Re: [PROPOSAL/PATCH] Fortuna PRNG in /dev/random

[Jean-Luc Cooke]

On Mon, Sep 27, 2004 at 08:07:19PM -0400, Theodore Ts'o wrote:
> On Mon, Sep 27, 2004 at 03:45:02PM -0400, Jean-Luc Cooke wrote:
> > > Actually trying to replace the partial MD4 might be worth an attempt: 
> > > I'm certain that the partial MD4 is not the best/fastest way to generate 
> > > sequence numbers.
> > 
> > It infact uses two full SHA1 hashs for tcp sequence numbers (endian and
> > padding issues aside).  my patch aims to do this in 1 AES256 Encrypt or 2
> > AES256 encrypts for ipv6.
> 
> No, that's not correct.  We rekey once at most every five minutes, and
> that requires a SHA hash, but in the normal case, it's only a partial MD4.

Pardon, the SYN cookies use two SHA1's, not the TCP sequence numbers.  Easy
to mistake to make with comments "Compute the secure sequence number." in the
secure_tcp_syn_cookie() function.  :)

> An AES encrypt for every TCP connection *might* be faster, but I'd
> want to time it to make sure, and doing a bulk test ala "openssl
> speed" isn't necessarily going to be predictive, as I've discussed earlier.

Agreed.

Was meaning to ask:
  add_timer_randomness()

There is a comment:
  /* if over the trickle threshold, use only 1 in 4096 samples */
  if ( random_state->entropy_count > trickle_thresh &&
	(__get_cpu_var(trickle_count)++ & 0xfff))
		return;

"if (x++ & 0xfff)" will return true 0xfff out of 0x1000 of the time.  Is this
the goal, because I don't think this will trickle control very well.

JLC
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