def _create_api_input(input_address: int,
input_note: api.ZethNote) -> api.JoinsplitInput:
mk_path = compute_merkle_path(input_address, mk_tree)
input_nullifier = compute_nullifier(input_note, sender_ask)
return create_api_joinsplit_input(mk_path, input_address,
input_note, sender_ask,
input_nullifier)
def _check_path_for_num_entries(num_entries: int,
address: int) -> None:
mktree = MerkleTree.empty_with_size(tree_size, MERKLE_TREE_HASH)
for val in TEST_VALUES[0:num_entries]:
mktree.insert(val)
_ = mktree.recompute_root()
mkpath = compute_merkle_path(address, mktree)
self._check_merkle_path(address, mkpath, mktree)
def charlie_double_withdraw(
zeth_client: MixerClient,
mk_tree: MerkleTree,
input1: Tuple[int, ZethNote],
charlie_eth_address: str,
keystore: mock.KeyStore) -> contracts.MixResult:
"""
Charlie tries to carry out a double spending by modifying the value of the
nullifier of the previous payment
"""
print(
f" === Charlie attempts to withdraw {CHARLIE_WITHDRAW_ETH}ETH once " +
"more (double spend) one of his note on the Mixer ===")
charlie_apk = keystore["Charlie"].addr_pk.a_pk
charlie_ask = keystore["Charlie"].addr_sk.a_sk
tree_depth = mk_tree.depth
mk_path1 = compute_merkle_path(input1[0], mk_tree)
mk_root = mk_tree.get_root()
# Create the an additional dummy input for the MixerClient
input2 = get_dummy_input_and_address(charlie_apk)
dummy_mk_path = mock.get_dummy_merkle_path(tree_depth)
note1_value = to_zeth_units(EtherValue(CHARLIE_WITHDRAW_CHANGE_ETH))
v_out = EtherValue(CHARLIE_WITHDRAW_ETH)
# ### ATTACK BLOCK
# Add malicious nullifiers: we reuse old nullifiers to double spend by
# adding $r$ to them so that they have the same value as before in Z_r,
# and so the zksnark verification passes, but have different values in
# {0;1}^256 so that they appear different to the contract.
# See: https://github.com/clearmatics/zeth/issues/38
attack_primary_input3: int = 0
attack_primary_input4: int = 0
def compute_h_sig_attack_nf(
nf0: bytes,
nf1: bytes,
sign_vk: JoinsplitSigVerificationKey) -> bytes:
# We disassemble the nfs to get the formatting of the primary inputs
input_nullifier0 = nf0.hex()
input_nullifier1 = nf1.hex()
nf0_rev = "{0:0256b}".format(int(input_nullifier0, 16))
primary_input3_bits = nf0_rev[:FIELD_CAPACITY]
primary_input3_res_bits = nf0_rev[FIELD_CAPACITY:]
nf1_rev = "{0:0256b}".format(int(input_nullifier1, 16))
primary_input4_bits = nf1_rev[:FIELD_CAPACITY]
primary_input4_res_bits = nf1_rev[FIELD_CAPACITY:]
# We perform the attack, recoding the modified public input values
nonlocal attack_primary_input3
nonlocal attack_primary_input4
attack_primary_input3 = int(primary_input3_bits, 2) + ZETH_PRIME
attack_primary_input4 = int(primary_input4_bits, 2) + ZETH_PRIME
# We reassemble the nfs
attack_primary_input3_bits = "{0:0256b}".format(attack_primary_input3)
attack_nf0_bits = attack_primary_input3_bits[
len(attack_primary_input3_bits) - FIELD_CAPACITY:] +\
primary_input3_res_bits
attack_nf0 = "{0:064x}".format(int(attack_nf0_bits, 2))
attack_primary_input4_bits = "{0:0256b}".format(attack_primary_input4)
attack_nf1_bits = attack_primary_input4_bits[
len(attack_primary_input4_bits) - FIELD_CAPACITY:] +\
primary_input4_res_bits
attack_nf1 = "{0:064x}".format(int(attack_nf1_bits, 2))
return compute_h_sig(
bytes.fromhex(attack_nf0), bytes.fromhex(attack_nf1), sign_vk)
(output_note1, output_note2, proof_json, signing_keypair) = \
zeth_client.get_proof_joinsplit_2_by_2(
mk_root,
input1,
mk_path1,
input2,
dummy_mk_path,
charlie_ask, # sender
(charlie_apk, note1_value), # recipient1
(charlie_apk, 0), # recipient2
to_zeth_units(EtherValue(0)), # v_in
to_zeth_units(v_out), # v_out
compute_h_sig_attack_nf)
# Update the primary inputs to the modified nullifiers, since libsnark
# overwrites them with values in Z_p
assert attack_primary_input3 != 0
assert attack_primary_input4 != 0
print("proof_json => ", proof_json)
print("proof_json[inputs][3] => ", proof_json["inputs"][3])
print("proof_json[inputs][4] => ", proof_json["inputs"][4])
proof_json["inputs"][3] = hex(attack_primary_input3)
proof_json["inputs"][4] = hex(attack_primary_input4)
# ### ATTACK BLOCK
# construct pk object from bytes
pk_charlie = keystore["Charlie"].addr_pk.k_pk
# encrypt the coins
ciphertexts = encrypt_notes([
(output_note1, pk_charlie),
(output_note2, pk_charlie)])
# Compute the joinSplit signature
joinsplit_sig_charlie = joinsplit_sign(
signing_keypair,
charlie_eth_address,
ciphertexts,
proof_json)
mix_params = contracts.MixParameters(
proof_json,
signing_keypair.vk,
joinsplit_sig_charlie,
ciphertexts)
tx_hash = zeth_client.mix(
mix_params,
charlie_eth_address,
# Pay an arbitrary amount (1 wei here) that will be refunded since the
# `mix` function is payable
None,
EtherValue(1, 'wei'))
return wait_for_tx_update_mk_tree(zeth_client, mk_tree, tx_hash)
def create_prover_inputs(
mix_call_desc: MixCallDescription
) -> Tuple[ProofInputs, signing.SigningKeyPair]:
"""
Given the basic parameters for a mix call, compute the input to the prover
server, and the signing key pair.
