bypass_level_blocks_seen = 0
if self.bypass_level < self.min_bypass_level:
self.attack_phase = AttackPhase.SUFFIX
self.chain = Chain(self.last_good_honest_block)
self.suffix_size = 0
else:
if not self.need_bypass:
self.last_good_honest_block = block
self.adversarial_nipopow.chain.append(block)
self.honest_chain = chain
def growth_completed(self):
m = self.m
mu_B = self.mu_B
C = self.honest_chain.slice(self.stitch_block)
if C.count_upchain(mu_B) < 2 * m:
return False
b = C[0]
for mu in range(mu_B - 1, 0, -1):
b = C.upchain(mu + 1)[m]
C = C.slice(b)
if C.count_upchain(mu) < 2 * m:
return False
return True
def ready(self):
return self.attack_phase == AttackPhase.DONE