Re: Ostiary

2005-08-03 Thread Alexander Klimov
On Tue, 2 Aug 2005, Udhay Shankar N wrote:

 Sounds interesting. Has anybody used this, and are there any comments?

For similar purpose I used to use .qmail based system: the script
started from .qmail when a message to some special address arrives,
the script checks the digital signature on the message, compare the
first line with stored counter (to avoid replay attacks) and executes
the needed command. The positive side of this technique is that it is
very simple (just few lines to code), does not need to open a port
(and so it is firewall-friendly, no need to talk with sysadmins, ...),
very unlikely to introduce security holes (qmail has quite good
records, and in my case the mail was needed anyway).

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Ostiary

2005-08-02 Thread Udhay Shankar N

Sounds interesting. Has anybody used this, and are there any comments?

Udhay

http://ingles.homeunix.org/software/ost/


Tools like ssh and lsh are great for allowing secure remote access to your 
system. They offer essentially full, flexible remote control of a machine, 
in an ecrypted and authenticated manner. But they are complex pieces of 
software; there's no way to do what they do without being complex. And with 
complexity comes bugs. Tools like ssh and lsh, and VPNs like CIPE, PPTP, 
and more have all had serious flaws that would allow an attacker to get 
full control over your system.


If you leave such programs running all the time, you take the risk that 
someone is going to use an exploit on you before you have a chance to apply 
a patch. For some purposes, this is an acceptable - even necessary - 
tradeoff, but it would be nice to enable them only when actually needed, to 
minimize the risk. And for other purposes, ssh et. al. are overkill. 
Perhaps you only really need to remotely initiate a limited set of 
operations. In this case, you don't need a shell prompt, just a way to 
securely kick off scripts from elsewhere.


Enter 'Ostiary'. It is designed to allow you to run a fixed set of commands 
remotely, without giving everyone else access to the same commands. It is 
designed to do exactly and only what is necessary for this, and no more. 
The only argument given to the command is the IP address of the client, and 
only if the authentication is successful. The following are the key design 
goals:


   * First, do no harm. It should not be possible to use the Ostiary 
system itself to damage the host it's running on. In particular, it's 
willing to accept false negatives (denying access to legitimate users) in 
order to prevent false positives (allowing access to invalid users).
   * Insofar as possible, eliminate any possibility of bugs causing 
undesired operations. Buffer overflows, timing attacks, etc. should be 
impossible for an external attacker to execute. There's no point in 
installing security software if it makes you less secure.
   * Be extremely modest in memory and CPU requirements. I want to be able 
to fire off commands on my webserver (running on a Mac SE/30, a 16MHz 68030 
machine) from my Palm Pilot (a 16MHz 68000 machine). Things like ssh 
already take 30 seconds or more to start up - I can't afford anything too 
fancy.
   * Keep things simple. I'm no crypto expert; I know I'm not capable of 
coming up with an ssh replacement. So I need to keep things so utterly 
simple that I can be sure I'm not missing anything important.





--
((Udhay Shankar N)) ((udhay @ pobox.com)) ((www.digeratus.com))


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Re: Ostiary

2005-08-02 Thread Ian Grigg
On Tuesday 02 August 2005 13:26, Udhay Shankar N wrote:
 Sounds interesting. Has anybody used this, and are there any comments?
 
 Udhay
 
 http://ingles.homeunix.org/software/ost/

 ... 
 Perhaps you only really need to remotely initiate a limited set of 
 operations. In this case, you don't need a shell prompt, just a way to 
 securely kick off scripts from elsewhere.
 
 Enter 'Ostiary'. It is designed to allow you to run a fixed set of commands 
 remotely, without giving everyone else access to the same commands. It is 
 designed to do exactly and only what is necessary for this, and no more. 

I recently wrote this as a login program that was
hard coded to run the commands concerned.

The reason for doing this instead of the Ostiary
approach is that SSH had to be running anyway,
and SSH provides the key management regime.
Without that, I'd have to invent my own which
in Ostiary's case was the Hashing mechanisms.
So on this point it would come down to whether
we cared enough to replace SSH's authentication
regime, which I'd think would be rarer (perhaps
in the embedded market where Unix doesn't need
maintaining??).

Also, efficiency of command sending was not
an issue - each send was about 10 seconds in
my tests.


 * Keep things simple. I'm no crypto expert; I know I'm not capable of 
 coming up with an ssh replacement. So I need to keep things so utterly 
 simple that I can be sure I'm not missing anything important.

I think it is smart to keep things simple regardless
of ones expertise :)  Also, I wouldn't overdo the
hackability argument.  If flaws are found, you'll
find time to fix them, and for the cost of a few
hacked boxes, you'll have the benefit of a lot
more secured boxes.

iang
-- 
Advances in Financial Cryptography, Issue 2:
   https://www.financialcryptography.com/mt/archives/000498.html
Mark Stiegler, An Introduction to Petname Systems
Nick Szabo, Scarce Objects
Ian Grigg, Triple Entry Accounting

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Re: Ostiary

2005-08-02 Thread Karl Chen
As an authentication protocol, it looks vulnerable to a time
synchronization attack: an attacker that can desynchronize the server
and client's clocks predictably can block the client's authentication
and use it as his own.  (Assuming the server's clock is monotonically
increasing, the command can only be used once.)  If the command utilizes
the IP address (e.g. as a port knock), this is a security hole.

Karl

On Tue, 2005-08-02 at 17:56 +0530, Udhay Shankar N wrote:
 Sounds interesting. Has anybody used this, and are there any comments?
 
 Udhay
 
 http://ingles.homeunix.org/software/ost/


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Re: Ostiary

2005-08-02 Thread Nicolas Rachinsky
* Karl Chen [EMAIL PROTECTED] [2005-08-02 09:24 -0700]:
 As an authentication protocol, it looks vulnerable to a time
 synchronization attack: an attacker that can desynchronize the server
 and client's clocks predictably can block the client's authentication
 and use it as his own.  (Assuming the server's clock is monotonically

I don't see where the client's time is used. What am I missing?

Nicolas

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