esp-idf/tools/esp_prov/security/security2.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_security2
from typing import Any, Type
import proto
from cryptography.hazmat.primitives.ciphers.aead import AESGCM
from utils import long_to_bytes, str_to_bytes
from .security import Security
from .srp6a import Srp6a, generate_salt_and_verifier
AES_KEY_LEN = 256 // 8
# Enum for state of protocomm_security1 FSM
class security_state:
REQUEST1 = 0
RESPONSE1_REQUEST2 = 1
RESPONSE2 = 2
FINISHED = 3
def sec2_gen_salt_verifier(username: str, password: str, salt_len: int) -> Any:
salt, verifier = generate_salt_and_verifier(username, password, len_s=salt_len)
salt_str = ', '.join([format(b, '#04x') for b in salt])
salt_c_arr = '\n '.join(salt_str[i: i + 96] for i in range(0, len(salt_str), 96))
print(f'static const char sec2_salt[] = {{\n {salt_c_arr}\n}};\n')
verifier_str = ', '.join([format(b, '#04x') for b in verifier])
verifier_c_arr = '\n '.join(verifier_str[i: i + 96] for i in range(0, len(verifier_str), 96))
print(f'static const char sec2_verifier[] = {{\n {verifier_c_arr}\n}};\n')
class Security2(Security):
def __init__(self, username: str, password: str, verbose: bool) -> None:
# Initialize state of the security2 FSM
self.session_state = security_state.REQUEST1
self.username = username
self.password = password
self.verbose = verbose
self.srp6a_ctx: Type[Srp6a]
self.cipher: Type[AESGCM]
self.client_pop_key = None
self.nonce = None
Security.__init__(self, self.security2_session)
def security2_session(self, response_data: bytes) -> Any:
# protocomm security2 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()
if (self.session_state == security_state.RESPONSE1_REQUEST2):
self.session_state = security_state.RESPONSE2
self.setup0_response(response_data)
return self.setup1_request()
if (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 _print_verbose(self, data: str) -> None:
if (self.verbose):
print(f'\x1b[32;20m++++ {data} ++++\x1b[0m')
def setup0_request(self) -> Any:
# Form SessionCmd0 request packet using client public key
setup_req = proto.session_pb2.SessionData()
setup_req.sec_ver = proto.session_pb2.SecScheme2
setup_req.sec2.msg = proto.sec2_pb2.S2Session_Command0
setup_req.sec2.sc0.client_username = str_to_bytes(self.username)
self.srp6a_ctx = Srp6a(self.username, self.password)
if self.srp6a_ctx is None:
raise RuntimeError('Failed to initialize SRP6a instance!')
client_pubkey = long_to_bytes(self.srp6a_ctx.A)
setup_req.sec2.sc0.client_pubkey = client_pubkey
self._print_verbose(f'Client Public Key:\t0x{client_pubkey.hex()}')
return setup_req.SerializeToString().decode('latin-1')
def setup0_response(self, response_data: bytes) -> None:
# Interpret SessionResp0 response packet
setup_resp = proto.session_pb2.SessionData()
setup_resp.ParseFromString(str_to_bytes(response_data))
self._print_verbose(f'Security version:\t{str(setup_resp.sec_ver)}')
if setup_resp.sec_ver != proto.session_pb2.SecScheme2:
raise RuntimeError('Incorrect security scheme')
# Device public key, random salt and password verifier
device_pubkey = setup_resp.sec2.sr0.device_pubkey
device_salt = setup_resp.sec2.sr0.device_salt
self._print_verbose(f'Device Public Key:\t0x{device_pubkey.hex()}')
self.client_pop_key = self.srp6a_ctx.process_challenge(device_salt, device_pubkey)
def setup1_request(self) -> Any:
# Form SessionCmd1 request packet using encrypted device public key
setup_req = proto.session_pb2.SessionData()
setup_req.sec_ver = proto.session_pb2.SecScheme2
setup_req.sec2.msg = proto.sec2_pb2.S2Session_Command1
# Encrypt device public key and attach to the request packet
if self.client_pop_key is None:
raise RuntimeError('Failed to generate client proof!')
self._print_verbose(f'Client Proof:\t0x{self.client_pop_key.hex()}')
setup_req.sec2.sc1.client_proof = self.client_pop_key
return setup_req.SerializeToString().decode('latin-1')
def setup1_response(self, response_data: bytes) -> Any:
# 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.SecScheme2:
# Read encrypyed device proof string
device_proof = setup_resp.sec2.sr1.device_proof
self._print_verbose(f'Device Proof:\t0x{device_proof.hex()}')
self.srp6a_ctx.verify_session(device_proof)
if not self.srp6a_ctx.authenticated():
raise RuntimeError('Failed to verify device proof')
else:
raise RuntimeError('Unsupported security protocol')
# Getting the shared secret
shared_secret = self.srp6a_ctx.get_session_key()
self._print_verbose(f'Shared Secret:\t0x{shared_secret.hex()}')
# Using the first 256 bits of a 512 bit key
session_key = shared_secret[:AES_KEY_LEN]
self._print_verbose(f'Session Key:\t0x{session_key.hex()}')
# 96-bit nonce
self.nonce = setup_resp.sec2.sr1.device_nonce
if self.nonce is None:
raise RuntimeError('Received invalid nonce from device!')
self._print_verbose(f'Nonce:\t0x{self.nonce.hex()}')
# Initialize the encryption engine with Shared Key and initialization vector
self.cipher = AESGCM(session_key)
if self.cipher is None:
raise RuntimeError('Failed to initialize AES-GCM cryptographic engine!')
def encrypt_data(self, data: bytes) -> Any:
return self.cipher.encrypt(self.nonce, data, None)
def decrypt_data(self, data: bytes) -> Any:
return self.cipher.decrypt(self.nonce, data, None)