On 4/9/2018 11:00 AM, Warren Kumari wrote:

> On Mon, Apr 9, 2018 at 1:53 PM Christian Huitema <huit...@huitema.net
> <mailto:huit...@huitema.net>> wrote:
>
>     At first sight, it seems that this moves the logging hole from the
>     DNS recursive to the ODNS recursive, and that's a meh.
>
>     Also, instead of using a complicated tunneling through the
>     recursive resolver via name obfuscation, why not establish a
>     secure connection to the ODNS server in the first place?
>
>
> The ODNS server doesn't know the client IP (it gets occluded by the
> rescursive server), and the rescursive doesn't know the question. This
> is kinda somewhat similar to the Tor model.
>
> This is a fairly common question - I think that the ODNS documents /
> people should clarify this better..

They should really clarify the problem that they are addressing. As
Shumon said, if the goal is to hide the source IP address from the
recursive resolver, then it seems that "DNS over onion routing" would be
easier to engineer and deploy than "oblivious DNS".

They should also clarify the use of symmetric key encryption. Is the
symmetric key specific to a client-server pair, or is shared by the
server with a large group of clients? If the key is specific to a
client, then it identifies the client even if the IP address is hidden.
If the key is widely shared instead, then it takes only one bad client
for the key to leak, and the traffic logs at the recursive DNS can be
de-obfuscated.

From an engineering point of view, I am concerned with applications of
encryption to small size objects like name part or IP addresses. Modern
symmetric algorithms operate on 128 bit blocks, with mainline AEAD
encryption adding 16 bytes of overhead to the object. That's bad enough,
but asymmetric algorithms are even worse. Even if you use Elliptic Curve
crypto, the smallest practical key is 256 bits, or 32 octets. The
overhead will make that impractical. If we happen to need longer keys it
will just not fit in the 63 octets of a domain name part, even if we
found a way to not require Base64 encoding. I am much more confident
that we can solve the engineering issues if we develop an encrypted
transport with onion routing.

-- Christian Huitema


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