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146 lines
6.4 KiB
Python
146 lines
6.4 KiB
Python
# SPDX-FileCopyrightText: 2018-2022 Espressif Systems (Shanghai) CO LTD
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# SPDX-License-Identifier: Apache-2.0
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#
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# APIs for interpreting and creating protobuf packets for
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# protocomm endpoint with security type protocomm_security1
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import proto
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from cryptography.hazmat.backends import default_backend
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from cryptography.hazmat.primitives import hashes
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from cryptography.hazmat.primitives import serialization
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from cryptography.hazmat.primitives.asymmetric.x25519 import X25519PrivateKey
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from cryptography.hazmat.primitives.asymmetric.x25519 import X25519PublicKey
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from cryptography.hazmat.primitives.ciphers import Cipher
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from cryptography.hazmat.primitives.ciphers import algorithms
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from cryptography.hazmat.primitives.ciphers import modes
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from utils import long_to_bytes
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from utils import str_to_bytes
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from .security import Security
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def a_xor_b(a: bytes, b: bytes) -> bytes:
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return b''.join(long_to_bytes(a[i] ^ b[i]) for i in range(0, len(b)))
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# Enum for state of protocomm_security1 FSM
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class security_state:
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REQUEST1 = 0
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RESPONSE1_REQUEST2 = 1
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RESPONSE2 = 2
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FINISHED = 3
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class Security1(Security):
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def __init__(self, pop, verbose):
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# Initialize state of the security1 FSM
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self.session_state = security_state.REQUEST1
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self.pop = str_to_bytes(pop)
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self.verbose = verbose
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Security.__init__(self, self.security1_session)
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def security1_session(self, response_data):
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# protocomm security1 FSM which interprets/forms
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# protobuf packets according to present state of session
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if self.session_state == security_state.REQUEST1:
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self.session_state = security_state.RESPONSE1_REQUEST2
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return self.setup0_request()
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elif self.session_state == security_state.RESPONSE1_REQUEST2:
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self.session_state = security_state.RESPONSE2
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self.setup0_response(response_data)
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return self.setup1_request()
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elif self.session_state == security_state.RESPONSE2:
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self.session_state = security_state.FINISHED
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self.setup1_response(response_data)
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return None
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print('Unexpected state')
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return None
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def __generate_key(self):
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# Generate private and public key pair for client
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self.client_private_key = X25519PrivateKey.generate()
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self.client_public_key = self.client_private_key.public_key().public_bytes(
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encoding=serialization.Encoding.Raw, format=serialization.PublicFormat.Raw
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)
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def _print_verbose(self, data):
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if self.verbose:
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print(f'\x1b[32;20m++++ {data} ++++\x1b[0m')
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def setup0_request(self):
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# Form SessionCmd0 request packet using client public key
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setup_req = proto.session_pb2.SessionData()
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setup_req.sec_ver = proto.session_pb2.SecScheme1
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self.__generate_key()
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setup_req.sec1.sc0.client_pubkey = self.client_public_key
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self._print_verbose(f'Client Public Key:\t0x{self.client_public_key.hex()}')
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return setup_req.SerializeToString().decode('latin-1')
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def setup0_response(self, response_data):
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# Interpret SessionResp0 response packet
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setup_resp = proto.session_pb2.SessionData()
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setup_resp.ParseFromString(str_to_bytes(response_data))
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self._print_verbose('Security version:\t' + str(setup_resp.sec_ver))
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if setup_resp.sec_ver != proto.session_pb2.SecScheme1:
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raise RuntimeError('Incorrect security scheme')
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self.device_public_key = setup_resp.sec1.sr0.device_pubkey
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# Device random is the initialization vector
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device_random = setup_resp.sec1.sr0.device_random
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self._print_verbose(f'Device Public Key:\t0x{self.device_public_key.hex()}')
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self._print_verbose(f'Device Random:\t0x{device_random.hex()}')
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# Calculate Curve25519 shared key using Client private key and Device public key
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sharedK = self.client_private_key.exchange(X25519PublicKey.from_public_bytes(self.device_public_key))
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self._print_verbose(f'Shared Key:\t0x{sharedK.hex()}')
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# If PoP is provided, XOR SHA256 of PoP with the previously
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# calculated Shared Key to form the actual Shared Key
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if len(self.pop) > 0:
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# Calculate SHA256 of PoP
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h = hashes.Hash(hashes.SHA256(), backend=default_backend())
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h.update(self.pop)
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digest = h.finalize()
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# XOR with and update Shared Key
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sharedK = a_xor_b(sharedK, digest)
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self._print_verbose(f'Updated Shared Key (Shared key XORed with PoP):\t0x{sharedK.hex()}')
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# Initialize the encryption engine with Shared Key and initialization vector
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cipher = Cipher(algorithms.AES(sharedK), modes.CTR(device_random), backend=default_backend())
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self.cipher = cipher.encryptor()
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def setup1_request(self):
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# Form SessionCmd1 request packet using encrypted device public key
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setup_req = proto.session_pb2.SessionData()
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setup_req.sec_ver = proto.session_pb2.SecScheme1
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setup_req.sec1.msg = proto.sec1_pb2.Session_Command1
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# Encrypt device public key and attach to the request packet
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client_verify = self.cipher.update(self.device_public_key)
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self._print_verbose(f'Client Proof:\t0x{client_verify.hex()}')
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setup_req.sec1.sc1.client_verify_data = client_verify
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return setup_req.SerializeToString().decode('latin-1')
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def setup1_response(self, response_data):
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# Interpret SessionResp1 response packet
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setup_resp = proto.session_pb2.SessionData()
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setup_resp.ParseFromString(str_to_bytes(response_data))
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# Ensure security scheme matches
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if setup_resp.sec_ver == proto.session_pb2.SecScheme1:
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# Read encrypyed device verify string
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device_verify = setup_resp.sec1.sr1.device_verify_data
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self._print_verbose(f'Device Proof:\t0x{device_verify.hex()}')
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# Decrypt the device verify string
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enc_client_pubkey = self.cipher.update(setup_resp.sec1.sr1.device_verify_data)
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# Match decrypted string with client public key
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if enc_client_pubkey != self.client_public_key:
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raise RuntimeError('Failed to verify device!')
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else:
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raise RuntimeError('Unsupported security protocol')
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def encrypt_data(self, data):
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return self.cipher.update(data)
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def decrypt_data(self, data):
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return self.cipher.update(data)
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