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from typing import List, Set, Type
from warnings import catch_warnings
from doubleratchet import (
DoSProtectionException,
DuplicateMessageException
)
from doubleratchet.diffie_hellman_ratchet import DiffieHellmanRatchet
from doubleratchet.recommended import (
diffie_hellman_ratchet_curve25519 as dhr25519,
diffie_hellman_ratchet_curve448 as dhr448,
HashFunction,
kdf_hkdf
)
from .test_recommended_kdfs import generate_unique_random_data
__all__ = [
"test_diffie_hellman_ratchet"
]
try:
import pytest
except ImportError:
pass
else:
pytestmark = pytest.mark.asyncio
class RootChainKDF(kdf_hkdf.KDF):
"""
The root chain KDF to use for testing.
"""
@staticmethod
def _get_hash_function() -> HashFunction:
return HashFunction.SHA_512
@staticmethod
def _get_info() -> bytes:
return "test_diffie_hellman_ratchet Root Chain info".encode("ASCII")
class MessageChainKDF(kdf_hkdf.KDF):
"""
The message chain KDF to use for testing.
"""
@staticmethod
def _get_hash_function() -> HashFunction:
return HashFunction.SHA_512_256
@staticmethod
def _get_info() -> bytes:
return "test_diffie_hellman_ratchet Message Chain info".encode("ASCII")
async def test_diffie_hellman_ratchet() -> None:
"""
Test the Diffie-Hellman ratchet implementation.
"""
# pylint: disable=protected-access
impls: List[Type[DiffieHellmanRatchet]] = [ dhr25519.DiffieHellmanRatchet, dhr448.DiffieHellmanRatchet ]
for impl in impls:
root_chain_key_set: Set[bytes] = set()
message_chain_constant_set: Set[bytes] = set()
for _ in range(100):
# Generate random parameters
root_chain_key = generate_unique_random_data(32, 32 + 1, root_chain_key_set)
message_chain_constant = generate_unique_random_data(0, 2 ** 16, message_chain_constant_set)
bob_priv = impl._generate_priv()
# Create instances for Alice and Bob and exchange an initial message
alice_dhr = await impl.create(
None,
impl._derive_pub(bob_priv),
RootChainKDF,
root_chain_key,
MessageChainKDF,
message_chain_constant,
10
)
encryption_key, header = await alice_dhr.next_encryption_key()
bob_dhr = await impl.create(
bob_priv,
header.ratchet_pub,
RootChainKDF,
root_chain_key,
MessageChainKDF,
message_chain_constant,
10
)
decryption_key, skipped_message_keys = await bob_dhr.next_decryption_key(header)
assert header.previous_sending_chain_length == 0
assert header.sending_chain_length == 0
assert len(skipped_message_keys) == 0
assert len(encryption_key) == len(decryption_key) == 32
assert encryption_key == decryption_key
alice_pub = header.ratchet_pub
# Test that Bob can send to Alice now
encryption_key, header = await bob_dhr.next_encryption_key()
decryption_key, skipped_message_keys = await alice_dhr.next_decryption_key(header)
assert header.previous_sending_chain_length == 0
assert header.sending_chain_length == 0
assert len(skipped_message_keys) == 0
assert len(encryption_key) == len(decryption_key) == 32
assert encryption_key == decryption_key
assert header.ratchet_pub != impl._derive_pub(bob_priv)
bob_pub = header.ratchet_pub
# Test that n increases in the header and the ratchet pub stays the same
encryption_key, header = await bob_dhr.next_encryption_key()
decryption_key, skipped_message_keys = await alice_dhr.next_decryption_key(header)
assert header.previous_sending_chain_length == 0
assert header.sending_chain_length == 1
assert len(skipped_message_keys) == 0
assert len(encryption_key) == len(decryption_key) == 32
assert encryption_key == decryption_key
assert header.ratchet_pub == bob_pub
bob_pub = header.ratchet_pub
# Test that switching sender/receiver triggers a Diffie-Hellman ratchet step
encryption_key, header = await alice_dhr.next_encryption_key()