"""
# Compute Merkle paths
mk_tree = mix_call_desc.mk_tree
mk_root = mk_tree.get_root()
inputs = mix_call_desc.inputs
mk_paths = [compute_merkle_path(addr, mk_tree) for addr, _ in inputs]
# Extract (<ownership-address>, <value>) tuples
outputs_with_a_pk = \
[(zeth_addr.a_pk, to_zeth_units(value))
for (zeth_addr, value) in mix_call_desc.outputs]
output0 = outputs_with_a_pk[0]
output1 = outputs_with_a_pk[1]
# Public input and output values as Zeth units
public_in_value_zeth_units = to_zeth_units(mix_call_desc.v_in)
public_out_value_zeth_units = to_zeth_units(mix_call_desc.v_out)
# Generate the signing key
signing_keypair = signing.gen_signing_keypair()
sender_ask = mix_call_desc.sender_ownership_keypair.a_sk
# Compute the input note nullifiers
(input_address0, input_note0) = mix_call_desc.inputs[0]
(input_address1, input_note1) = mix_call_desc.inputs[1]
input_nullifier0 = compute_nullifier(input_note0, sender_ask)
input_nullifier1 = compute_nullifier(input_note1, sender_ask)
# Convert to JoinsplitInput objects
js_inputs: List[JoinsplitInput] = [
create_joinsplit_input(mk_paths[0], input_address0, input_note0,
sender_ask, input_nullifier0),
create_joinsplit_input(mk_paths[1], input_address1, input_note1,
sender_ask, input_nullifier1)
]
# Use the specified or default h_sig computation
compute_h_sig_cb = mix_call_desc.compute_h_sig_cb or compute_h_sig
h_sig = compute_h_sig_cb(input_nullifier0, input_nullifier1,
signing_keypair.vk)
phi = _phi_randomness()
# Joinsplit Output Notes
output_note0, output_note1 = _create_zeth_notes(
phi, h_sig, output0, output1)
js_outputs = [output_note0, output_note1]
proof_inputs = ProofInputs(
mk_root=mk_root.hex(),
js_inputs=js_inputs,
js_outputs=js_outputs,
pub_in_value=int64_to_hex(public_in_value_zeth_units),
pub_out_value=int64_to_hex(public_out_value_zeth_units),
h_sig=h_sig.hex(),
phi=phi.hex())
return (proof_inputs, signing_keypair)
def create_mix_parameters_keep_signing_key(
self,
mk_tree: MerkleTree,
sender_ownership_keypair: OwnershipKeyPair,
sender_eth_address: str,
inputs: List[Tuple[int, ZethNote]],
outputs: List[Tuple[ZethAddressPub, EtherValue]],
v_in: EtherValue,
v_out: EtherValue,
compute_h_sig_cb: Optional[ComputeHSigCB] = None
) -> Tuple[contracts.MixParameters, JoinsplitSigKeyPair]:
assert len(inputs) <= constants.JS_INPUTS
assert len(outputs) <= constants.JS_OUTPUTS
sender_a_sk = sender_ownership_keypair.a_sk
sender_a_pk = sender_ownership_keypair.a_pk
inputs = \
inputs + \
[get_dummy_input_and_address(sender_a_pk)
for _ in range(constants.JS_INPUTS - len(inputs))]
mk_root = mk_tree.get_root()
mk_paths = [compute_merkle_path(addr, mk_tree) for addr, _ in inputs]
# Generate output notes and proof. Dummy outputs are constructed with
# value 0 to an invalid ZethAddressPub, formed from the senders
# a_pk, and an ephemeral k_pk.
dummy_k_pk = generate_encryption_keypair().k_pk
dummy_addr_pk = ZethAddressPub(sender_a_pk, dummy_k_pk)
outputs = \
outputs + \
[(dummy_addr_pk, EtherValue(0))
for _ in range(constants.JS_OUTPUTS - len(outputs))]
outputs_with_a_pk = \
[(zeth_addr.a_pk, to_zeth_units(value))
for (zeth_addr, value) in outputs]
# Timer used to time proof-generation round trip time.
timer = Timer.started()
(output_note1, output_note2, extproof, signing_keypair) = \
self.get_proof_joinsplit_2_by_2(
mk_root,
inputs[0],
mk_paths[0],
inputs[1],
mk_paths[1],
sender_a_sk,
outputs_with_a_pk[0],
outputs_with_a_pk[1],
to_zeth_units(v_in),
to_zeth_units(v_out),
compute_h_sig_cb)
proof_gen_time_s = timer.elapsed_seconds()
print(f"PROOF GEN ROUND TRIP: {proof_gen_time_s} seconds")
# Encrypt the notes
outputs_and_notes = zip(outputs, [output_note1, output_note2])
output_notes_with_k_pk = \
[(note, zeth_addr.k_pk)
for ((zeth_addr, _), note) in outputs_and_notes]
ciphertexts = encrypt_notes(output_notes_with_k_pk)
# Sign
signature = joinsplit_sign(signing_keypair, sender_eth_address,
ciphertexts, extproof)
mix_params = contracts.MixParameters(extproof, signing_keypair.vk,
signature, ciphertexts)
return mix_params, signing_keypair