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Re: Does your software?

On Tue, 24 Oct 1995, Jon Mittelhauser wrote:

> Dr. Frederick B. Cohen wrote:
> > Yet it services more than one request per minute, 24 hours, 7 days, and
> > has done so without denial of services, corruption, or leakage since its

> I really tried to resist but....

Thanks for saving me from the temptation but I guessed you were so taken 
aback by the performance claims that you missed the most amazing claim: 
an httpd that is proof against Denial Of Service. I'd love to know how 
Dr. Fred does this, since DoS is believed impossibly to defend against 
for unauthenticated TCP...

The usual DoS attack is to send a stream of connection-initiating SYNs to 
the target port, and never ACK the returned SYN. This fills up the listen 
queue, and jams the port. As long as you can generate SYNs faster than 
the TCP implementation times out the older pending requests, the port is 
jammed (modulo a small window of, er, invunerability between one of your 
SYNs timing out and its replacement turning up). 

Ob Crypto:

  Has anybody thought about running Photuris over a TCP connection to do 
application-level key-exchange? The cookie stuff isn't really needed in 
this application, but it's still quite a nice wheel.


(defun modexpt (x y n)  "computes (x^y) mod n"
  (cond ((= y 0) 1) 	((= y 1) (mod x n))
	((evenp y) (mod (expt (modexpt x (/ y 2) n) 2) n))
	(t (mod (* x (modexpt x (1- y) n)) n))))