Subject: [dns-privacy] DNS PRIVate Exchange

From: Tariq Saraj <[email-masked]>
Date: Wed, 13 Jan 2016 16:58:03 +0500

Hi all,
        I am working on my MS(InfoSec) Final Thesis "Lightweight solution
for confidentiality in DNS".
I just want to raise an issue about DNS confidentiality.
Encryption is only strong when we don't know about both decryption key and
plaintext.
In case with DNS, plaintext is always known. It just a matter of couple of
tries with domain names such as google, facebook, twitter, hotmail, yahoo
and youtube etc.
A simple xoring can return original key used for encryption.

-- 
Regards
Tariq Saraj
Center for Research in Networks and Telecom (*CoReNeT*)

---

From: Shane Kerr <[email-masked]>
Date: Wed, 13 Jan 2016 13:12:14 +0100

Tariq,

At 2016-01-13 16:58:03 +0500

> Encryption is only strong when we don't know about both decryption key and

I am by no means a cryptographer, but I am pretty certain that this is
not true.

https://en.wikipedia.org/wiki/Known-plaintext_attack

   "Modern ciphers such as Advanced Encryption Standard are not
   currently known to be susceptible to known-plaintext attacks."

> A simple xoring can return original key used for encryption.

Cheers,

--
Shane

---

From: Stephane Bortzmeyer <[email-masked]>
Date: Thu, 14 Jan 2016 09:16:22 +0100

On Wed, Jan 13, 2016 at 04:58:03PM +0500,
 Tariq Saraj <[email-masked]> wrote 
 a message of 62 lines which said:

> In case with DNS, plaintext is always known.

No, it is not (otherwise, encryption would be pointless).

> A simple xoring can return original key used for encryption.

:-D

---

From: Tariq Saraj <[email-masked]>
Date: Fri, 15 Jan 2016 11:31:09 +0500

Hi Stephane,
                  Unfortunately plaintext is known, I am going to work on
it once I complete the confidentiality implementation and soon InShaa'ALLAH
will share with the community.
I know there are a number of rounds and SBoxes involved, but currently
nothing have in hands to defend my concern strongly.
Finally, encryption can't prevent the attack completely but simply make it
difficult for the attacker.
Hope will enjoy discussing with you guru's on this issue in future.

---

From: Stephane Bortzmeyer <[email-masked]>
Date: Fri, 15 Jan 2016 10:15:15 +0100

On Fri, Jan 15, 2016 at 11:31:09AM +0500,
 Tariq Saraj <[email-masked]> wrote 
 a message of 80 lines which said:

> Unfortunately plaintext is known,

As I said, it is not. You can sometimes *guess* some of the questions
and answers (it is safe to assume that the user's machine will query
google-analytics.com at least from time to time), it does not give you
the full plaintext (query ID, for instance). And, as Shane explained
(you should have read it), modern crypto is not vulnerable to
"known-plaintext attacks".

> I am going to work on it once I complete the confidentiality
> implementation

May I suggest that you learn some crypto first, as well as reading RFC
7626 and the other DPRIVE documents? Check also the implementations
(there are several of DNS-over-TLS, as well as the nonstandard
DNScrypt).

---

From: Robert Edmonds <[email-masked]>
Date: Fri, 15 Jan 2016 11:47:48 -0500

> "known-plaintext attacks".

Not just modern crypto, apparently (if you believe Wikipedia), there was
at least one electro-mechanical encryption machine that was "considered
secure against known plaintext attack", at least by its vendor:

    https://en.wikipedia.org/wiki/KL-7

    In 1952, the machine was introduced by AFSA's successor, the U.S.
    National Security Agency, in the US Army, Navy and Air Force. In the
    early 1960s, the AFSAM-7 was renamed TSEC/KL-7, following the new
    standard crypto nomenclature. It was the most widely used crypto
    machine in the US armed forces until the mid-1960s and was the first
    machine capable of supporting large networks that was considered
    secure against known plaintext attack. The KL-7 was also used by
    several NATO countries until 1983.

-- 
Robert Edmonds