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Avoid leaking user existence info #180

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Avoid leaking user existence info #180

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29 changes: 25 additions & 4 deletions etebase_server/fastapi/routers/authentication.py
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Original file line number Diff line number Diff line change
@@ -1,3 +1,4 @@
import random
import typing as t
from typing_extensions import Literal
from datetime import datetime
Expand Down Expand Up @@ -122,16 +123,36 @@ def get_login_user(request: Request, challenge: LoginChallengeIn) -> UserType:
raise AuthenticationFailed(code="user_not_init", detail="User not properly init")
return user
except User.DoesNotExist:
raise AuthenticationFailed(code="user_not_found", detail="User not found")
return fake_user(username)


def get_encryption_key(salt: bytes):
FAKE_USER_COUNT = 1000


def fake_user(username: str) -> UserType:
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It's a good idea, but this is unfortunately not effective.

The returned user id is random every time, so just hit this API twice to check for existence. Additionally, I haven't had the time to analyze the using of static pubkeys/salts but I'm concerned that may have issues too.

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The returned user id is random every time, so just hit this API twice to check for existence.

Oh, you are absolutely right, didn't think of that

username_bytes = bytes(username, encoding="utf-8")
login_pubkey = get_encryption_key(b"", b"loginPubkey", username_bytes)[:32]
salt = get_encryption_key(b"", b"salt", username_bytes)[:16]

user = User()
user.username = username
user.id = random.Random(settings.SECRET_KEY + username).randint(0, FAKE_USER_COUNT)

userinfo = UserInfo()
userinfo.loginPubkey = login_pubkey
userinfo.salt = salt

user.userinfo = userinfo
return user


def get_encryption_key(salt: bytes, person=b"etebase-auth", data: bytes = b""):
key = nacl.hash.blake2b(settings.SECRET_KEY.encode(), encoder=nacl.encoding.RawEncoder)
return nacl.hash.blake2b(
b"",
data=data,
key=key,
salt=salt[: nacl.hash.BLAKE2B_SALTBYTES],
person=b"etebase-auth",
person=person,
encoder=nacl.encoding.RawEncoder,
)

Expand Down