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Protect main OTP against unauthed changes

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This is a problem if someone sends:

000000handshake xyz

...because they will have set our OTP to xyz and could guess codes.

Fixed by using a separate OTP object for handshaking only.
This commit is contained in:
Tanner Collin 2019-09-23 04:52:24 +00:00
parent 03e37f5601
commit 47ad8b575a
3 changed files with 42 additions and 32 deletions
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10
README.md
View File

@ -31,11 +31,10 @@ event.respond('000000handshake ' + bwb.handshake(data))
On `000000handshake [data]`:
```text
event.respond(bwb.wrap('secret ' + bwb.secret(data)))
bwb.set_otp(bwb.init_secret)
event.respond(bwb.wrap('secret ' + bwb.secret(data), handshake=True))
```
On _OTP authed_ `123456secret [data]`:
On _Handshake OTP authed_ `123456secret [data]`:
```text
bwb.set_secret(data)
@ -62,6 +61,9 @@ if text.startswith('!'):
...
elif text.startswith('000000'):
text = text[6:]
elif bwb.check_auth(text, handshake=True):
handshake_authed = True
text = text[6:]
elif bwb.check_auth(text):
authed = True
text = text[6:]
@ -74,7 +76,7 @@ Use `bwb.wrap()` to auth and encode outgoing commands.
Params:
```text
wrap(text, target=None, b58=False, enc=False)
wrap(text, handshake=False, target=None, b58=False, enc=False)
```
Examples:

62
bwb/common.py
View File

@ -20,21 +20,11 @@ from cryptography.hazmat.primitives.kdf.hkdf import HKDF
OTP_LOOKAHEAD = 25
class common:
def __init__(self):
self.init_secret = ''
self.key = None
self.master_pub = None
self.otp = None
self.otp_secret = ''
class OTP:
def __init__(self, secret):
self.otp = HOTP(secret.encode(), 6, SHA1(), backend=default_backend(), enforce_key_length=False)
self.otp_count = 0
def set_otp(self, otp_secret):
self.otp = HOTP(otp_secret.encode(), 6, SHA1(), backend=default_backend(), enforce_key_length=False)
self.otp_secret = otp_secret
self.otp_count = 0
return True
def get_otp(self, target):
if not self.otp:
raise RuntimeError('bwb not init yet')
@ -55,7 +45,7 @@ class common:
self.otp_count += 1
return code
def check_otp(self, code):
def check_otp(self, code, me):
if not self.otp:
return False
@ -65,11 +55,20 @@ class common:
if otp_at == str(code): # broadcast
self.otp_count = count + 1
return True
elif self.TELEGRAM_ID % int(otp_at) == int(code):
elif me % int(otp_at) == int(code):
self.otp_count = count + 1
return True
return False
class common:
def __init__(self):
self.key = None
self.master_pub = None
self.init_secret = ''
self.handshake_otp = None
self.enc_secret = ''
self.otp = None
def to_b58(self, text):
return 'l' + base58.b58encode(text.encode()).decode()
@ -83,7 +82,7 @@ class common:
def enc(self, text, key=None):
if not key:
key = self.otp_secret.encode()
key = self.enc_secret.encode()
if not key:
raise RuntimeError('bwb not init yet')
@ -105,7 +104,7 @@ class common:
def dec(self, ciphertext, key=None):
if not key:
key = self.otp_secret.encode()
key = self.enc_secret.encode()
if not key:
return False # so we can run every message through
if not ciphertext.startswith('I'):
@ -132,11 +131,13 @@ class common:
except BaseException as e:
return False
def wrap(self, text, target=None, b58=False, enc=False):
if target:
code = self.get_otp(target)
def wrap(self, text, handshake=False, target=None, b58=False, enc=False):
if handshake:
code = self.handshake_otp.get_otp_cast()
elif target:
code = self.otp.get_otp(target)
else:
code = self.get_otp_cast()
code = self.otp.get_otp_cast()
text = code + text
@ -150,13 +151,18 @@ class common:
def parse(self, text):
return self.dec(text) or self.from_b58(text) or text
def check_auth(self, text):
def check_auth(self, text, handshake=False):
try:
int(text[:6])
except ValueError:
return False
if self.check_otp(text[:6]):
if handshake:
check = self.handshake_otp
else:
check = self.otp
if check.check_otp(text[:6], me=self.TELEGRAM_ID):
return True
else:
return False
@ -168,18 +174,19 @@ class common:
def init(self):
self.init_secret = ''.join(random.choice(string.ascii_uppercase + string.digits) for _ in range(14))
self.otp = OTP(self.init_secret)
return self.get_pub()
def handshake(self, text):
self.init_secret = '' # clear it
self.master_pub = X25519PublicKey.from_public_bytes(base58.b58decode(text))
slave_pub = self.get_pub()
self.set_otp(slave_pub)
self.handshake_otp = OTP(slave_pub)
return slave_pub
def secret(self, text):
if not self.init_secret: return
self.set_otp(text)
self.handshake_otp = OTP(text)
slave_pub = X25519PublicKey.from_public_bytes(base58.b58decode(text))
shared_key = self.key.exchange(slave_pub)
derived_key = HKDF(SHA256(), length=32, salt=b'Qot.', info=None, backend=default_backend()).derive(shared_key)
@ -188,5 +195,6 @@ class common:
def set_secret(self, text):
shared_key = self.key.exchange(self.master_pub)
derived_key = HKDF(SHA256(), length=32, salt=b'Qot.', info=None, backend=default_backend()).derive(shared_key)
otp_secret = self.dec(text, derived_key)
return self.set_otp(otp_secret)
secret = self.dec(text, derived_key)
self.otp = OTP(secret)
return True

2
setup.py
View File

@ -5,7 +5,7 @@ with io.open('README.md', encoding='utf-8') as fh:
long_description = fh.read()
setuptools.setup(name='bwb',
version='2.0.3',
version='2.1.0',
description='bwb',
long_description=long_description,
long_description_content_type='text/markdown',