esp-idf/tools/esp_prov/security/security1.py

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