decryption_key, skipped_message_keys = await bob_dhr.next_decryption_key(header)
assert header.previous_sending_chain_length == 1
assert header.sending_chain_length == 0
assert len(skipped_message_keys) == 0
assert len(encryption_key) == len(decryption_key) == 32
assert encryption_key == decryption_key
assert header.ratchet_pub != alice_pub
alice_pub = header.ratchet_pub
# Test that pn is set correctly in the header
encryption_key, header = await bob_dhr.next_encryption_key()
decryption_key, skipped_message_keys = await alice_dhr.next_decryption_key(header)
assert header.previous_sending_chain_length == 2
assert header.sending_chain_length == 0
assert len(skipped_message_keys) == 0
assert len(encryption_key) == len(decryption_key) == 32
assert encryption_key == decryption_key
assert header.ratchet_pub != bob_pub
bob_pub = header.ratchet_pub
# Test a few skipped messages (simple case, no Diffie-Hellman ratchet steps)
skipped_encryption_key_1, skipped_header_1 = await bob_dhr.next_encryption_key()
skipped_encryption_key_2, skipped_header_2 = await bob_dhr.next_encryption_key()
skipped_encryption_key_3, skipped_header_3 = await bob_dhr.next_encryption_key()
encryption_key, header = await bob_dhr.next_encryption_key()
decryption_key, skipped_message_keys = await alice_dhr.next_decryption_key(header)
assert header.previous_sending_chain_length == 2
assert header.sending_chain_length == 4
assert len(skipped_message_keys) == 3
assert len(encryption_key) == len(decryption_key) == 32
assert encryption_key == decryption_key
assert header.ratchet_pub == bob_pub
bob_pub = header.ratchet_pub
# Check the skipped message keys
assert skipped_header_1.ratchet_pub == bob_pub
assert skipped_header_2.ratchet_pub == bob_pub
assert skipped_header_3.ratchet_pub == bob_pub
assert skipped_header_1.previous_sending_chain_length == 2
assert skipped_header_2.previous_sending_chain_length == 2
assert skipped_header_3.previous_sending_chain_length == 2
assert skipped_header_1.sending_chain_length == 1
assert skipped_header_2.sending_chain_length == 2
assert skipped_header_3.sending_chain_length == 3
assert skipped_message_keys[(bob_pub, 1)] == skipped_encryption_key_1
assert skipped_message_keys[(bob_pub, 2)] == skipped_encryption_key_2
assert skipped_message_keys[(bob_pub, 3)] == skipped_encryption_key_3
# Test that attempting to acquire one of these keys again raises an exception
try:
await alice_dhr.next_decryption_key(skipped_header_3)
assert False
except DuplicateMessageException:
pass
try:
await alice_dhr.next_decryption_key(header)
assert False
except DuplicateMessageException:
pass
# Test the more complicated case of skipped message keys (after a Diffie-Hellman ratchet step)
skipped_encryption_key, skipped_header = await bob_dhr.next_encryption_key() # Prepare a message
encryption_key, header = await alice_dhr.next_encryption_key() # Perform a DH ratchet step
decryption_key, skipped_message_keys = await bob_dhr.next_decryption_key(header)
encryption_key, header = await bob_dhr.next_encryption_key() # Let Alice decrypt a fresh message
decryption_key, skipped_message_keys = await alice_dhr.next_decryption_key(header)
assert len(encryption_key) == len(decryption_key) == 32
assert encryption_key == decryption_key
assert len(skipped_message_keys) == 1
skipped_message_keys_key = (skipped_header.ratchet_pub, skipped_header.sending_chain_length)
assert skipped_message_keys[skipped_message_keys_key] == skipped_encryption_key
# Decrypting this message should not raise an exception but mess up the ratchet instead and return
# a wrong key:
decryption_key, skipped_message_keys = await alice_dhr.next_decryption_key(skipped_header)
