RE: Concepts: Security and Obscurity

["Craig Wright" <Craig.Wright () bdo com au>]

Hi Daniel,
I admit that I missed some of the posts initially concerning port
knocking etc and thus I did not consider this in my initial response.

Port knocking has the issue that it is not completely silent as is
presumed. Most routers are not set to stop sending ICMP, TCP etc
responses to other routers. In fact to do so is a violation of the
internet standards. As such, information on ports is often available
from the network infrastructure. Drop on firewalls does not stop an
attacker finding what ports are running - it just means that they have
to be a little more creative.

Systems that ONLY drop packets stand out. They are not "stealthy" but
rather the hole they make makes them extrememly visible.

In port knocking the control is not highly effective, to take a quote:

In 'Critique of Port Knocking', Arvind Narayana states:
"Suppose you decide on a list of 32 valid ports (the current
implementation
allows up to 256). How long does the port knock sequence
need to be? You might think that since each port is a 16-bit integer,
you need 8 knocks, so that you get 8*16 bits or 128 bits of security
(virtually unbreakable). But since each port has only 32 possible
values (5 bits), what you actually get is only 8*5=40 bits of security
(trivially breakable)!"

Applied Cryptography by Bruce Schneier:
"If I take a letter, lock it in a safe, hide the safe somewhere in New
York, then tell you to read the letter, that's not security. Thats
obscurity. On the other hand, if I take a letter and lock it in a
safe, and then give you the safe along with the design specifications
of the safe and a hundred identical safes with their combinations
so that you and the worlds best safecrackers can study the locking
mechanism - and you still can't open the safe and read the letter -
thats security."

Regards,
Craig

Narayanan A. (2004) 'A Critique of Port Knocking'. Newsforge, August
2004.
Viewable from:
http://software.newsforge.com/software/04/08/02/1954253.shtml



Craig Wright
Manager of Information Systems

Direct +61 2 9286 5497
Craig.Wright () bdo com au

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-----Original Message-----

From: Daniel Miessler [mailto:daniel () dmiessler com] 
Sent: Thursday, 12 April 2007 11:08 AM
To: Craig Wright
Cc: krymson () gmail com; security-basics () securityfocus com
Subject: Re: Concepts: Security and Obscurity


On Apr 11, 2007, at 5:55 PM, Craig Wright wrote:

> Except that the **Very* few is NOT 50,100 or even 1000 - it is many  
> many
> times that. Unless you have cheanged the nature of the hypothesis as I
> suspect that you have done in the response (ie limiting access
> addresses)

Changed the nature of the hypothesis? What thread have you been  
reading? Have you even RTA? I'm going to stop this here since you  
don't seem to understand what PK or SPA is.

Go back, check it out, and then we'll start again if there's any  
confusion. I have a feeling you're a pretty bright guy who's simply  
not talking about the same thing we are.

--
Daniel Miessler
E: daniel () dmiessler com
W: http://dmiessler.com
G: 0xDA6D50EAC