Adding Secure Lock to lock the device with a random 256 bit key.

This is an extra layer of security to avoid brute force attacks if PIN is too weak.
At every hard reset (on device plug), the device must be unlocked prior any other command. Once unlocked, the device can be used as usual.

Signed-off-by: Pol Henarejos <pol.henarejos@cttc.es>

tools/pico-hsm-tool.py

@@ -33,10 +33,22 @@ try:
     from cvc.oid import oid2scheme
     from cvc.utils import scheme_rsa
     from cvc.certificates import CVC
-    from cryptography.hazmat.primitives.asymmetric import ec
+
 except:
     print('ERROR: cvc module not found! Install pycvc package.\nTry with `pip install pycvc`')
     sys.exit(-1)
+
+try:
+    from cryptography.hazmat.primitives.asymmetric import ec
+    from cryptography.hazmat.primitives.kdf.hkdf import HKDF
+    from cryptography.hazmat.primitives.serialization import Encoding, PublicFormat
+    from cryptography.hazmat.primitives.ciphers.aead import ChaCha20Poly1305
+    from cryptography.hazmat.primitives import hashes
+except:
+    print('ERROR: cryptography module not found! Install cryptography package.\nTry with `pip install cryptography`')
+    sys.exit(-1)
+
+
 import json
 import urllib.request
 import base64
@@ -44,9 +56,20 @@ from binascii import hexlify
 import sys
 import argparse
 import os
+import platform
 from datetime import datetime
 from argparse import RawTextHelpFormatter
 
+if (platform.system() == 'Windows'):
+    from secure_key import windows as skey
+elif (platform.system() == 'Linux'):
+    from secure_key import linux as skey
+elif (platform.system() == 'Darwin'):
+    from secure_key import macos as skey
+else:
+    print('ERROR: platform not supported')
+    sys.exit(-1)
+
 class APDUResponse(Exception):
     def __init__(self, sw1, sw2):
         self.sw1 = sw1
@@ -98,6 +121,9 @@ def parse_args():
     parser_opts.add_argument('opt', choices=['button', 'counter'], help='Button: press-to-confirm button.\nCounter: every generated key has an internal counter.')
     parser_opts.add_argument('onoff', choices=['on', 'off'], help='Toggles state ON or OFF', metavar='ON/OFF', nargs='?')
 
+    parser_secure = subparser.add_parser('secure', help='Manages security of Pico Fido.')
+    parser_secure.add_argument('subcommand', choices=['enable', 'disable', 'unlock'], help='Enables, disables or unlocks the security.')
+
     args = parser.parse_args()
     return args
 
@@ -276,8 +302,68 @@ def opts(card, args):
     elif (args.subcommand == 'get'):
         print(f'Option {args.opt.upper()} is {"ON" if current & opt else "OFF"}')
 
+class SecureLock:
+    def __init__(self, card):
+        self.card = card
+
+    def mse(self):
+        sk = ec.generate_private_key(ec.SECP256R1())
+        pn = sk.public_key().public_numbers()
+        self.__pb = sk.public_key().public_bytes(Encoding.X962, PublicFormat.UncompressedPoint)
+
+
+        ret = send_apdu(self.card, [0x80, 0x64], 0x3A, 0x01, list(self.__pb))
+
+        pk = ec.EllipticCurvePublicKey.from_encoded_point(ec.SECP256R1(), bytes(ret))
+        shared_key = sk.exchange(ec.ECDH(), pk)
+
+        xkdf = HKDF(
+            algorithm=hashes.SHA256(),
+            length=12+32,
+            salt=None,
+            info=self.__pb
+        )
+        kdf_out = xkdf.derive(shared_key)
+        self.__key_enc = kdf_out[12:]
+        self.__iv = kdf_out[:12]
+
+    def encrypt_chacha(self, data):
+        chacha = ChaCha20Poly1305(self.__key_enc)
+        ct = chacha.encrypt(self.__iv, data, self.__pb)
+        return ct
+
+    def unlock_device(self):
+        ct = self.get_skey()
+        send_apdu(self.card, [0x80, 0x64], 0x3A, 0x03, list(ct))
+
+    def _get_key_device(self):
+        return skey.get_secure_key()
+
+    def get_skey(self):
+        self.mse()
+        ct = self.encrypt_chacha(self._get_key_device())
+        return ct
+
+    def enable_device_aut(self):
+        ct = self.get_skey()
+        send_apdu(self.card, [0x80, 0x64], 0x3A, 0x02, list(ct))
+
+    def disable_device_aut(self):
+        ct = self.get_skey()
+        send_apdu(self.card, [0x80, 0x64], 0x3A, 0x04, list(ct))
+
+
+def secure(card, args):
+    slck = SecureLock(card)
+    if (args.subcommand == 'enable'):
+        slck.enable_device_aut()
+    elif (args.subcommand == 'unlock'):
+        slck.unlock_device()
+    elif (args.subcommand == 'disable'):
+        slck.disable_device_aut()
+
 def main(args):
-    print('Pico HSM Tool v1.4')
+    print('Pico HSM Tool v1.6')
     print('Author: Pol Henarejos')
     print('Report bugs to https://github.com/polhenarejos/pico-hsm/issues')
     print('')
@@ -305,6 +391,8 @@ def main(args):
         rtc(card, args)
     elif (args.command == 'options'):
         opts(card, args)
+    elif (args.command == 'secure'):
+        secure(card, args)
 
 def run():
     args = parse_args()