assert decryption_key != skipped_encryption_key
# The ratchets are now completely desynchronized, the only option is creating new ratchets. The
# Double Ratchet mitigates this issue.
alice_dhr = await impl.create(
None,
impl._derive_pub(bob_priv),
RootChainKDF,
root_chain_key,
MessageChainKDF,
message_chain_constant,
10
)
encryption_key, header = await alice_dhr.next_encryption_key()
bob_dhr = await impl.create(
bob_priv,
header.ratchet_pub,
RootChainKDF,
root_chain_key,
MessageChainKDF,
message_chain_constant,
10
)
decryption_key, skipped_message_keys = await bob_dhr.next_decryption_key(header)
assert header.previous_sending_chain_length == 0
assert header.sending_chain_length == 0
assert len(skipped_message_keys) == 0
assert len(encryption_key) == len(decryption_key) == 32
assert encryption_key == decryption_key
alice_pub = header.ratchet_pub
# Test the (hard) DoS protection by skipping more than 10 messages:
for _ in range(25):
await bob_dhr.next_encryption_key()
encryption_key, header = await bob_dhr.next_encryption_key()
try:
await alice_dhr.next_decryption_key(header)
assert False
except DoSProtectionException:
pass
# Perform a Diffie-Hellman ratchet step
encryption_key, header = await alice_dhr.next_encryption_key()
decryption_key, skipped_message_keys = await bob_dhr.next_decryption_key(header)
# Test the (soft) DoS protection:
encryption_key, header = await bob_dhr.next_encryption_key()
with catch_warnings(record=True) as warnings:
decryption_key, skipped_message_keys = await alice_dhr.next_decryption_key(header)
assert len(warnings) == 1
assert issubclass(warnings[0].category, UserWarning)
assert "DoS" in str(warnings[0].message)
assert len(skipped_message_keys) == 0 # Without DoS protection, this would be 25+
assert len(encryption_key) == len(decryption_key) == 32
assert encryption_key == decryption_key
# Make sure that a root key of a different size than 32 bytes is rejected
try:
await impl.create(
None,
impl._derive_pub(bob_priv),
RootChainKDF,
b"\00" * 64,
MessageChainKDF,
message_chain_constant,
10
)
assert False
except ValueError as e:
assert "key" in str(e)
assert "root chain" in str(e)
assert "32 bytes" in str(e)
# Test that (de)serializing doesn't influence the functionality
encryption_key, header = await alice_dhr.next_encryption_key()
decryption_key, skipped_message_keys = await bob_dhr.next_decryption_key(header)
assert encryption_key == decryption_key
alice_dhr = impl.from_json(alice_dhr.json, RootChainKDF, MessageChainKDF,
message_chain_constant, 10)
encryption_key, header = await alice_dhr.next_encryption_key()
decryption_key, skipped_message_keys = await bob_dhr.next_decryption_key(header)
assert encryption_key == decryption_key
bob_dhr = impl.from_json(bob_dhr.json, RootChainKDF, MessageChainKDF,
message_chain_constant, 10)
encryption_key, header = await alice_dhr.next_encryption_key()
decryption_key, skipped_message_keys = await bob_dhr.next_decryption_key(header)
assert encryption_key == decryption_key
# Make sure that a message can be decrypted twice by restoring an old serialized state
encryption_key, header = await alice_dhr.next_encryption_key()
bob_dhr_serialized = bob_dhr.json
decryption_key, skipped_message_keys = await bob_dhr.next_decryption_key(header)
assert encryption_key == decryption_key
bob_dhr = impl.from_json(bob_dhr_serialized, RootChainKDF, MessageChainKDF,
message_chain_constant, 10)
decryption_key, skipped_message_keys = await bob_dhr.next_decryption_key(header)
assert encryption_key == decryption_key
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