Bump 2FA secret bit length from 80 bits to 160 bits as recommended by…

… RFC4226

securedrop/models.py

@@ -4,6 +4,8 @@
 import base64
 import os
 import scrypt
+import secrets
+import string
 import pyotp
 import qrcode
 # Using svg because it doesn't require additional dependencies
@@ -35,6 +37,17 @@
 ARGON2_PARAMS = dict(memory_cost=2**16, rounds=4, parallelism=2)
 
 
+def generate_otp_secret() -> str:
+    """
+    Generate an OTP secret of 160 bits
+
+    For usability reasons the return charset is variation
+    of base32 that does not include any symbol in [O,0,I,1]
+    """
+    symbols = list('ABCDEFGHJKLMNPQRSTUVWXYZ23456789')
+    return ''.join(secrets.choice(symbols) for i in range(32))
+
+
 def get_one_or_else(query: Query,
                     logger: 'Logger',
                     failure_method: 'Callable[[int], None]') -> db.Model:
@@ -403,7 +416,7 @@ class Journalist(db.Model):
     is_admin = Column(Boolean)  # type: Column[Optional[bool]]
     session_nonce = Column(Integer, nullable=False, default=0)
 
-    otp_secret = Column(String(16), default=pyotp.random_base32)
+    otp_secret = Column(String(32), default=generate_otp_secret)
     is_totp = Column(Boolean, default=True)  # type: Column[Optional[bool]]
     hotp_counter = Column(Integer, default=0)  # type: Column[Optional[int]]
     last_token = Column(String(6))
@@ -566,7 +579,7 @@ def valid_password(self, passphrase: 'Optional[str]') -> bool:
         return is_valid
 
     def regenerate_totp_shared_secret(self) -> None:
-        self.otp_secret = pyotp.random_base32()
+        self.otp_secret = generate_otp_secret()
 
     def set_hotp_secret(self, otp_secret: str) -> None:
         self.otp_secret = base64.b32encode(